2016, 日本燃焼学会, 平成28年度日本燃焼学会 奨励賞　　　　　　　　　　　　　　　
寺島洋史

Numerical Study of Cryogenic Hydrogen Jet in Crossflow under Supercritical Pressure: Comparison of Tandem and Twin Jets
NAKATSUKASA Tomohito, AMANO Taishi, ARAKI Takahide, TERASHIMA Hiroshi, TSUBOI Nobuyuki, OZAWA Kohei
Journal of Evolving Space Activities, 1, n/a, International Symposium on Space Technology and Science, 2023, [Peer-reviewed]
English, The present study numerically investigates the flow fields of the twin- and tandem-jet in crossflow (JIC) under supercritical pressure. An ILES/RANS method is applied. In the present JIC, cryogenic hydrogen jets are vertically injected to warm temperature hydrogen crossflow through circular injector holes. The results show that the penetration of cryogenic jets into the crossflow is more enhanced with the tandem-jet than with the twin-jet. The higher jet penetration with the tandem jets is caused by a downstream jet behavior less influenced by the crossflow. Nevertheless, a mixedness analysis indicates that the mixing state at a downstream position is almost similar between the tandem and twin jets.

Numerical Investigation of Transonic Flutter Characteristics of a Supercritical Airfoil
Toma Miyake, Hiroshi Terashima
Lecture Notes in Electrical Engineering, 912, 607, 621, 2023
International conference proceedings, This study numerically investigates the transonic flutter characteristics of a supercritical airfoil and discusses the similarities and differences compared to a conventional symmetric airfoil. A wing-section model with two-degree-of-freedom was adapted. An SC2-0610 supercritical airfoil was used for the investigation, and the results were compared with those of the NACA64A010 airfoil. Overall, similar flutter characteristics, such as transonic dip appearance, were observed between the two airfoils. The effect of the shape of the supercritical airfoil appears as the angle of attack effect; for example, the supercritical airfoil with an angle of attack of −2°(0°) shows qualitatively similar flutter characteristics to the NACA64A010 airfoil with an angle of attack of 0°(2°). Furthermore, in the present study, the supercritical airfoil exhibits unique flutter characteristics under high Mach number conditions because of the development of flow separation near the trailing edge on the lower surface. In particular, when the Mach number was 0.875, the flow reattachment near the trailing edge on the lower surface generated a high-pressure region, which induced a unique flutter oscillation under the second torsion mode.

A Computational Study on Unsteady Aerodynamic Forces Around a Pitching Airfoil with Shock and Shock-Induced Separation
Noah D. Oyeniran, Hiroshi Terashima
Lecture Notes in Electrical Engineering, 912, 353, 360, 2023
International conference proceedings, The present study computationally investigates the characteristics of unsteady aerodynamic forces around an oscillating airfoil in the transonic flow regime. Particular attention is paid to the role of shock wave and shock-induced boundary layer separation in unsteady aerodynamics. The Reynolds-averaged compressible Navier–Stokes equations are solved with SA and SST turbulence models. A well-known forced-pitching NACA64A010 airfoil experiment (Sanford and Gerald in AIAA J 11:1306–1312, 1980, [6]) is simulated, and the freestream Mach number, Reynolds number, and reduced frequency are set to 0.8, 1.2 × 107, and 0.2, respectively. The pitching airfoil with mean angles of attack of 0°, 2°, 4°, and 6° having the amplitude of 1° is parametrically simulated. It is observed that at the mean angle of attack of 0°, there is a phase delay of the lift coefficient against the angle of attack due to the delay of a shock wave movement over the airfoil surface. In contrast, a phase-advanced feature of unsteady aerodynamics appears in increasing the mean angle of attack (e.g., 4° and 6°). There is a phase transition of unsteady aerodynamics from the delay to advance, significantly caused by the appearance of shock-induced boundary-layer separation. The mean angle of attack around 3° may correspond to a transition condition between the phase-delayed and phase-advanced features. The present study demonstrated that the trend of the unsteady aerodynamic characteristics around the transonic oscillating airfoils largely changes with the mean angle of attack. The shock wave, the shock-induced separation, and their interaction play a crucial role in determining the unsteady aerodynamics such as the phase-delayed or the phase-advanced features.

Unsteady Aerodynamics Around a Pitching Airfoil with Shock and Shock-Induced Boundary-Layer Separation
Noah D. Oyeniran, Toma Miyake, Hiroshi Terashima, Ryoto Seki, Keiichi Ishiko, Taku Nonomura
AIAA Journal, 07 Oct. 2022, [Peer-reviewed], [Corresponding author]
Scientific journal

Mechanisms for severe combustion instabilities induced by low-temperature fuel injection of an H2/O2 rocket-type combustor
Toru Ota, Hiroshi Terashima, Nobuyuki Oshima
AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2022, 2022
International conference proceedings, Combustion instabilities are a significant issue in combustion engine developments and operations. The present study numerically investigates combustion instabilities that happen in a high-pressure H2/O2 rocket-type combustor. The effects of fuel temperature on combustion instability are discussed. The compressible Navier-Stokes equations are solved with a detailed chemical mechanism, and a two-dimensional planar combustor model with a single injector is used for investigation. The simulation result demonstrates that the fuel injection temperature significantly affects the combustion instability feature, such as acoustic wave development. While the fuel injection with a room temperature results in stable combustion, the low-temperature fuel injection causes severe pressure oscillations with large amplitudes. The frequency analysis confirms that the pressure oscillation occurs in the first longitudinal mode of the combustor, i.e., the thermoacoustic combustion instability happens. The pressure (acoustic) wave development is caused by the heat release of unburned gas that remained in the near-field of the injector. For lower-temperature injection cases, a relatively large amount of unburned gas exists due to the delay of combustion, and thus the potential of pressure wave development in coupling with the heat release becomes higher. The development process may correspond to the deflagration-to-detonation process.

Prediction of propagating flames under high-pressure conditions with real-fluid combustion modeling
Hiroshi Terashima, Mitsuo Koshi
Proceedings of the Combustion Institute, 2022, [Peer-reviewed], [Lead author, Corresponding author]
Scientific journal, The present study discusses computational fluid dynamics (CFD) modeling for combustion flows under high-pressure conditions, including supercritical pressure conditions. The real-fluid effects are considered in terms of thermodynamic properties, transport properties, and chemical kinetics. In the present model, the real-fluid effect on chemical kinetics is introduced via a modified equilibrium constant derived using the Gibbs free energy variation of chemical reactions and the fugacity. The results obtained with the present model are compared with available experimental data of high-pressure premixed H2/O2 propagating flames diluted by Ar or He. We demonstrate in the H2/O2/Ar flame case that the real-fluid model provides a better prediction accuracy for the negative pressure dependence of the mass burning rate compared to the ideal-gas model. The improved prediction accuracy is primarily attributed to the proper estimation of thermodynamic properties such as unburnt-gas enthalpy via an appropriate equation of state and a departure function. The negative pressure dependence of unburnt-gas enthalpy of the H2/O2/Ar mixture with the real-fluid model significantly affects the flame speed prediction under high-pressure conditions. On the other hand, although the H2/O2/He mixture shows a positive pressure dependence of enthalpy, differences in the mass burning rate between the real-fluid and ideal-gas models are not significant for the H2/O2/He flame case. In the He-diluted case, the real- fluid effect is undermined owing to the low density of the H2/O2/He mixture. Thus, the real-fluid effect appears differently in the prediction of propagating flames depending on the species composition and thermodynamic conditions. The present study suggests that the positive or negative pressure dependence of enthalpy (i.e., the isothermal Joule-Thomson coefficient) is a metric to identify the real-fluid effects that appear.

Effects of a Recess on Coaxial Cryogenic Injections at Supercritical Pressure
Daiki Muto, Hiroshi Terashima, Takahide Araki, Nobuyuki Tsuboi
Journal of Propulsion and Power, 38, 4, 581, 591, 2022, [Peer-reviewed]
Scientific journal, Effects of recess lengths on coaxial cryogenic jets under a supercritical pressure are numerically studied. A hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes methodology is applied to capture unsteady jet behaviors of recessed injectors. For the injector with a moderate recess length, the dense-core length of the inner jet is shorter than that with a nonrecessed injector, demonstrating that recessing improves the mixing. The flowfields show that the vortex structures in an inner mixing layer are strongly developed within the recessed region, and the entrainment of the outer jet into the inner jet is strengthened. However, a further increase in the recess length turns to the increase of the dense-core length and deteriorates the inner jet decay along the centerline. This deterioration is caused by the separation of the outer jet flow on the wall in the recessed region. The turbulence generation in the outer mixing layer is suppressed because of the separation, resulting in less enhancement of the mixing in the downstream region. Therefore, the study demonstrates that there is an approximate recess length for optimum jet mixing. Finally, a correlation relationship is provided between the dense-core length and the momentum flux ratio from a comprehensive comparison of existing experimental and numerical data.

Effects of Globally Stratified Temperature Distributions and NTC Characteristics on End-gas Combustion Modes
Takahisa Nogawa, Hiroshi Terashima
Combustion Science and Technology, 194, 7, 1433, 1457, 2022, [Peer-reviewed], [Corresponding author]
Scientific journal, This study numerically investigates the effects of stratified temperature distributions on the end-gas combustion mode in a constant volume reactor. The initial temperature in the reactor was globally stratified with linear gradients. The effects of negative temperature coefficient (NTC) characteristics are addressed through a comparison between the results of a non-NTC fuel and an NTC fuel. The compressible Navier–Stokes equations are solved with detailed chemistry. The results show that the addition of large temperature gradients such as −10 or −5 K/cm can prevent the pressure wave development associated with end-gas autoignition, and the knocking intensity is significantly reduced. In contrast, small temperature gradients such as −1 K/cm lead to the generation of the developing detonation mode and thus to large knocking intensities. In the NTC fuel case, the knocking intensity becomes relatively large because the spatial gradient of the ignition delay time decreases even with the addition of large temperature gradients, especially in the NTC regime. Based on all the results, a correlation is presented between the initial temperature and the reaction front speed (the spatial gradient of the ignition delay time) for the prediction of end-gas combustion mode. The correlation suggests that the possibility of preventing large knocking intensities by temperature gradients is reduced under high-pressure conditions because of the increase in the reaction front speed. Consequently, this study suggests that very large temperature gradients would be required under high-pressure conditions to prevent large knocking intensities under the concept of thermal stratification.

Fuel Effects on the Combustion Flow Structure behind a Splitter Plate of a Rocket Injector
Shun MURAKAMI, Hiroshi TERASHIMA, Nobuyuki OSHIMA
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 19, 2, 176, 185, Japan Society for Aeronautical and Space Sciences, 2021, [Peer-reviewed]
Scientific journal

A localized thickened flame model for simulations of flame propagation and autoignition under elevated pressure conditions
Hiroshi Terashima, Yutaka Hanada, Soshi Kawai
Proceedings of the Combustion Institute, 38, 2, 2119, 2126, Jan. 2021, [Peer-reviewed], [Lead author, Corresponding author]
Scientific journal, The present study proposes a localized thickened flame (LTF) model for the accurate prediction of flame propagation and autoignition timing. The unresolved-scale terms appeared in spatially-filtered governing equations due to thin flame structures are constructed under a physical constraint in which laminar flame speed is maintained. A high-order derivative is introduced to dynamically localize the effects of the LTF in the regions of unresolved propagating flame. The model is also designed such that the thickened flame is resolved by the same number of grid points for any grid size used. Therefore, a user-specified constant in the model does not need to be adjusted depending on the employed grid size. Laminar flame propagation problems are used to validate the performance of the proposed LTF model and determine the appropriate value of the user-specified constant. The results using a one-dimensional constant-volume reactor demonstrate that the LTF successfully captures the accurate flame propagation behaviors under elevated pressure conditions, while not affecting the end-gas autoignition timing, even on relatively coarse grid resolutions. The high-order derivative in the LTF serves as a dynamic parameter for detecting the thinning flame under elevated pressure conditions.

Role of low-temperature oxidation in non-uniform end-gas autoignition and strong pressure wave generation
Hiroshi Terashima, Hisashi Nakamura, Akira Matsugi, Mitsuo Koshi
Combustion and Flame, 223, 181, 191, Jan. 2021, [Peer-reviewed], [Lead author, Corresponding author]
Scientific journal, This study highlights the importance of heat release rate in low-temperature oxidation (LTO) on non-uniform end-gas autoignition and strong pressure wave generation, which are substantially relevant to knocking combustion. The simulations are conducted using the compressible Navier–Stokes equations with detailed transport and chemical kinetics models in a one-dimensional constant-volume reactor. Four fuel/air stoichiometric mixtures, n-butane, i-octane, n-heptane, and dimethyl ether (DME)/air mixtures, are simulated. The results show that larger knocking intensities are produced with n-heptane and DME in their negative temperature coefficient (NTC) regimes because of the stronger non-uniformity of end-gas autoignition. The non-uniformity of end-gas autoignition is enhanced by a pressure wave disturbance that is caused by the rapid temperature rise of the end-gas region in LTO. In particular, the high heat release rate with the DME/air mixture generates a distinct pressure wave disturbance in the reactor, which considerably enhances the non-uniformity of end-gas autoignition through the reflection of the wave at the wall. In contrast, the heat release rate in the n-heptane case is milder than that in the DME case, and therefore, the knocking intensity in the n-heptane case is smaller compared to that of DME due to less enhancement of the non-uniform end-gas autoignition. No large knocking intensities are produced with n-butane and i-octane, which have weak NTC, because of the absence of a temperature rise in LTO. Thus, this study concludes that the high heat release rate in LTO and the generated pressure wave disturbance play a significant role in the generation of large knocking intensities through the enhancement of non-uniform end-gas autoignition.

End-gas autoignition behaviors under pressure wave disturbance
Terashima, Hiroshi, Matsugi, Akira, Koshi, Mitsuo
COMBUSTION AND FLAME, 203, 204, 216, ELSEVIER SCIENCE INC, May 2019, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, The present study addresses effects of pressure wave disturbance on end-gas autoignition behavior and subsequent pressure wave development, which are of particular interest for understanding a fundamental process of knocking combustion in spark-assisted ignition engines. Such pressure wave disturbance is initiated by a compression wave generated from spark-like ignition and continuously exists in a combustion chamber. The investigation is conducted through a direct numerical simulation with a 1-D constant volume reactor, where the compressible Navier-Stokes equations are solved with detailed reaction mechanisms of n-C7H16 and n-C4H10/air mixtures. The width of an ignition kernel parametrically changes in order to control the strength of an initial compression wave and thus pressure wave disturbance. The result showed that stronger compression waves with larger kernel widths enhance the progress of the autoignition process at the wall through the transient increase in pressure and temperature due to the wave reflection. Consequently, stronger pressure waves such as a developing detonation are generated with the enhanced inhomogeneous end-gas autoignition starting from the wall. In contrast, weak pressure wave disturbance produces no strong pressure waves due to the lower inhomogeneity of autoignition timing in an end-gas region. An analysis with temperature variation in an end-gas region indicates that cool flame generation helps maintain the superiority of the wall for earlier autoignition through the heat release at an earlier stage. Therefore, a stronger pressure wave associated with inhomogeneous end-gas autoignition is likely generated around 650 K in the case of an n-C7H16/air mixture, which corresponds to a distinct peak generation of knocking intensity in the negative temperature coefficient regime. For lower temperature conditions such as 500 K, the end-gas autoignition first takes place in a region away from the wall. This is because the initially induced temperature inhomogeneity in the end-gas region is considerably weakened due to wave interactions and dissipation effects during longer ignition delay times. Thus, multiple end-gas points including the wall can become a preferred point for earlier end-gas autoignition, resulting in a variation of end-gas autoignition locations. The result for an n-C4H10 air mixture is finally shown and the difference from that for the n-C7H16/air mixture is highlighted. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A computational study for combustion flow fields of a high-pressure gaseous hydrogen/oxygen coflow jet behind a splitter plate
Shun Murakami, Hiroshi Terashima, Nobuyuki Oshima
AIAA Scitech 2019 Forum, 2019
International conference proceedings, A computational study is performed for exploring flow and flame dynamics of a high-pressure hydrogen/oxygen coflow jet with the effects of post thickness and moment flux ratio. A two-dimensional model with a splitter plate, which represents a post configuration of an injector of rocket engines, is adapted to fully resolve the combustion flow field. The compressible Navier-Stokes equations are solved with a detailed chemical kinetic mechanism in a manner of direct numerical simulation. The result shows that the post thickness largely affects the temperature distribution in a recirculation region established behind the post. The temperature distribution is determined with the amount of incoming high-temperature combustion gas and unburned hydrogen gas, which significantly changes with the post thickness. The effect of the momentum flux ratio clearly appears in the case of thicker post configuration, while in the case of thinner post configuration no major differences are identified for all the momentum flux ratio. The study shows a tendency that thicker post geometries with smaller J numbers provide lower temperature fields in the recirculation region behind the post, thus preliminarily indicating some difficulty of maintaining a flame anchoring in the recirculation region.

Simulation for flame holding/extinguishing mechanisms on a laminar non-premixed flame of ammonia/O2/N2
Mahiro Ooe, Hiroshi Terashima, Jun Hayashi, Fumiteru Akamatsu, Nobuyuki Oshima
12th Asia-Pacific Conference on Combustion, ASPACC 2019, 2019
International conference proceedings, Ammonia is regarded as one of alternative fuels because of no CO2 emission during the combustion process. In this study, we numerically investigate details of flame holding/extinguishing mechanisms for a laminar non-premixed burner flame. The compressible Navier-Stokes equations with a detailed chemical kinetics of ammonia are applied in a manner of direct numerical simulation. The present result shows that increasing the rim thickness of a burner helps extend flame-holding conditions through the formation of larger recirculation region established behind the burner rim. However, further increase of the rim thickness eventually provides an unfavorable effect because of the decrease of heat release rate and the increase of heat loss to the rim wall. Thus, there exists an optimum rim thickness for increasing flame-holding capability.

Effects of a recess on supercritical co-flowing planar jets
Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi
Transactions of the Japan Society for Aeronautical and Space Sciences, 62, 4, 203, 212, Jan. 2019, [Peer-reviewed]
English, Scientific journal, © 2019 The Japan Society for Aeronautical and Space Sciences. The effects of a recess on co-flowing planar jets under supercritical pressure are numerically studied. Two-dimensional hybrid LES/RANS simulations are performed in a wide range of recess lengths and injection momentum flux ratios, which are important design parameters for liquid rocket engine injectors. The present study showed that confinement effects of the near-injector flowfield by applying a recess, suppress outer jet spreading and thus enhances the penetration of the outer jet flow into the inner jet. The enhanced penetration of the outer jet flow results in the appearance of flapping motions in the inner jet. Low-frequency oscillations corresponding to the flapping motions clearly appear in the case of recessed injectors. Moreover, the confinement effects promote interactions between vortex structures resulting in vortex breakdown. Consequently, the inner-jet length is shortened, indicating an improvement in mixing when a recess is applied. The present results also show that the inner-jet length deceases as the recess length increases, and the effects of a recess remarkably appear at higher momentum flux ratios. This is explained by the vortices generated behind the post lip that is strengthened as the result of increased velocity ratio.

Computational simulation of shock-bubble interaction, using a front-tracking/ghost fluid method
A. Razmi, M. Taeibi-Rahni, H. R. Massah, H. Terashima, H. Moezzi
Journal of Applied Fluid Mechanics, 12, 2, 631, 645, Jan. 2019, [Peer-reviewed]
English, Scientific journal, © 2019 Isfahan University of Technology. A front tracking/ghost fluid method was used to simulate fluid interfaces in a shock-bubble interaction problem. The method captures fluid interfaces, using explicit front-tracking and defines interface conditions, using the ghost-fluid method. In order to demonstrate the accuracy and the capability tracking of the approach used, an air-helium and anair-R22 shock-bubble interaction cases were simulated. The computational results were compared with reliable experimental and computational studies, showing close agreements.

The effects of equivalence ratio on pressure wave development during knocking combustion
D Deb, MA Uddin, H Terashima, N Oshima
Journal of Scientific Research, 10, 2, 117, 131, 2018, [Peer-reviewed]
English, Scientific journal

A Numerical Study on Hypergolic Combustion of Hydrazine Sprays in Nitrogen Tetroxide Streams
Hiroumi Tani, Hiroshi Terashima, Yu Daimon, Mitsuo Koshi, Ryoichi Kurose
COMBUSTION SCIENCE AND TECHNOLOGY, 190, 3, 515, 533, TAYLOR & FRANCIS INC, 2018, [Peer-reviewed]
English, Scientific journal, Unsteady simulations of hydrazine (N2H4) sprays in nitrogen tetroxide (NTO, NO2-N2O4) streams were conducted to explore the hypergolic combustion in bipropellant thrusters. The Navier-Stokes equations were solved using a detailed chemical kinetics mechanism and dispersed droplets were modeled through direct numerical simulations. Auto-ignition occurred when the sum of the heat transfer from the ambient gas and the heat release from hydrogen abstraction reactions exceeded the latent heat of the droplets. Although the evaporation of the droplets was enhanced as the droplet size decreased, the ignition delay time increased due to the lower temperatures of the mixtures of the N2H4 vapor and nitrogen tetroxide. After the flames reached a steady state, a double flame structure appeared, comprised of outer diffusion and inner decomposition flames. The inner decomposition flame and N2H4 vapor flow exhibited a sinusoidal behavior at a certain droplet size. This behavior was initiated by the locally expanded decomposition gases and developed by the supply of N2H4 droplets to the decomposition gases at relatively high temperatures. In cases of larger and smaller droplet sizes, the sinusoidal behavior was not significant due to less evaporation of the N2H4 droplets and a lower temperature of the N2H4 vapor, respectively. The sinusoidal behavior of the decomposition flames enhanced the mixing and reactions of the fuel components (i.e., N2H4, NH3, and H-2). The present study demonstrated a large impact of droplet size on flame dynamics, suggesting that a fine spray is not always better for hypergolic propellant combustion to consume the fuel components quickly.

Aerodynamic instability of flare-type membrane inflatable vehicle in suborbital reentry demonstration
Ohashi Tatsushi, Takahashi Yusuke, Terashima Hiroshi, Oshima Nobuyuki
JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, 13, 3, 2018, [Peer-reviewed]
Scientific journal, An inflatable membrane reentry vehicle has been developed as one of the innovative reentry technologies. A suborbital reentry demonstration using a sounding rocket was carried out in 2012. Contrary to the result of a preliminary study, the vehicle always had an angle of attack (AoA) during its reentry. In addition, the amplitude of AoA gradually increased as altitude decreased, and the vehicle rotated vertically under Mach number of 0.1 (M0.1). As a first step to clarify the cause of attitude instability and vertical rotation, the aerodynamic characteristics, that concern static stability, are numerically investigated. Numerical simulations were carried out for the cases of Mach 0.9 (M0.9), 0.6 (M0.6), 0.3 (M0.3), and 0.1 (M0.1) and pitching moment coefficients (CM) were obtained. Analysis software "RG-FaSTAR" for M0.9, and "FrontFlow/red" for M0.6, M0.3 and M0.1, are used, respectively. Large eddy simulation (LES) was performed using the standard Smagorinsky model to resolve highly unsteady flow features. Because the slope of CM with respect to AoA was negative for all cases, it was found that the vehicle is statically stable. For M0.9, M0.6 and M0.3 cases, absolute values of CM were almost the same. On the other hand, for M0.1, CM had a particularly large value, because the surface pressure distribution on rear side of the vehicle was different from the other cases. This difference was attributed to the separation point on the lower torus moving backward and turbulence in wake being enhanced with a decrease in Mach number and an increase in the Reynolds number.

Origin and reactivity of hot-spots in end-gas autoignition with effects of negative temperature coefficients: Relevance to pressure wave developments
Terashima, Hiroshi, Matsugi, Akira, Koshi, Mitsuo
COMBUSTION AND FLAME, 184, 324, 334, ELSEVIER SCIENCE INC, Oct. 2017, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, The present study deals with the mechanisms for the hot-spot formation and pressure wave development associated with end-gas autoignition during knocking combustion of n-heptane/air mixture. The discussion is based on a one-dimensional (1-D) direct numerical simulation, where the compressible Navier-Stokes equations are solved with a detailed chemical kinetic mechanism of n-heptane, involving 373 species and 1071 reactions. The result demonstrates that the first trigger for a hot-spot formation is a compression wave generated by forced autoignition of a hot kernel and its reflection at a wall. The wall reflection of the propagating compression wave periodically produces an instantaneous temperature increase, which leads to the production of a larger amount of chemical species compared to that of other end-gas points. This non-uniform progress of chemical reaction process continues to exist at the wall, although the temperature increase is transient, resulting in faster autoignition and pressure wave generation at the wall. Thus, an important aspect of observing chemistry behaviors rather than temperature is demonstrated on the mechanism of hot-spot formation. The present study further addresses the reactivity of hot-spots on the relevance to pressure wave developments, wherein a zero-dimensional (0-D) ignition problem with pulsed compression waves is introduced. The higher reactivity of n-heptane/air mixture against pulse waves is observed with the faster ignition delay times in lower and higher initial temperature conditions. Conversely, the result at initial temperatures of 750-800 K indicates the lower reactivity with no significant effects of pulse waves on the ignition delay times. This is connected with the fuel characteristics of a negative temperature coefficient. Thus, in the 1-D simulations, a hot-spot with the high reactivity enhances spatial temperature difference in the end-gas region, leading to strong pressure wave generations. In contrast, a hot-spot with the low reactivity suppresses the pressure wave development with little spatial variation in temperature. The result demonstrates a significant aspect of hot-spot formation and reactivity on pressure wave development during knocking combustion. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

詳細化学反応機構を用いた流体シミュレーション技術とその適用に関する研究
寺島洋史
日本燃焼学会誌, 59, 189, 149‐150, 150, Combustion Society of Japan, Aug. 2017, [Lead author, Corresponding author]
Japanese

Diffusive-thermal effect on local chemical structures in premixed hydrogen-air flames
Matsugi, Akira, Terashima, Hiroshi
COMBUSTION AND FLAME, 179, 238, 241, ELSEVIER SCIENCE INC, May 2017, [Peer-reviewed]
English, Scientific journal, The diffusive-thermal effect plays an important role in the intrinsic instability of premixed flames. A two-dimensional direct numerical simulation of the propagation of premixed hydrogen-air flames was performed using a detailed chemical kinetics model. The cellular behavior of a lean hydrogen-air flame was analyzed on the basis of its chemical structure. The primary consequence of the diffusive-thermal effect was found to be a change in the buildup process of reactive intermediates by the chain reaction mechanism at the preheat zone. The resultant chemical structure at the main reaction zone can be explained by the local composition change of the gas flowing into the reaction zone from the preheat zone. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

ERENA: A fast and robust Jacobian-free integration method for ordinary differential equations of chemical kinetics
Youhi Morii, Hiroshi Terashima, Mitsuo Koshi, Taro Shimizu, Eiji Shima
JOURNAL OF COMPUTATIONAL PHYSICS, 322, 547, 558, ACADEMIC PRESS INC ELSEVIER SCIENCE, Oct. 2016, [Peer-reviewed]
English, Scientific journal, We herein propose a fast and robust Jacobian-free time integration method named as the extended robustness-enhanced numerical algorithm (ERENA) to treat the stiff ordinary differential equations (ODEs) of chemical kinetics. The formulation of ERENA is based on an exact solution of a quasi-steady-state approximation that is optimized to preserve the mass conservation law through use of a Lagrange multiplier method. ERENA exhibits higher accuracy and faster performance in homogeneous ignition simulations compared to existing popular explicit and implicit methods for stiff ODEs such as VODE, MTS, and CHEMEQ2. We investigate the effects of user-specified threshold values in ERENA, to provide trade-off information between the accuracy and the computational cost. (C) 2016 Elsevier Inc. All rights reserved.

Characteristics of Jet-Mixing at Supercritical Pressure: Effects of Recess Length and Post Height
MUTO Daiki, TERASHIMA Hiroshi, TSUBOI Nobuyuki
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 14, 30, Pa_45, Pa_52, THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2016, [Peer-reviewed]
English, Scientific journal,

Effects of injector geometries on cryogenic co-flowing planar jets under a supercritical pressure are numerically investigated. The present study covers a wide range of injector exit geometries which focuses post lip height and recess length, and evaluates these effects on mixing characteristics. A hybrid ILES/RANS methodology is applied to simulate wall-bounded injector regions. The results show that thicker post lips generate larger vortices behind the post lip, resulting the comb-like structure of the rolled-up inner dense jet. As a result, the mixing is well improved, and the inner jet potential core is shortened. The recessed injectors additionally induce a large-scale flapping motion of the inner jet and further enhance the mixing. The frequency analysis with velocity fluctuations demonstrates that the vortex shedding behind the post lip has a frequency which depends on the post lip height. The recessed injectors induce another low-frequency peak of the flapping motion, and which value is independent of the post lip height.

Interface-tracking simulationsof droplet vaporization and burning of hypergolic propellants
Hiroumi Tani, Yutaka Umemura, Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
54th AIAA Aerospace Sciences Meeting, 2016
International conference proceedings, The vaporization and burning of the N2H4 and NTO droplets were simulated with the interface-tracking method to accurately explore the auto-ignition processes and the flame structures. The N2H4 vapor plume developed behind the N2H4 droplet and reacted with the ambient NO2 gas through the hydrogen abstraction reactions. Thus, the N2H4 vapor and NO2 gas mixtures behind the droplet were preheated and reached the auto-ignition at a few ms. The auto-ignition occurred in the multiple points almost at the same time. After the ignition, the premixed flame developed around the droplet. Thus, the vaporization of the liquid N2H4 near the surface became significant. Then, the double flame structures which comprise the inner decomposition flame and oxidation flame appeared around the droplet. The NTO droplet was not auto-ignited in the computational time of the present study because little N2O4 vapor near a saturated temperature decomposed to NO2 gas which is necessary for the hydrogen abstraction reactions. When the ignition was forced, the double flames developed. The outer decomposition flame propagated to the boundaries of the computational domain, while the inner oxidation flame appeared near the droplet. Except for the propagation of the decomposition flame, the NTO droplet combustion was similar to that of the industrial fuels.

Three-dimensional structures in hypergolic ignition process and flame holding mechanisms for hydrazine/nitrogen dioxide un-like doublet impinging gas jets
Yu Daimon, Hiroumi Tani, Hiroshi Terashima, Mitsuo Koshi
54th AIAA Aerospace Sciences Meeting, 2016
International conference proceedings, Hydrazine (N2H4)/nitrogen dioxide (NO2) un-like doublet impinging gas jets were simulated to explore the hypergolic ignition processes in a N2H4/N2O4 bipropellant thruster. The three-dimensional compressible Navier-Stokes equations with a detailed chemical kinetics mechanism, in which more than 200 chemical reactions were directly taken into account, were solved to reveal the influence of the chemical reaction. The differences of three-dimensional structures of hypergolic ignition process and mechanism of flame holding between the two different inlet gas temperatures of 400 and 600 K were discussed in order to investigate the influence of the induction time of chemical reaction on the three-dimensional flowfield. The computed results clarified that the ignition time of impinging gas jets can be significantly influenced by the ignition delay of the detailed chemical kinetics mechanism. In addition, the intermittent multi-ignitions played a significant role in the mechanism of flame holding.

Numerical simulation of jet mixing in a recessed coaxial injector at supercritical pressure
Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi
54th AIAA Aerospace Sciences Meeting, 2016
International conference proceedings, Three-dimensional numerical simulations of cryogenic coaxial jets under supercritical pressure are performed with flushed and recessed injectors to investigate the effect of a recess on the coaxial mixing. A hybrid ILES/RANS method is applied to simulate wallbounded injectors and a recessed region. The recessed injector enhances the density decay and the temperature increase on the central axis, indicating the improvement of mixing compared with the flushed injector. However, the mixing improvement by the recess is not significant in the present conditions. The recess also induces distinct vortex rings around the outer jet. The power spectra of the velocity fluctuations also demonstrated that the low-frequency velocity fluctuations are clearly induced by the recess which frequency corresponds to the large vortex structures.

Generations of unstable combustion in a non-premixed GCH4/GOX rocket injector
H. Terashima, Y. Daimon
52nd AIAA/SAE/ASEE Joint Propulsion Conference, 2016, 2016
International conference proceedings, A two-dimensional detailed numerical simulation is performed for combustion flow field of a GCH4/GOX single injector using detailed chemical kinetics with the compressible Navier-Stokes equations. A detailed mechanism of CH4, 33 chemical species and 150 re- actions, is efficiently and directly introduced. The result shows that the relatively high- temperature and CH4-rich recirculation region is established in the upper and lower corners of the combustion chamber. The result, with a at inlet profile, interestingly shows the generation of an unstable combustion mode, which is not observed with a smooth inlet pro- file. It is shown that the disappearance of non-premixed flames behind the GOX post is a trigger for the unstable combustion mode through the production of partly premixed gases and the generation of autoignition at several locations in the combustion chamber, which may be caused by the extent of the incursion of GCH4 and GOX jets in the recirculation region behind the GOX post.

A robust and accurate numerical method for transcritical turbulent flows at supercritical pressure with an arbitrary equation of state
Soshi Kawai, Hiroshi Terashima, Hideyo Negishi
JOURNAL OF COMPUTATIONAL PHYSICS, 300, 116, 135, ACADEMIC PRESS INC ELSEVIER SCIENCE, Nov. 2015, [Peer-reviewed]
English, Scientific journal, This paper addresses issues in high-fidelity numerical simulations of transcritical turbulent flows at supercritical pressure. The proposed strategy builds on a tabulated look-up table method based on REFPROP database for an accurate estimation of non-linear behaviors of thermodynamic and fluid transport properties at the transcritical conditions. Based on the look-up table method we propose a numerical method that satisfies high-order spatial accuracy, spurious-oscillation-free property, and capability of capturing the abrupt variation in thermodynamic properties across the transcritical contact surface. The method introduces artificial mass diffusivity to the continuity and momentum equations in a physically-consistent manner in order to capture the steep transcritical thermodynamic variations robustly while maintaining spurious-oscillation-free property in the velocity field. The pressure evolution equation is derived from the full compressible Navier-Stokes equations and solved instead of solving the total energy equation to achieve the spurious pressure oscillation free property with an arbitrary equation of state including the present look-up table method. Flow problems with and without physical diffusion are employed for the numerical tests to validate the robustness, accuracy, and consistency of the proposed approach. (C) 2015 Elsevier Inc. All rights reserved.

High-Speed Visualization of Liquid Atomization Phenomena in Sparkling Fireworks
井上智博, 渡辺紀徳, 姫野武洋, 越光男, 寺島洋史
微粒化, 24, 82, 61, 67, 日本液体微粒化学会, Jul. 2015, [Peer-reviewed]
Japanese

Computational Study of the Rate Coefficients for the Reactions of NO2 with CH3NHNH, CH3NNH2, and CH2NHNH2
Nozomu Kanno, Hiroumi Tani, Yu Daimon, Hiroshi Terashima, Norihiko Yoshikawa, Mitsuo Koshi
JOURNAL OF PHYSICAL CHEMISTRY A, 119, 28, 7659, 7667, AMER CHEMICAL SOC, Jul. 2015, [Peer-reviewed]
English, Scientific journal, The reactions of NO2 with cis-/trans-CH3NHNH, CH3NNH2 and CH2NHNH2 have been studied theoretically by quantum chemical calculations and steady-state unimolecular master equation analysis based on RRKM theory. The barrier heights for the roaming transition states between nitro (RNO2) and nitrite (RONO) isomerization reactions and those for the concerted HONO and HNO2 elimination reactions from RNO2 and RONO, affect the pressure dependences of the product-specific rate coefficients. At ambient temperature and pressure, the dominant product of the reactions of NO2 with cis-/trans-CH3NHNH and CH2NHNH2 would be expected to be HONO with trans-CH3NNH and CH2NNH2, respectively, whereas it is CH3N(NH2)NO2 for CH3NNH2 + NO2. The product-specific rate coefficients for the titled and related reactions on the same potential energy surfaces were proposed for kinetics modeling.

Mechanisms of strong pressure wave generation in end-gas autoignition during knocking combustion
Hiroshi Terashima, Mitsuo Koshi
COMBUSTION AND FLAME, 162, 5, 1944, 1956, ELSEVIER SCIENCE INC, May 2015, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, A knocking combustion modeled using a one-dimensional constant volume reactor is simulated in a manner of direct numerical simulations, in which large detailed chemical kinetic mechanisms for two pre-mixed gases, n-butane (113 species) and n-heptane (373 species), are directly and efficiently introduced. Detailed mechanisms of strong pressure wave generation during end-gas autoignition are clarified. Comparison of n-butane and n-heptane shows that the presence of the negative temperature coefficient (NTC) region significantly influences not only the timing of knocking occurrence but also the amplitude of pressure oscillations. In the case of n-heptane with the condition of an adiabatic wall, there is one large peak produced in the strength of knocking intensity for initial temperature between 450 and 1000 K, whereas there is no peak produced in the case of n-butane. The peak generated around 650 K is attributed to a pressure wave intensified through propagation in the end-gas, which is locally generated near the wall with the influence of the NTC region. It is also found that there is a transition of the autoignition position in the end-gas region from the wall for higher initial temperatures to the region ahead of the flame front for lower initial temperatures, leading to different mechanisms of knocking intensity generation. In the case of the isothermal wall condition, the peak around 650 K is reduced due to the lack of a local temperature increase at the wall, demonstrating the influence of wall temperature conditions on the strength of knocking intensity. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Numerical study of the effect of obstacles on the spontaneous ignition of high-pressure hydrogen
Youhi Morii, Hiroshi Terashima, Mitsuo Koshi, Taro Shimizu
JOURNAL OF LOSS PREVENTION IN THE PROCESS INDUSTRIES, 34, 92, 99, ELSEVIER SCI LTD, Mar. 2015, [Peer-reviewed]
English, Scientific journal, A numerical simulation of the spontaneous ignition of high-pressure hydrogen in a duct with two obstacles on the walls is conducted to explore the spontaneous ignition mechanisms. Two-dimensional rectangular ducts are adopted, and the Navier Stokes equations with a detailed chemical kinetic mechanism are solved by using direct numerical simulations. In this study, we focus on the effects of the initial pressure of hydrogen and the position of the obstacles on the ignition mechanisms. Our results demonstrate that the presence of obstacles significantly changes the spontaneous ignition mechanisms producing three distinct ignition mechanisms. In addition, the position of the obstacles drastically changes the interaction of shock waves with the contact surface, and spontaneous ignition may take place at a relatively low pressure in some obstacle positions, which is attributed to the propagation direction and interaction timing of two reflected shock waves. (C) 2015 Elsevier Ltd. All rights reserved.

Unique Flame Dynamics of Spray Combustion of Hypergolic Propellants
谷 洋海, 寺島 洋史, 黒瀬 良一
微粒化シンポジウム講演論文集, 24, 29, 33, 日本液体微粒化学会, Jan. 2015
Japanese

Corrigendum to "Approach for simulating gas-liquid-like flows under supercritical pressures using a high-order central differencing scheme" [J. Comput. Phys., 231, 20, (2012), 6907-6923]Doi: 10.1016/j.jcp.2012.06.021
Hiroshi Terashima, Mitsuo Koshi
Journal of Computational Physics, 283, 609, 610, Academic Press Inc., 2015
English, Scientific journal

Hypergolic ignition mechanism of hydrazine/nitrogen tetroxide co-flowing jets at low temperatures
Hiroumi Tani, Hiroshi Terashima, Yu Daimon, Mitsuo Koshi
International Journal of Energetic Materials and Chemical Propulsion, 14, 1, 71, 84, Begell House Inc., 2015, [Peer-reviewed]
English, Scientific journal, Hydrazine (N2H4)/nitrogen tetroxide (NTO) co-flowing jets were simulated to explore the hypergolic ignition processes in N2H4/NTO bipropellant thrusters. The Navier–Stokes equations with a detailed chemical kinetics mechanism were solved by direct numerical simulation to reveal the influence of the distinct chemical reaction
i.e., hydrogen abstraction by nitrogen dioxide (NO2). In the ignition processes, the hydrogen abstraction sequence, especially the reaction of N2H3 and NO2, played a significant role in preheating the mixture gases and it was significant in the NTO-rich conditions rather than in the specifically stoichiometric conditions. Thus, in the N2H4/NTO co-flowing jets, the preheated regions correspond to the regions where the NTO-rich flows existed and contacted the N2H4 jet. The ignition eventually occurred in the region where NTO has sufficient concentration. Hence, it was found that the ignition timing and position strongly depend on whether the unsteady behavior of the NTO jet provides appropriate environments for the hydrogen abstraction reactions.

Hypergolic ignition and flame structures of hydrazine/nitrogen tetroxide co-flowing plane jets
Hiroumi Tani, Hiroshi Terashima, Mitsuo Koshi, Yu Daimon
PROCEEDINGS OF THE COMBUSTION INSTITUTE, 35, 2199, 2206, ELSEVIER SCIENCE INC, 2015, [Peer-reviewed]
English, Scientific journal, Hydrazine (N2H4)/nitrogen tetroxide (NTO) co-flowing plane jets were simulated to explore the hypergolic ignition processes and flame structures in N2H4/NTO bipropellant thrusters. The Navier-Stokes equations with a detailed chemical kinetics mechanism were solved in a manner of direct numerical simulation to reveal the influence of the distinct chemical reaction, i.e., hydrogen abstraction by nitrogen dioxide (NO2) and the thermal decomposition of N2H4. In the ignition processes, the hydrogen abstraction sequence played a significant role in preheating the mixture gases. Further, the ignition eventually occurred in the region where both N2H4 and NTO were sufficiently supplied for preheating. Hence, the ignition position and delay strongly depended on the fluid-mixing conditions. After the flames reached a steady state, the combustion flames uniquely comprised two types of flames, the outer diffusion flame and the inner decomposition flame. The outer diffusion flame came from the oxidization by NTO. The inner decomposition flame was caused and maintained by the heat transfer from the outer diffusion flame and a high rate of heat release from the thermal decomposition of N2H4. Because of the decomposition flame, the decomposition products such as NH3 and H-2 were the major constituents of the downstream combustion gases. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A robust multi-time scale method for stiff combustion chemistry
Hiroshi Terashima, Youhi Morii, Mitsuo Koshi
International Journal of Energetic Materials and Chemical Propulsion, 14, 3, 177, 196, 2015, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, © 2015 by Begell House, Inc. A robust explicit time integration method for stiff chemical reaction equations is proposed and applied to zero-dimensional ignition and one-dimensional combustion flow problems. The proposed method based on a multi-time scale method significantly improves the robustness of the original method by introducing two new strategies: automatic adjustment of time step size for each characteristic group using a quasi-steady-state assumption and automatic reset of base time step size using two appropriate criteria. The results for several zero-dimensional ignition problems demonstrate the robustness and accuracy of the proposed method compared to existing explicit and implicit integration methods. The present study also provides a computational cost estimation of various terms in the governing equations using a one-dimensional combustion problem (knocking simulation), where the Navier– Stokes equations are coupled with the chemical reaction equations. As well as the zero-dimensional problems, the robustness and capability of the proposed method are demonstrated. While the proposed method alleviates the occupancy of chemical reaction part in the total computational cost compared to an implicit time integration method, it is found that the transport properties calculations relatively increase with considerable amounts, suggesting efficient modeling of transport properties calculations for multi-dimensional combustion problems.

Numerical Simulation on Soot Formation in Diesel Combustion by Using a CFD Code Combined with a Parallelized Explicit ODE Solver
Akira Kikusato, Kazuya Kogo, Beini Zhou, Kusaka Jin, Yasuhiro Daisho, Kiyotaka Sato, Hidefumi Fujimoto, Hiroshi Terashima, Youhi Morii
SAE Technical Papers, 2014-October, 13 Oct. 2014, [Peer-reviewed]
International conference proceedings, Copyright © 2014 SAE International. The objective of the present study is to analyze soot formation in diesel engine combustion by using multi-dimensional combustion simulations with a parallelized explicit ODE solver. Parallelized CHEMEQ2 was used to perform detailed chemical kinetics in KIVA-4 code. CHEMEQ2 is an explicit stiff ODE solver developed by Mott et al. which is known to be faster than traditional implicit ODE solvers, e.g., DVODE. In the present study, about eight times faster computation was achieved with CHEMEQ2 compared to DVODE when using a single thread. Further, by parallelizing CHEMEQ2 using OpenMP, the simulations could be run not only on calculation servers but also on desktop machines. The computation time decreases with the number of threads used. The parallelized CHEMEQ2 enabled combustion and emission characteristics, including detailed soot formation processes, to be predicted using KIVA-4 code with detailed chemical kinetics without the need for reducing the reaction mechanism. After validating the code, diesel engine combustion was simulated to investigate combustion and emission characteristics, focusing on soot formation, growth and oxidation at different EGR ratios. To predict soot formation, a gas-phase polycyclic aromatic hydrocarbons (PAH) precursor formation model was coupled with a detailed phenomenological particle formation model, which included soot nucleation from precursors, surface growth/oxidation and particle coagulation. The results indicate that increased soot emission at high EGR ratios is mainly caused by decreased oxidation by oxygen and OH radicals because mixing fuel and gases (including oxygen and OH) has significant effects on reducing the mass of soot.

Theoretical Study of the Rate Coefficients for CH3NHNH2+NO2 and Related Reactions
Nozomu Kanno, Hiroshi Terashima, Yu Daimon, Norihiko Yoshikawa, Mitsuo Koshi
INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, 46, 8, 489, 499, WILEY-BLACKWELL, Aug. 2014, [Peer-reviewed]
English, Scientific journal, The kinetics and mechanisms of H atom abstraction reactions from CH3NHNH2 by NO2 (R1) and related reactions have been investigated theoretically by using B97X-D and CCSD(T)-F12 quantum chemical calculations and the steady-state unimolecular master equation analysis based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory. For reaction (R1), both dissociation and isomerization steps between intermediate complexes were found to be important for the distribution of the dissociated bimolecular products. The dominant products of (R1) were found to be cis-CH3NHNH and HONO at lower temperature. The branching ratios for CH3NNH2 formation paths increased with increasing temperature. On the same reaction potential energy surface, six reactions including isomerization reactions between CH3NNH2 and cis-/trans-CH3NHNH catalyzed by HONO were suggested to compete with the reverse reaction of (R1). The temperature- and pressure-dependent rate expressions are proposed for kinetic modeling.

Comparison of Time Integration Methods for Stiff Reaction Equations
森井雄飛, 寺島洋史, 越光男, 清水太郎
日本燃焼学会誌, 56, 176, 156, 165, 日本燃焼学会, May 2014, [Peer-reviewed]
Japanese, Scientific journal

Chemical Kinetics of Hypergolic Ignition in N2H4/N2O4-NO2 Gas Mixtures
Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
JOURNAL OF PROPULSION AND POWER, 30, 3, 707, 716, AMER INST AERONAUTICS ASTRONAUTICS, May 2014, [Peer-reviewed]
English, Scientific journal, A detailed chemical kinetic mechanism for hypergolic ignition of N2H4 in a N2O4-NO2 gas mixture has been constructed. In this mechanism, the hypergolic ignition is mainly caused by the sequential reactions of H atom abstraction from N2Hm by NO2: N2Hm + NO2 = N2Hm-1 HONO/HNO2 (m = 4 similar to 1). Although the first step of the H atom abstraction (m = 4) is endothermic, consecutive abstraction reactions for m = 3, 2, and I are exothermic, and especially heat release by the reaction of N2H + NO2 = N-2 + HONO(m =1) is large because of N-2 production. Temperature rise caused by the heat release accelerates the endothermic initiation reaction (m = 4). This thermal feedback is responsible for the hypergolic ignition at low temperatures. Because no experimental and theoretical information is available on these reactions, rate coefficients were evaluated on the basis of transition state theory, unimolecular rate theory, and master equation analysis with quantum chemical calculations of potential energy curves. In addition, reactions of N2H4 with N2O4 isomers were also examined. The present kinetic mechanism can explain gas-phase hypergolic ignition of N2H4/NTO mixtures at temperatures down to 200 K.

Effects of initial diaphragm shape on spontaneous ignition of high-pressure hydrogen in a two-dimensional duct
Hiroshi Terashima, Mitsuo Koshi, Chika Miwada, Toshio Mogi, Ritsu Dobashi
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 39, 11, 6013, 6023, PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2014, [Peer-reviewed]
English, Scientific journal, A two-dimensional (2-D) simulation of spontaneous ignition of high-pressure hydrogen in a length of duct is conducted to explore ignition mechanisms. The present study adopts a 2-D rectangular duct and focuses on effects of the initial diaphragm shape on spontaneous ignition. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. The detailed mechanisms of spontaneous ignitions are discussed for each initial diaphragm shape. For a straight diaphragm, ignition only occurs near the wall owing to the adiabatic wall condition, while three ignition events are identified for a greatly deformed diaphragm: ignition due to reflection of leading shock wave at the wall, hydrogen penetration into shock-heated air near the wall, and deep penetration of hydrogen into shock-heated air behind the leading shock wave. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Numerical study on mixing characteristics of coaxial cryogenic N2/H2 injection under supercritical pressure　　　　　　　　　　　　　　　
Hiroshi Terashima, Mitsuo Koshi
52nd Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics Inc., 2014
English, International conference proceedings, Three-dimensional simulations for nitrogen/hydrogen mixing of a shear coaxial injector under supercritical pressures are conducted in order to investigate their mixing characteristics. A high-order numerical method based on a sixth-order compact scheme is applied. The present study parametrically covers two pressures of 4 and 8 MPa and two outer hydrogen jet conditions, while an inner nitrogen jet condition and a mixture ratio are kept to be same. The discussions on mean and fluctuation properties in addition to instantaneous flow fields are made in order to characterize mixing features for the coaxial injection. A colder outer hydrogen jet provides less mixing behavior compared to a warmer hydrogen jet, generating a longer dense-core of the inner nitrogen jet
unmixed nitrogen and hydrogen remain in downstream regions. Some unique features are found in the temperature profiles on the centerline of inner nitrogen jet as a flattened or a wave-like profile under 4 MPa, while no such unique features are not observed under 8 MPa. In the case of a warmer outer hydrogen jet, the hydrogen density show a maximum peak just after the injection because of the heat transfer to the inner nitrogen jet. The density and temperature fluctuation distributions are determined by the unique thermodynamic fluid variations around the critical temperature, and the velocity and temperature differences among two jets and chamber fluid. Finally, a clear dependence of dense-core length on the momentum flux ratio is demonstrated on comparison with experimental and computational data.

Numerical Analysis on Unsteady Cavitation by Direct Interface Tracking Approach
ISHIKAWA Katsutoshi, UMEMURA Yutaka, HIMENO Takehiro, WATANABE Toshinori, TANI Naoki, TERASHIMA Hiroshi, KOSHI Mitsuo
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 12, 29, Pa_63, Pa_69, THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2014, [Peer-reviewed]
English, Scientific journal, Cavitation may cause a severe damage to rocket engine turbo-pump, and appropriate handling of cavitation is one of the key technologies for rocket engine development. Numerical simulation is quite useful technique, however, simulation result strongly relies on cavitation model. Cavitation flow is essentially strong unsteady and multi scale phenomena, scales of bubbles vary in size from small to large. Therefore, prediction of cavitation by numerical simulation is difficult. Many cavitation models have been proposed and researched. However, direct interface tracking approach has not been applied to cavitating flow and the model characteristic is not fully understood. This research shows direct interface tracking method can properly capture both cloud cavitation and super cavitation and grid resolution affects lift coefficient.

Fast and robust time integration method for stiff chemical kinetic ODEs
Youhi Morii, Hiroshi Terashima, Mitsuo Koshi, Taro Shimizu, Eiji Shima
50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference 2014, 2014
International conference proceedings, © 2014 by authors. Published by the American Institute of Aeronautics and Astronautics, Inc. A simple yet robust and fast time integration method is proposed for efficiently solving stiff chemical kinetic ordinary differential equations. The proposed method is based on a general formula which preserves the conservation laws for any integration operators con- structed using the Lagrange multiplier method. A quasi-steady-state approxixmation is used as the integrator. The time step size is automatically controlled by using a Lagrange multiplier so that the error, which is caused by the Lagrange multiplier method, is small. The results of several ignition problems demonstrate the robustness and accuracy of the proposed method in comparison with other integration methods such as a implicit inte- gration method (VODE), a multi time-scalse method (MTS), and a modified CHEMEQ2. The proposed method, named ERENA, provides the fastest performance for the most of conditions used in this study.

Numerical Study of Real Gas Effects on Shock Tube Problems
Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 12, ists29, Po_2_39-Po_2_44, Po_2_44, THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2014, [Peer-reviewed]
English, Scientific journal, Investigations of real gas effects of supercritical fluids on shock tube problems were numerically performed. Understandings of fluid behaviors under supercritical conditions are essential for the design of high pressure combustors. We developed a numerical code for simulations of flow fields under the supercritical conditions. Cubic types of equation of state are applied to evaluate properties of nearcritical and supercritical fluids. The present code was tested on shock tube problems, and the present result agreed well with a reference result. Comparisons of results between the real gas equations of state and the ideal gas equation of state showed differences in position of shock waves, contact discontinuities, and expansion fans due to the specific thermodynamic features of the supercritical fluids. In a condition that crosses the critical point, the results showed a large density jump with a small temperature jump at the contact discontinuity because of drastic changes of thermodynamic properties. This indicated that the real gas effects obviously appear when the initial condition is close to the critical point of the working fluids.

Consistent numerical diffusion terms for simulating compressible multicomponent flows
Hiroshi Terashima, Soshi Kawai, Mitsuo Koshi
Computers and Fluids, 88, 484, 495, 15 Dec. 2013, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, An interface-capturing method using a high-order central difference scheme is presented for simulations of compressible multicomponent flows. The present method adds consistent numerical diffusion terms to robustly capture interface discontinuities, while maintaining the velocity, pressure, and temperature equilibriums at interfaces. Analysis of the numerical errors generated at the interfaces leads to a proposal of new consistent numerical diffusion terms. The method solves a fully conservative form of the total mass, momentum, total energy, and species-mass, and an additional advection form of the specific heats ratio to preserve the pressure oscillation-free property at the interfaces. Several one- and two-dimensional problems are used to verify the proposed method. © 2013 Elsevier Ltd.

Development and Assessment of an Efficient Method for Simulating Compressible Reacting Flows with Large Detailed Chemical Kinetics
寺島洋史, 越光男
日本燃焼学会誌, 55, 174, 411, 421, 日本燃焼学会, Nov. 2013, [Peer-reviewed], [Lead author, Corresponding author]
Japanese, Scientific journal

Unique characteristics of cryogenic nitrogen jets under supercritical pressures
Hiroshi Terashima, Mitsuo Koshi
Journal of Propulsion and Power, 29, 6, 1328, 1336, Nov. 2013, [Peer-reviewed], [Lead author]
English, Scientific journal, Two-dimensional planar and three-dimensional round nitrogen jets under supercritical pressures are simulated with a wide range of conditions to explore their unique characteristics. A high-order method using a sixth-order compact scheme is applied. The present study parametrically covers two supercritical pressures of 4 and 8 MPa and three jet injection temperatures between a cryogenic jet of 82Kand a warmer jet of 133 K. Unique characteristics are found in both the mean temperature and temperature fluctuation profiles on the centerline (i.e., slower increase of jet temperature and relatively weak temperature fluctuation), only in the case of a near-critical pressure of 4 MPa and a cryogenic jet of 82 K. For the condition, the temperature profile on the centerline uniquely consists of four characteristic regions. The other conditions show no distinct features. The present study suggests that the distributions of the specific heat capacity at constant pressure help to explain the generation of the unique temperature characteristics. Copyright © 2013 by the von Karman Institute for Fluid.

Origin of droplets in sparkling fireworks
Chihiro Inoue, Mitsuo Koshi, Hiroshi Terashima, Takehiro Himeno, Toshinori Watanabe
Science and Technology of Energetic Materials, 74, 3-4, 106, 111, JAPAN EXPLOSIVES SOC, Nov. 2013, [Peer-reviewed]
English, Scientific journal, The physics behind the beauty of sparkling fireworks has not been clarified yet due to a lack of detailed visualization results. In the present study, atomization process in sparkling fireworks is elucidated by using a high-speed video camera. In the first-half sequence of the fireworks, the fireball repeatedly expands, bursts, and shrinks due to the high pressure gas inside the fireball. In contrast, in the last-half sequence, the bubbly fireball slightly deforms, and small bubbles burst on the fireball. A scenario of droplets generation is as follows : a liquid thread extends from the bottom of the bursting fireball, and fragments into droplets. Thus the droplets originate from inside the fireball rather than from its surface.

Strategy for simulating supercritical cryogenic jets using high-order schemes
Hiroshi Terashima, Mitsuo Koshi
Computers and Fluids, 85, 39, 46, 01 Oct. 2013, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, This study presents a strategy for simulations of cryogenic single-species jets under supercritical pressure conditions. In this strategy, a pressure evolution equation is introduced and numerical diffusion terms are consistently constructed in order to maintain the pressure and velocity equilibriums at fluid interfaces. By taking the idea of the equilibrium, the interfaces with high density and temperature ratio are robustly captured without the generation of spurious oscillations, while a high-order central differencing scheme resolves the flow fields. The present method preserves the mass and momentum conservation properties, while the poor energy conservation property is recognized. The one-dimensional interface advection and two-dimensional cryogenic jet mixing problems demonstrate the superiority and robustness of the present method over a conventional fully conservative approach. © 2012 Elsevier Ltd.

Origin of droplets in sparkling fireworks
INOUE Chihiro, KOSHI Mitsuo, TERASHIMA Hiroshi, HIMENO Takehiro, WATANABE Toshinori
Science and technology of energetic materials : Journal of the Japan Explosives Society, 74, 3, 106, 111, 火薬学会, Aug. 2013, [Peer-reviewed]
Japanese, Scientific journal, The physics behind the beauty of sparkling fireworks has not been clarified yet due to a lack of detailed visualization results. In the present study, atomization process in sparkling fireworks is elucidated by using a high-speed video camera. In the first-half sequence of the fireworks, the fireball repeatedly expands, bursts, and shrinks due to the high pressure gas inside the fireball. In contrast, in the last-half sequence, the bubbly fireball slightly deforms, and small bubbles burst on the fireball. A scenario of droplets generation is as follows : a liquid thread extends from the bottom of the bursting fireball, and fragments into droplets. Thus the droplets originate from inside the fireball rather than from its surface.

Origin of hypergolic ignition of N2H4/NO2 mixtures
Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
Science and Technology of Energetic Materials, 74, 1-2, 17, 22, JAPAN EXPLOSIVES SOC, Jul. 2013, [Peer-reviewed]
English, Scientific journal, Hydrazine (N2H4) has a unique characteristic inducing hypergolic ignition even at very low temperatures with nitrogen dioxide (NO2). In order to understand the chemical kinetic origin of this hypergolic nature, thermochemical data (heat of formation, specific heat capacity, and entropy) for chemical species relevant to N2H 4/NO2 combustion are firstly evaluated on the basis of quantum chemical calculation at the CBS-QB3 level of theory. Then, a preliminary detailed chemical kinetic mechanism for gas-phase combustion of N 2H4/NO2 mixtures has been constructed. Kinetic simulations indicated that sequential reactions of N2H m+NO2 (m=4,3,2,l), that is, N2H 4+NO2=N2H3+HONO (1), N 2H3H-NO2=N2H3NO 2= N2H2H-HONO (2), N2H 2+NO2=NNH+HONO (3), and NNH+NO2=N 2+HONO (4), are responsible for the hypergolic ignition at low temperatures. Rate constants of these reactions were estimated based on the transition state theory and unimolecular rate theory. The proposed mechanism can predict low temperature ignition of N2H4/NO 2mixtures. The origin of the low temperature ignition is the reaction sequence of hydrogen abstraction by NO2 from N2H 4, N2H4=>N2H3= >N2H2=>NNH=>N2, Large amount of heat is released during this reaction sequence, especially by the reaction (4) which produces N2, and the resulting temperature rise accelerates the reaction (1), which has a small activation barrier.

Characterization of cryogenic nitrogen jet mixings under supercritical pressures
Hiroshi Terashima, Mitsuo Koshi
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, American Institute of Aeronautics and Astronautics Inc., 2013
English, International conference proceedings, Two-dimensional planar and three-dimensional round nitrogen jets under supercritical pressures are simulated with a wide range of conditions in order to explore its unique characteristics. A high-order method using a sixth-order compact scheme is applied. The present study parametrically covers two supercritical pressures of 4 MPa and 8 MPa and three jet injection temperatures between a cryogenic jet of 82 K and a warmer jet of 133 K. Unique characteristics are found in both the mean temperature and the temperature fluctuation profiles on the centerline, i.e., slower increase of jet temperature and relatively weak temperature fluctuation, only in case of a near-critical pressure of 4 MPa and a cryogenic jet of 82 K. The temperature profile on the centerline of the cryogenic jet of 82 K under 4 MPa uniquely consists of four characteristic regions. The other conditions show no distinct features. The present study suggests that the distributions of the specific heat capacity at constant pressure help to explain the generation of the unique characteristics on the temperature. © 2013 by the authors.

Chemical kinetics of hypergolic ignition in hydrazine/nitrogen-dioxide gas mixtures
Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, 2013
International conference proceedings, A detailed chemical kinetic mechanism for hypergolic ignition of N2H4/NO2 gas mixture at low temperatures has been constructed. In this mechanism, the hypergolic ignition is caused by following sequential reactions of H atom abstraction from N2Hm by NO2. N2H4+ NO2= N2H3+ HONO or HNO2(R1) N2H3+ NO2= N2H2+ HONO (R2) N2H2+ NO2= N2H + HONO (R3) N2H + NO2= N2+ HONO (R4) These reactions are exothermic, especially heat release by the reaction (R4) is large because of N2 production. Temperature rise caused by the heat release accelerates the initiation reaction (R1). This 'thermal feedback' is responsible to the hypergolic ignition at ambient temperatures. Since no experimental and theoretical information was available on these reactions, rate coefficients were evaluated on the basis of transition state theory, uni-molecular rate theory, and master equation analysis with quantum chemical calculations of potential energy curves. Results of simulations by using the present mechanism including reactions (R1)-(R4) reasonably agree with existing experimental data. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Approach for simulating gas-liquid-like flows under supercritical pressures using a high-order central differencing scheme
Hiroshi Terashima, Mitsuo Koshi
JOURNAL OF COMPUTATIONAL PHYSICS, 231, 20, 6907, 6923, ACADEMIC PRESS INC ELSEVIER SCIENCE, Aug. 2012, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, This study proposes an approach for simulations of cryogenic fluid mixing under supercritical pressures using high-order schemes. In this approach, we introduce a pressure evolution equation and consistently construct numerical diffusion terms to maintain the velocity and pressure equilibriums at fluid interfaces. The interfaces with high density and temperature ratio are successfully captured without the generation of spurious oscillations, while a high-order central differencing scheme resolves the flow fields. The present method preserves the mass and momentum conservation properties, while the poor energy conservation property is recognized. The one-dimensional single and multi-species interface advection and two-dimensional cryogenic jet mixing problems demonstrate the superiority and robustness of the present method over a conventional fully conservative method. (C) 2012 Elsevier Inc. All rights reserved.

Numerical (error) issues on compressible multicomponent flows using a high-order differencing scheme: Weighted compact nonlinear scheme
Taku Nonomura, Seiichiro Morizawa, Hiroshi Terashima, Shigeru Obayashi, Kozo Fujii
JOURNAL OF COMPUTATIONAL PHYSICS, 231, 8, 3181, 3210, ACADEMIC PRESS INC ELSEVIER SCIENCE, Apr. 2012, [Peer-reviewed]
English, Scientific journal, A weighted compact nonlinear scheme (WCNS) is applied to numerical simulations of compressible multicomponent flows, and four different implementations (fully or quasi-conservative forms and conservative or primitive variables interpolations) are examined in order to investigate numerical oscillation generated in each implementation. The results show that the different types of numerical oscillation in pressure field are generated when fully conservative form or interpolation of conservative variables is selected, while quasi-conservative form generally has poor mass conservation property. The WCNS implementation with quasi-conservative form and interpolation of primitive variables can suppress these oscillations similar to previous finite volume WENO scheme, despite the present scheme is finite difference formulation and computationally cheaper for multi-dimensional problems. Series of analysis conducted in this study show that the numerical oscillation due to fully conservative form is generated only in initial flow fields, while the numerical oscillation due to interpolation of conservative variables exists during the computations, which leads to significant spurious numerical oscillations near interfaces of different component of fluids. The error due to fully conservative form can be greatly reduced by smoothing interface, while the numerical oscillation due to interpolation of conservative variables cannot be significantly reduced. The primitive variable interpolation is, therefore, considered to be better choice for compressible multicomponent flows in the framework of WCNS. Meanwhile better choice of fully or quasi-conservative form depends on a situation because the error due to fully conservative form can be suppressed by smoothed interface and because quasi-conservative form eliminates all the numerical oscillation but has poor mass conservation. (C) 2012 Elsevier Inc. All rights reserved.

Approach to prevent spurious oscillations in compressible multicomponent flows using high-order methods
Hiroshi Terashima, Soshi Kawai, Mitsuo Koshi
American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM, 1, 635, 643, 2012
English, International conference proceedings, We present an interface-capturing method for fluid interfaces in compressible multicomponent flows using high-order central-difference-based schemes. Numerical diffusion terms are consistently designed so that the velocity, pressure, and temperature equilibriums are maintained at the fluid interfaces, while serving as an efficient interface-capturing. Advection problems of a contact discontinuity and a material interface shows that 1) the present method maintains the velocity, pressure, and temperature equilibriums at the fluid interfaces (oscillation-free property) and 2) the numerical diffusion terms effectively works for suppressing spurious wiggles of the density or temperature. Comparisons with a conventional fully-conservative approach demonstrates the superiority of the present method in avoiding spurious oscillations. A shock tube problem of two-component gases shows the capability for capturing the shock wave while the velocity and pressure equilibriums are successfully maintained at the contact discontinuity. Copyright © 2012 by ASME.

High-Resolution Numerical Method for Supercritical Flows with Large Density Variations
Hiroshi Terashima, Soshi Kawai, Nobuhiro Yamanishi
AIAA JOURNAL, 49, 12, 2658, 2672, AMER INST AERONAUTICS ASTRONAUTICS, Dec. 2011, [Peer-reviewed]
English, Scientific journal, A high-resolution methodology using a high-order compact differencing scheme with localized artificial diffusivity is introduced with the aim of simulating jet mixing under supercritical pressure environments. The nonlinear localized artificial diffusivity provides the stability to capture different types of discontinuity, such as shock wave, contact surface, and material interface, whereas the high-order compact difference scheme resolves broadband scales in the rest of the domain. The present method is tested on several one-dimensional discontinuity-related problems under super/transcritical conditions and a comparatively more illustrative two-dimensional low-temperature planar jet problem under a supercritical pressure condition. The localized artificial diffusivity, especially artificial thermal conductivity for temperature gradients, effectively suppresses numerical wiggles near the interfaces. The effects of the artificial thermal conductivity on numerical stability and accuracy are examined. Comparisons between the present method and a conventional low-order scheme demonstrate the superior performance of the present method for resolving a wide range of flow scales while successfully capturing large density/temperature variations at interfaces.

A high-resolution scheme for compressible multicomponent flows with shock waves
Soshi Kawai, Hiroshi Terashima
INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, 66, 10, 1207, 1225, WILEY-BLACKWELL, Aug. 2011, [Peer-reviewed]
English, Scientific journal, A simple methodology for a high-resolution scheme to be applied to compressible multicomponent flows with shock waves is investigated. The method is intended for use with direct numerical simulation or large eddy simulation of compressible multicomponent flows. The method dynamically adds non-linear artificial diffusivity locally in space to capture different types of discontinuities such as a shock wave, contact surface or material interface while a high-order compact differencing scheme resolves a broad range of scales in flows. The method is successfully applied to several one-dimensional and two-dimensional compressible multicomponent flow problems with shock waves. The results are in good agreement with experiments and earlier computations qualitatively and quantitatively. The method captures unsteady shock and material discontinuities without significant spurious oscillations if initial start-up errors are properly avoided. Comparisons between the present numerical scheme and high-order weighted essentially non-oscillatory (WENO) schemes illustrate the advantage of the present method for resolving a broad range of scales of turbulence while capturing shock waves and material interfaces. Also the present method is expected to require less computational cost than popular high-order upwind-biased schemes such as WENO schemes. The mass conservation for each species is satisfied due to the strong conservation form of governing equations employed in the method. Copyright (C) 2010 John Wiley & Sons, Ltd.

Investigations of trans/supercritical jet mixing using a high-resolution numerical method
Hiroshi Terashima, Soshi Kawai, Nobuhiro Yamanishi
41st AIAA Fluid Dynamics Conference and Exhibit, American Institute of Aeronautics and Astronautics Inc., 2011
English, International conference proceedings, Two-dimensional planar nitrogen jets in supercritical thermodynamic conditions are simulated using a high-resolution numerical method (which consists of a sixth-order compact difference scheme and a localized artificial diffusivity method) with the aim at exploring its unique characteristics. Effects of injection temperature, chamber pressure, and the equation of state on supercritical jet behaviors are investigated. Throughout the investigations, two major unique characteristics are found under the transcritical conditions. One unique characteristic are found in the mean temperature profile, as the slower increase of jet temperature, in the case of transcritical injections. The cause for the unique feature is simply explained by the corresponding temperature-density (T-ρ) diagrams. Another unique feature of supercritical jet flows appears in the generation of different flow scales. The power spectrums and the flow fields quantitatively and qualitatively show the different features of flow scales due to the injection conditions. In the transcritical injection, the production of smaller flow scales is considerably enhanced relative to the other injection cases, due to not only its higher density ratio, but also its abrupt variations (leap) of δρ/δT in the T-ρ diagrams. This study indicates, for the present conditions used, that the unique characteristics of supercritical jet flows appear in the mean temperature distributions and the generation of different flow scales, which are simply yet effectively explained by the T-ρ diagrams. © 2011 by the authors.

A front-tracking method with projected interface conditions for compressible multi-fluid flows
Hiroshi Terashima, Gretar Tryggvason
COMPUTERS & FLUIDS, 39, 10, 1804, 1814, PERGAMON-ELSEVIER SCIENCE LTD, Dec. 2010, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, A front-tracking method for compressible multi-fluid flows is presented, where marker points are used both for tracking fluid interfaces and also for constructing the Riemann problem on the interfaces. The Riemann problem between the two fluid phases (defined in the interface normal direction) is solved using the exact Riemann solver on the marker points. The solutions are projected onto fixed grid points and then extrapolated into the corresponding ghost-fluid regions, to be used as boundary conditions. Each fluid phase is solved separately as in the ghost-fluid method. The proposed procedures, especially the projection of the exact Riemann solutions onto the fluid grids, are designed to be simple and consistent in any spatial dimensions. Several multi-fluid problems, including the breakup of a water cylinder induced by the passage of a shock wave were computed in order to demonstrate the capability of the proposed method. (C) 2010 Elsevier Ltd. All rights reserved.

A front-tracking/ghost-fluid method for fluid interfaces in compressible flows
Hiroshi Terashima, Gretar Tryggvason
JOURNAL OF COMPUTATIONAL PHYSICS, 228, 11, 4012, 4037, ACADEMIC PRESS INC ELSEVIER SCIENCE, Jun. 2009, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, A front-tracking/ghost-fluid method is introduced for simulations of fluid interfaces in compressible flows. The new method captures fluid interfaces using explicit front-tracking and defines interface conditions with the ghost-fluid method. Several examples of multi-phase flow simulations, including a shock-bubble interaction. the Richtmyer-Meshkov instability, the Rayleigh-Taylor instability, the collapse of an air bubble in water and the breakup of a water drop in air, using the Euler or the Navier-Stokes equations, are performed in order to demonstrate the accuracy and capability of the new method. The computational results are compared with experiments and earlier computational studies. The results show that the new method can simulate interface dynamics accurately, including the effect of surface tension. Results for compressible gas-water systems show that the new method can be used for simulations of fluid interface with large density differences. (C) 2009 Elsevier Inc. All rights reserved.

Transonic aeroelastic computations of a delta wing configuration with high fidelity equations
Hiroshi Terashima, Kenji Ono
Computational Fluid Dynamics 2006 - Proceedings of the Fourth International Conference on Computational Fluid Dynamics, ICCFD 2006, 843, 848, 2009
International conference proceedings

Reliability of compressible flow/structure coupling method on Cartesian grid with signed distance field
Hiroshi Terashima, Kenji Ono
2007 Proceedings of the 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007, 1 SYMPOSIA, PART A, 219, 228, 2007
International conference proceedings, A compressible flow solver coupled with moving/deformed geometries on Cartesian grid with Signed Distance Field (SDF) is developed and its capability is investigated through computations of several basic flow fields for future applications with certain reliability. The flow solver is designed so that SDF includes sufficient geometrical information to compute flow fields. Since information of moving/deformed geometries is recognized as a change of the SDF between time steps, the flow solver can be coupled with moving/deformed geometries naturally. The implementation of this solver is simple and easy. No modification is needed in the main part of the flow solver. Furthermore, the interpolation and the corresponding stencils searching process are not required. Several basic flow fields around fixed/moving cylinders and a fixed sphere are computed in order to validate the proposed solver, in which the computed results are compared with available numerical and experimental results. The results demonstrated the method's capability for moderate Reynolds number flows around both of fixed and moving geometries. Based on the results, some criteria and problems for obtaining reliable solution are suggested. Copyright © 2007 by ASME.

Reliability of compressible flow/structure coupling method on Cartesian grid with signed distance field
Hiroshi Terashima, Kenji Ono
FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B, 219, 228, AMER SOC MECHANICAL ENGINEERS, 2007
English, International conference proceedings, A compressible flow solver coupled with moving/deformed geometries on Cartesian grid with Signed Distance Field (SDF) is developed and its capability is investigated through computations of several basic flow fields for future applications with certain reliability. The flow solver is designed so that SDF includes sufficient geometrical information to compute flow fields. Since information of moving/deformed geometries is recognized as a change of the SDF between time steps, the flow solver can be coupled with moving/deformed geometries naturally. The implementation of this solver is simple and easy. No modification is needed in the main part of the flow solver. Furthermore, the interpolation and the corresponding stencils searching process are not required. Several basic flow fields around fixed/moving cylinders and a fixed sphere are computed in order to validate the proposed solver, in which the computed results are compared with available numerical and experimental results. The results demonstrated the method's capability for moderate Reynolds number flows around both of fixed and moving geometries. Based on the results, some criteria and problems for obtaining reliable solution are suggested.

Influence of stores on the transonic flutter of a delta wing configuration
Hiroshi Terashima, Kozo Fujii
AIAA JOURNAL, 45, 1, 237, 246, AMER INST AERONAUT ASTRONAUT, Jan. 2007, [Peer-reviewed], [Lead author, Corresponding author]
English, Scientific journal, Transonic and supersonic flutter characteristics of a delta wing configuration with external stores were computationally simulated, and the aerodynamic influence of the stores on the flutter characteristics was investigated. Delta wings with one and two external stores were considered. Unsteady aerodynamics of the wing with external stores were evaluated using Navier-Stokes equations, and equations of motion based on a modal approach were applied to the structural dynamics. These equations were,coupled using a subiteration approach. The computational results showed that the flutter dynamic pressures were reduced for a wide range of Mach numbers when the external stores were attached. The flutter dynamic pressures also decreased as the number of external stores increased. In the case of one external store, the aerodynamic influence of the store could be divided into two regions according to the Mach number. It was found that neglecting the aerodynamic influence of the store led to an overestimation of the flutter dynamic pressures in the supersonic flow region. In the case of two external stores, the aerodynamic influence of the stores on the flutter boundary appeared only at one supersonic Mach number, unlike the case of one external store. Additional flutter analysis using a different store size and unsteady aerodynamic analysis with forced oscillations indicated that the interference position of the shock wave generated ahead of the external store on the lower surface was a key factor in determining the flutter boundary, and the shock wave oscillation may have acted as a negative damping on the wing motion.

Effect of the time stepping size in the implicit method for transonic flutter simulations
Hiroshi Terashima, Kozo Fujii
Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 71, 712, 2856, 2863, Japan Society of Mechanical Engineers, 2005, [Peer-reviewed], [Lead author, Corresponding author]
Japanese, Scientific journal, One criterion that determines time stepping size in the implicit time integration method is given for accurate and effective transonic flutter simulations. Transonic flows over two-dimensional forced oscillating airfoils with several reduced frequencies are first investigated for constructing a criterion for selecting the time stepping size, and then two and three-dimensional transonic flutter simulations are performed for evaluating the criterion. Results for the forced oscillating airfoil indicate that unsteady aerodynamic forces converge in a constant value as the time stepping size decreases and the time stepping size required the convergence of unsteady aerodynamic force depends on the reduced frequency. From these results, it turns out that 4 000 integration steps during one cycle of airfoil oscillations are enough for the estimation of the unsteady aerodynamic forces at any reduced frequency. The time stepping size is automatically decided by setting 4 000 integration steps during one cycle of airfoil oscillations. Results for two and three-dimensional transonic flutter simulations show that flutter boundaries can be accurately and effectively calculated based on the criterion.

Effects of number of stores on the transonic flutter characteristics of a delta wing configuration
Hiroshi Terashima, Kozo Fujii
34th AIAA Fluid Dynamics Conference and Exhibit, American Institute of Aeronautics and Astronautics Inc., 2004
English, International conference proceedings, Transonic and supersonic flutter characteristics of a delta wing configuration with external stores are simulated using the fluid/structure coupling method and the effect of the store aerodynamics is investigated. A delta wing with one and two external stores are considered in this study. The stores are located in the rearward of the wing simulating typical high speed aircraft configurations. The computational result shows that the flutter dynamic pressures over all the Mach numbers are reduced by adding external stores for both cases. In addition, the flutter dynamic pressures become much lower when the number of attached external stores is increased. In the case of the single external store, influence of the store aerodynamics can be divided into two regions according to the Mach number. It is found that neglecting the store aerodynamics leads to the overestimation of the flutter dynamic pressures in the supersonic region. In case of two external stores, the store aerodynamics influence on the flutter boundary only at M∞ = 1.22 unlike the case of the single external store. It is shown that the shock wave ahead of the external store influences on the pressure distributions on the lower surface and the location of the shock wave is important for the decision of the flutter boundary. © 2004 by the American Institute of Aeronautics and Astronautics, Inc.

Numerical Estimations of Transonic Flutter Phenomena with Fluid/Structure Coupling Method
TERASHIMA Hiroshi, FUJII Kozo
The proceedings of the JSME annual meeting, 2002, 293, 294, The Japan Society of Mechanical Engineers, 2002
Japanese, Symposium, Flutter phenomena for the AGARD445.6 standard aeroelastic wing in the transonic flow are simulated using the fluid/structure coupling method. The effect of time accuracy, number of the inner-iterations and comparison of a fully implicit coupling method with a loosely coupling method are examined. The sufficient number of inner-iterations in time is required for the accurate prediction of time responses when using a large time step. Improvement of the solution time accuracy for the aerodynamic equations is key for accurate aeroelastic computations and the one-step time lag generated in a loosely coupling method does not have an effect in the flutter prediction in transonic flows.

『富岳』燃焼シミュレーションに向けての数値モデルと計算法—Numerical Models and Methods for Combustion Simulation on FUGAKU Class Supercomputer—特集 燃焼科学における大規模数値シミュレーションの最前線
大島 伸行, 寺島 洋史, 日本燃焼学会誌 = Journal of the Combustion Society of Japan, 64, 208, 136, 143, May 2022
日本燃焼学会, Japanese

Accelerating the calculation of supercritical non-ideal thermal and transport property models using deep learning
KAWARAI Yuki, TERASHIMA Hiroshi, The Proceedings of Mechanical Engineering Congress, Japan, 2022, J061-03, 2022
Fluids under supercritical conditions exhibit unique physical properties that differ from those under subcritical conditions or standard temperature and pressure conditions. For this reason, when performing numerical simulations of fluids under supercritical conditions, the fluid cannot be treated as an ideal gas, and it is necessary to consider the non-ideal property of the fluid. However, if a simulation is performed considering the non-ideal property of the fluid, more computation time is required compared to the case where the fluid is treated as an ideal gas. To reduce the computational cost if non-ideal properties, we developed a mathematical model that can estimate fluid properties considering non-idealities using deep learning, and by replacing it with a conventional method, we confirmed that the calculation speed can be accelerated while maintaining the calculation accuracy of the conventional method in a multi-component flow field under supercritical conditions., The Japan Society of Mechanical Engineers, Japanese

Study on Aerodynamic Instability Mitigation for Hayabusa-type Reentry Capsule using Proper Orthogonal Decomposition
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 衝撃波シンポジウム講演論文集(CD-ROM), 2019, 2020

A mechanism for injection coupled combustion instabilities of an H2/O2 rocket-type combustor
太田徹, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 34th, 2020

Flame Holding/Extinguishing Mechanisms for Ammonia and Methane Laminar Non-premixed Jet Flames
大江真央, 寺島洋史, 林潤, 赤松史光, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 34th, 2020

Numerical investigation of transonic flutter for supercritical airfoils: comparison with conventional symmetric airfoils
三宅冬馬, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 34th, 2020

Flame holding/extinguishing mechanisms for ammonia and methane laminar non-premixed jet flames
大江真央, 寺島洋史, 林潤, 赤松史光, 大島伸行, 燃焼シンポジウム講演論文集(CD-ROM), 58th, 2020

A localized thickened flame model: 定容容器内火炎伝播及び末端ガス自着火現象への適用
寺島 洋史, 河合 宗司, ながれ, 38, 435, 438, 2019

アンモニア拡散バーナー火炎の保炎/消炎機構に関する詳細反応CFD解析
大江真央, 寺島洋史, 林潤, 赤松史光, 大島伸行, 日本伝熱シンポジウム講演論文集(CD-ROM), 56th, 2019

The Relationship between Wake Flow of the HAYABUSA Type Reentry Capsule and Aerodynamic Stability
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 宇宙科学技術連合講演会講演集(CD-ROM), 63rd, 2019

はやぶさ型再突入カプセルまわりの流れ場とカプセル表面圧力の関係
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 33rd, 2019

超低軌道における膜面展開型超小型衛星のポストフライト解析
齊藤雅弘, 高橋裕介, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 33rd, 2019

ロケットエンジンH₂/O₂燃焼流れ場に対する噴射器リセス長さの影響
太田徹, 村上峻, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 33rd, 2019

翼端板付加による翼端近傍流れ場及び誘導抵抗への影響
今井啓太, 寺島洋史, 坪倉誠, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 33rd, 2019

Chamber pressure effects on the combustion flow structure behind a splitter plate of a rocket injector
村上峻, 寺島洋史, 大島伸行, 燃焼シンポジウム講演論文集(CD-ROM), 57th, 2019

Numerical investigation of tulip flame formation considering detailed chemistry
ARAKI Kengo, TERASHIMA Hiroshi, The Proceedings of the Fluids engineering conference, 2018, OS9-5, 2018
The present study numerically investigates the formation mechanism of a tulip-shaped flame observed in a high aspect ratio rectangular channel. The compressible Navier-Stokes equations are solved with a detailed chemical kinetics mechanism of hydrogen. The result indicates that a first trigger for the tulip flame formation is a vortex generation near the left end-wall during the initial stage of a finger-shaped flame development. A large vortex structure produced in the burnt region interacts with the propagating flame front and the vortex-induced acceleration and deceleration of the flame front consequently forms the tulip-shaped flame. The interaction of pressure waves with the flame front affects a flame instability and flame propagation behavior. However, the flame instability may have no significant influence on the formation of tulip-shaped flame in the present condition., The Japan Society of Mechanical Engineers, Japanese

Aerodynamic Simulation for HAYABUSA Type Reentry Capsule in Transonic Regime
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 50th-36th, 2018

Dynamics of shock wave and separation region over a forced oscillating airfoil in the transonic flow regime
榎並聖也, 寺島洋史, 高橋裕介, 大島伸行, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 50th-36th, 2018

Aerodynamic Instability Analysis of HAYABUSA Type Reentry Capsule
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 宇宙科学技術連合講演会講演集(CD-ROM), 62nd, 2018

A numerical study for the mechanism of tulip-typed flame propagation in a high aspect ratio rectangular channel
荒木謙吾, 寺島洋史, 大島伸行, 燃焼シンポジウム講演論文集, 56th, 2018

ロケット噴射器近傍に形成される燃焼流れ場構造:H2/O2とCH4/O2の比較
村上峻, 寺島洋史, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 32nd, 2018

Aerodynamic Instability Analysis of HAYABUSA Type Reentry Capsule
鶴本徹, 高橋裕介, 寺島洋史, 大島伸行, 日本機械学会流体工学部門講演会講演論文集(CD-ROM), 96th, 2018

Aerodynamic stability of flare-type thin-membrane inflatable aeroshell in suborbital reentry
大橋達志, 高橋裕介, 寺島洋史, 大島伸行, 日本機械学会流体工学部門講演会講演論文集(CD-ROM), 96th, 2018

観測ロケットを用いた柔軟構造体の再突入試験における空力不安定性解析
大橋達志, 松永学, 高橋裕介, 寺島洋史, 大島伸行, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 49th-35th, 2017

柔軟構造体に対する再突入ブラックアウトの数値解析
榎尚也, 松永学, 高橋裕介, 寺島洋史, 大島伸行, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 49th-35th, 2017

衝撃波はく離を伴う遷音速強制振動翼周りの非定常流れ場構造と空力予測について
榎並聖也, 寺島洋史, 高橋裕介, 大島伸行, 数値流体力学シンポジウム講演論文集(CD-ROM), 31st, 2017

Numerical simulation for effects of pressure on cryogenic coaxial jet under supercritical pressure
Takahide Araki, Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi, AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting, 2017
Three-dimensional numerical simulations of coaxial nitrogen jet mixing under supercritical pressures are performed with an emphasis on the effects of pressure on the mixing. The results show that the overall mixing behaviors are similar in terms of normalized density profiles between 5 and 12 MPa. However, the normalized temperature profiles are different between two conditions because non-linear change of the density to the temperature near the critical point. The peak of the constant pressure specific heat is particularly observed in the case of 5 MPa. The density and temperature fluctuations become large between the inner jet flow and the outer jet flow. Although the density fluctuation distributions are similar between two cases, the larger fluctuation region of temperature is observed in the case of 5 MPa. This is because the temperature increases are different near the critical temperature between two pressure conditions., American Institute of Aeronautics and Astronautics Inc., English

反応性流体シミュレーションの新展開
越光男, 寺島洋史, 谷洋海, 大門優, 衝撃波シンポジウム講演論文集(CD-ROM), 2016, ROMBUNNO.TOKUベTSUKOEN II, 2017
Japanese

燃焼現象 詳細化学反応機構を用いた反応性流体解析における高効率解析手法
森井雄飛, 寺島洋史, 日本ガスタービン学会誌, 44, 2, 96‐101, 101, 18 Mar. 2016
Gas Turbine Society of Japan, Japanese

Detailed flame structure of a high-pressure GCH₄/GOX jet flow behind a GOX post of rocket engines
Terashima Hiroshi, Daimon Yu, The Proceedings of the Thermal Engineering Conference, 2016, D112, 2016
Detailed structures of gaseous CH₄/O₂ combustion flow fields behind a GOX post of rocket engines have been numerically investigated by using the Navier-Stokes equations with a detailed chemical kinetic model. The results show that the two types of combustion flow structures are established in the region behind the GOX post according to CH₄ and O₂ jet injection conditions. A broad higher-temperature region appears with a single anticlockwise recirculation region for larger velocity ratios of CH₄ to O₂ jets, while a lower-temperature region is formed with the presence of non-premixed flame structures and additional generations of another clockwise recirculation region for smaller velocity ratios., The Japan Society of Mechanical Engineers, Japanese

着火遅れ時間特性と末端ガス自着火・圧力波強度の関係:容器圧力条件を変化させたノッキング解析
佐藤伴音, 寺島洋史, 大島伸行, 燃焼シンポジウム講演論文集, 54th, 2016

Effects of Injection Condition on Cryogenic Jet in Cross-flow under Supercritical Pressures
小塚 悟史, 武藤 大貴, 寺島 洋史, 坪井 伸幸, 日本航空宇宙学会西部支部講演会講演集, 5p, 2016
[日本航空宇宙学会西部支部], Japanese

Chemical kinetics of hypergolic ignition for CH3NHNH2/N2O4/NO2 gas mixtures
KANNO Nozomu, KANNO Nozomu, KANIE Yuto, TANI Hiroumi, DAIMON Yu, TERASHIMA Hiroshi, KOSHI Mitsuo, 航空原動機・宇宙推進講演会講演論文集(CD-ROM), 56th, ROMBUNNO.AJCPP2016‐055, 2016
English

Numerical Modeling of Droplet Burning of Hypergolic Propellants
TANI Hiroumi, UMEMURA Yutaka, DAIMON Yu, TERASHIMA Hiroshi, KOSHI Mitsuo, 航空原動機・宇宙推進講演会講演論文集(CD-ROM), 56th, ROMBUNNO.AJCPP2016‐134, 2016
English

A High-resolution and Robust Method for Supercritical Fluids With Large Density Contrasts(Challenges in CFD for Space Program)
Terashima Hiroshi, Journal of the Japan Society for Simulation Technology, 34, 3, 171, 179, 15 Sep. 2015
Japan Society for Simmulation Technology, Japanese

宇宙開発におけるCFDの課題 宇宙機スラスタにおける自燃性推進薬の混合・燃焼場の解明を目指して
大門優, 谷洋海, 寺島洋史, 菅野望, 越光男, 根岸秀世, シミュレーション, 34, 3, 180, 185, 15 Sep. 2015
Japan Society for Simmulation Technology, Japanese

Strong Pressure Wave Generations Induced by Inhomogeneous End-Gas Autoignition
TERASHIMA Hiroshi, Journal of the Combustion Society of Japan, 57, 181, 206, 213, Aug. 2015
The paper sheds light on a fundamental issue of knocking combustion, i.e., mechanisms of pressure wave generations and autoignition in end-gas region. The results from our recent numerical simulations, where a knocking combustion is modeled using a one-dimensional constant-volume reactor, are introduced and discussed with a survey of relevant previous studies. The importance of the negative temperature coefficient on the mechanisms of strong pressure wave generations and the location of autoignition position in end-gas region is clearly highlighted. The paper also presents a strategy for efficiently handing detailed chemical kinetics mechanisms in computational fluid dynamics simulations., Combustion Society of Japan, Japanese

Robust and fast integration method for numerical simulations of reactive flow(Selected Researches in CFD28)
MORII Youhi, TERASHIMA Hiroshi, KOSHI Mitsuo, SHIMIZU Taro, SHIMA Eiji, Journal of Japan Society of Fluid Mechanics, 34, 2, 131, 135, 25 Apr. 2015
日本流体力学会, Japanese

Double flame structure of hydrazine/nitrogen dioxide coaxial jets
谷洋海, 寺島洋史, 越光男, 大門優, 宇宙航空研究開発機構特別資料 JAXA-SP-, 14-010, 75, 80, 25 Mar. 2015
Japanese

Approach for simulating gas-liquid-like flows under supercritical pressures using a high-order central differencing scheme (vol 231, pg 6907, 2012)
Hiroshi Terashima, Mitsuo Koshi, JOURNAL OF COMPUTATIONAL PHYSICS, 283, 609, 610, Feb. 2015
ACADEMIC PRESS INC ELSEVIER SCIENCE, English, Others

爆燃・爆轟伝播現象に対するATF/詳細反応機構を用いたモデリング
森井雄飛, 寺島洋史, 清水太郎, 青野淳也, 燃焼シンポジウム講演論文集, 53rd, 2015

Effects of injector geometry on co-flowing planar jet mixings under supercritical pressures
Daiki Muto, Nobuyuki Tsuboi, Hiroshi Terashima, 53rd AIAA Aerospace Sciences Meeting, 2015
The effects of the injector geometries on co-flowing planar cryogenic jet mixings under a supercritical condition are numerically investigated. The present study focuses the recess of the coaxial injector which is widely applied in practical liquid rocket engines. The present numerical method applies an ILES/RANS hybrid method to simulate the jet mixing in the wall-bounded recessed region. As a validation of the present method, a mono-planar jet and a round jet simulations are carried out, and the results agree well with an experimental result. To examine the effects of the recess length on the coaxial injections, two-dimensional co-planar jet simulations at the supercritical pressure are performed in three recess lengths. The recessed cases show the strong flapping motions of the high densty jet, and as a result, the injected fluids are mixed well compared with the case without the recess. While there is a small difference on the potential core length between the cases without the recess and the shorter recess, the longer recess case largely shortens the jet core., American Institute of Aeronautics and Astronautics Inc, AIAA, English

障害物を含む管内高圧水素放出における自着火メカニズム
森井雄飛, 寺島洋史, 越光男, 清水太郎, 衝撃波シンポジウム講演論文集(CD-ROM), 2013, 2014

大規模詳細反応機構の適用を可能とする高効率反応性流体解析手法の提案
寺島洋史, 森井雄飛, 越光男, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 46th-32nd, 2014

詳細化学反応に並列化陽解法を適用した三次元数値流体解析による高速化とディーゼル微粒子の生成過程に関する研究
喜久里陽, 向後和也, ZHOU Beini, 草鹿仁, 大聖泰弘, 佐藤圭峰, 藤本英史, 寺島洋史, 森井雄飛, 内燃機関シンポジウム講演論文集(CD-ROM), 25th, 2014

反応性流体解析における化学反応方程式の堅牢・高速な時間積分法
森井雄飛, 寺島洋史, 越光男, 清水太郎, 嶋英志, 数値流体力学シンポジウム講演論文集(CD-ROM), 28th, 2014

Numerical Simulation of low-temperature Hydrogen Jet Injected into Supercritical Crossflow
坂井 敦紘, 武藤 大貴, 寺島 洋史, 日本航空宇宙学会西部支部講演会講演集, 4p, 2014
[日本航空宇宙学会西部支部], Japanese

Numerical study of cryogenic coaxial jet under supercritical condition
Daiki Muto, Nobuyuki Tsuboi, Hiroshi Terashima, 52nd Aerospace Sciences Meeting, 01 Jan. 2014
© 2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved. Effects of recess on the mixing of the cryogenic coaxial jet under supercritical conditions were numerically investigated. Recessed injectors have been applied as coaxial injectors of liquid rocket engines because it is expected to improve propellant mixing and combustion efficiency. In the present study, a numerical simulation code was developed to examine jet mixing under the supercritical pressures. For validation of the present method, a two-dimensional planner jet simulation was carried out. The present result showed good agreement with an experimental result. As a preliminary study of coaxial jets, co-planner simulations were performed in a recessed case and an unrecessed case. Large-scale vortical structures were observed in the both cases, and the recessed case showed the larger struc- tures relative to the unrecessed case. This is because of the destabilization mechanism of a recessed region. These instabilities improved entrainments of ambient uid, and as a result, the enhanced jet mixing shortens the jet-core length.

802 Numerical Study of Injector Geometry Effects on Cryogenic Coaxial Jet under Supercritical Conditions
MUTO Daiki, TSUBOI Nobuyuki, TERASHIMA Hiroshi, 日本機械学会九州支部講演論文集, 2014, 67, "802, 1"-"802-2", 2014
The Japan Society of Mechanical Engineers, Japanese

0633 Cryogenic Hydrogen Jet in Cross-flow under Supercritical Pressure
SAKAI Atsuhiro, Mutoh Daiki, TERASHIMA Hiroshi, TSUBOI Nobuyuki, NEGISHI Hideyo, Fluids engineering conference ..., 2013, "0633, 01"-"0633-02", 09 Nov. 2013
This study has investigated numerically the interaction of cryogenic hydrogen jet with heated hydrogen cross flow under supercritical pressures relevant to a mixer component in liquid rocket engines. The mixer is considered to be a key component for achieving high reliability of LE-X engine, where an expander bleed cycle is adopted. A two-dimensional simulation of hydrogen jet in cross flow under a supercritical pressure is first performed to explore mixing characteristics in a wide range of injection conditions. Effects of injection temperature and therefore momentum flux ratio on the hydrogen jet in cross flow are comprehensively investigated. A high-order numerical method for the Navier-Stokes equations with a real-fluid equation of state is used for resolving highly unsteady flow fields with large density gradients., The Japan Society of Mechanical Engineers, Japanese

A fast and efficient method for simulations of reacting flows with large detailed chemical kinetics: application of a dynamic multi-timescale method
TERASHIMA HIROSHI, KOSHI MITSUO, MORII YUHI, 宇宙航空研究開発機構特別資料 JAXA-SP-, 12-010, 49, 54, 29 Mar. 2013
44th Fluid Dynamics Conference / Aerospace Numerical Simulation Symposium 2012 (July 5-6, 2012. Toyama International Conference Center), Toyama JapanA dynamic multi-timescale (MTS) method is introduced to a well-validated computational fluid dynamic (CFD) solver, aiming at development of a fast and efficient method for simulations of reacting with large detailed chemical kinetics. The performance capability of the MTS method are validated for several reaction systems and a wide range of pressure and temperature conditions, showing its accuracy and dramatic reduction of computational time, relative to a conventional direct integration method (VODE). Shock tube problems are used to examine the performance of the MTS method on the CFD solver, demonstrating its potential of handling reactive flow simulations with large detailed chemical kinetics efficiently.Physical characteristics: Original contains color illustrations, 宇宙航空研究開発機構(JAXA), Japanese

Effect of injection temperatures and pressures on supercritical jet characteristics
TERASHIMA HIROSHI, KOSHI MITSUO, 宇宙航空研究開発機構特別資料 JAXA-SP-, 12-010, 207, 212, 29 Mar. 2013
Japanese

713 Investigation of Influence of Pressure on Two-dimensional Supercritical Jet Flows Using Numerical Simulation
SAKAI Atsuhiro, MUTOH Daiki, TERASHIMA Hiroshi, TSUBOI Nobuyuki, 日本機械学会九州支部講演論文集, 2013, 66, 223, 224, 13 Mar. 2013
The Japan Society of Mechanical Engineers, Japanese

716 Effects of Equation of State on Shock Tube Simulation under Supercritical Condition
MUTOH Daiki, TSUBOI Nobuyuki, TERASHIMA Hiroshi, 日本機械学会九州支部講演論文集, 2013, 66, 229, 230, 13 Mar. 2013
The Japan Society of Mechanical Engineers, Japanese

流体との連成を可能とする大規模反応方程式高速時間積分法の評価
森井雄飛, 寺島洋史, 越光男, 清水太郎, 自動車技術会学術講演会前刷集, 158-13, 2013

詳細な素反応過程を考慮したエンジン燃焼シミュレーション-常微分方程式の高速数値解法の検証-
佐藤圭峰, 藤本英史, 寺島洋史, 草鹿仁, 森井雄飛, 燃焼シンポジウム講演論文集, 51st, 2013

流体解析における化学反応方程式のシンプルかつロバストな高速時間積分法
森井雄飛, 寺島洋史, 越光男, 清水太郎, 燃焼シンポジウム講演論文集, 51st, 2013

管内高圧水素放出に誘起される自着火現象の数値解析
寺島洋史, 森井雄飛, 越光男, 茂木俊夫, 土橋律, 数値流体力学シンポジウム講演論文集(CD-ROM), 27th, 2013

線香花火における微粒化現象の可視化
井上智博, 渡辺紀徳, 姫野武洋, 越光男, 寺島洋史, 微粒化シンポジウム講演論文集, 22nd, 2013

気液界面の直接捕獲による非定常キャビテーションと内部流動について
石川勝利, 梅村悠, 姫野武洋, 渡辺紀徳, 谷直樹, 寺島洋史, 越光男, 航空原動機・宇宙推進講演会講演論文集(CD-ROM), 53rd, 2013

Approach for robustly simulating supercritical cryogenic fluids using high-order schemes : extension to multi-species flows
寺島洋史, 越光男, ながれ：日本流体力学誌, 31, 6, 483, 486, Dec. 2012
日本流体力学会, Japanese

Fluids under supercritical pressures(Frontiers in Combustion Research)
TERASHIMA Hiroshi, KOSHI Mitsuo, Journal of Japan Society of Fluid Mechanics, 31, 4, 351, 356, 25 Aug. 2012
Japan Society of Fluid Mechanics, Japanese

Numerical method for satisfying equilibriums at interfaces in compressible multicomponent flows using a high-order compact differencing scheme((Selected Researches in CFD25,Feature Article of 25th CFD Symposium)
TERASHIMA Hiroshi, KAWAI Soshi, KOSHI Mitsuo, Journal of Japan Society of Fluid Mechanics, 31, 2, 131, 139, 25 Apr. 2012
Japan Society of Fluid Mechanics, Japanese

803 Numerical Simulation of Jet Structure Using Preconditioning Unsteady Compressible Method
MUTOH Daiki, SETOGUCHI Akira, TSUBOI Nobuyuki, TERASHIMA Hiroshi, KOSHI Mitsuo, 日本機械学会九州支部講演論文集, 2012, 65, 271, 272, 16 Mar. 2012
The Japan Society of Mechanical Engineers, Japanese

大規模詳細反応を考慮した流体の高速・高効率計算法の開発:ダイナミックマルチタイムスケール法の適用
寺島洋史, 越光男, 森井雄飛, 流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 44th-2012, 2012

線香花火における液滴生成過程の可視化
井上智博, 越光男, 寺島洋史, 渡辺紀徳, 姫野武洋, 火薬学会秋季研究発表講演会講演要旨集, 2012, 2012

メタン酸素及び水素酸素燃料を用いた狭い管内を伝播する爆轟波の二次元数値解析
森井雄飛, 坪井伸幸, 小川博之, 寺島洋史, 徳留真一郎, 林光一, 衝撃波シンポジウム講演論文集, 2011, 2012

高解像度コンパクト差分法を用いた超臨界圧環境下における噴流構造の数値解析—A high-resolution scheme for jet mixing flows under supercritical thermodynamic conditions
寺島, 洋史, Terashima, Hiroshi, 宇宙航空研究開発機構特別資料: 東京大学ロケットエンジンモデリングラボラトリー(JAXA社会連携講座)シンポジウム ロケットエンジン解析技術の新展開後刷集 = JAXA Special Publication: Proceedings of the Symposium on Rocket Engine Modeling Laboratory, the University of Tokyo (JAXA public relations lecture): New Horizon of Rocket Engine Modeling and Simulation, JAXA-SP-10-010, 163, 173, Mar. 2011
東京大学ロケットエンジンモデリングラボラトリー(JAXA社会連携講座)シンポジウム(2010年9月28日-29日. 東京大学)
Symposium on Rocket Engine Modeling Laboratory, University of Tokyo (JAXA public relations lecture): New Horizon of Rocket Engine Modeling and Simulation (September 28-29, 2010. University of Tokyo), Tokyo Japan
形態: カラー図版あり
共催: 東京大学ロケットエンジンモデリングラボラトリー(JAXA社会連携講座), 宇宙航空研究開発機構
Physical characteristics: Original contains color illustrations
Meeting sponsors: Rocket Engine Modeling Laboratory, University of Tokyo (JAXA public relations lecture), JAXA's Engineering Degital Innovation Center, Japan Aerospace Exploration Agency (JAXA)(JEDI)
資料番号: AA0064934010
レポート番号: JAXA-SP-10-010, 宇宙航空研究開発機構, Japanese

Thermo-fluid phenomena related to high-pressure injection of propellant and atomization
Himeno Takehiro, Inoue Chihiro, Miyashita Yosuke, Watanabe Toshinori, Terashima Hiroshi, Negishi Hideyo, 宇宙航空研究開発機構特別資料: 東京大学ロケットエンジンモデリングラボラトリー(JAXA社会連携講座)シンポジウム ロケットエンジン解析技術の新展開後刷集 = JAXA Special Publication: Proceedings of the Symposium on Rocket Engine Modeling Laboratory, the University of Tokyo (JAXA public relations lecture): New Horizon of Rocket Engine Modeling and Simulation, 10, 251, 265, Mar. 2011
Symposium on Rocket Engine Modeling Laboratory, University of Tokyo (JAXA public relations lecture): New Horizon of Rocket Engine Modeling and Simulation (September 28-29, 2010. University of Tokyo), Tokyo JapanPhysical characteristics: Original contains color illustrationsMeeting sponsors: Rocket Engine Modeling Laboratory, University of Tokyo (JAXA public relations lecture), JAXA's Engineering Degital Innovation Center, Japan Aerospace Exploration Agency (JAXA)(JEDI), Japan Aerospace Exploration Agency (JAXA), Japanese

Thermo-fluid phenomena associated with injection and atomization of cryogenic propellant
井上 智博, 寺島 洋史, 根岸 秀世, Aeronautical and space sciences Japan, 58, 677, 185, 191, Jun. 2010
日本航空宇宙学会, Japanese

A front-tracking method with projected interface conditions for compressible multi-fluid flows
TERASHIMA Hiroshi, TRYGGVASON Gretar, 微粒化シンポジウム講演論文集 = Symposium (ILASS-Japan) on Atomization, 18, 95, 101, 16 Dec. 2009
Japanese

距離関数を利用した流体構造連成解析法の信頼性評価
寺島 洋史, 第20回数値流体力学シンポジウム講演要旨集 (CD-ROM), 2006

Software Licensing in the University Environment
KU Katharine, Journal of the Japan Society for Computational Engineering and Science, 9, 2, 900, 902, 30 Apr. 2004
日本計算工学会, Japanese

フラッターシミュレーションに向けた振動翼周り流れの信頼性評価—Numerical analysis of the oscillating airfoil flowfield toward accurate flutter simulations
寺島, 洋史, 藤井, 孝藏, Terashima, Hiroshi, Fujii, Kozo, 航空宇宙技術研究所特別資料: 航空宇宙数値シミュレーション技術シンポジウム2001論文集 = Special Publication of National Aerospace Laboratory: Proceedings of Aerospace Numerical Simulation Symposium 2001, 53, 285, 290, Jan. 2002
Transonic flows over the NACA64A010 airfoil oscillating in pitch about its one-quarter chord are numerically investigated for the assessment of the flow solver to predict the accurate unsteady aerodynamics forces. The effect of the outer boundary region and time accuracy in the implicit method such as LU-SGS time integration method is also described in this paper. Results at Mach number 0.8 over the airfoil oscillating with the reduced frequency of about 0.2 are compared with experimental data, respectively. The computed results with aft-shock attached flow show the importance of the computational domain and the implementation of the inner iteration method to the implicit time integration algorithm. For the case of shock induced separation flows, the computed results disagree with the experimental results due to the effect of the turbulence modeling, even with the increased time accuracy.
資料番号: AA0032819049
レポート番号: NAL SP-53, 航空宇宙技術研究所, Japanese

708 Some problems found in the CFD analysis of Space Transportation Systems
FUJII Kozo, MORIYA Koichiro, TERASHIMA Hiroshi, HORIE Toshiyuki, Fluids engineering conference ..., 2001, 100, 100, 28 Sep. 2001
CFD simulations using three-dimensional compressible Navier-Stokes equations are carried out for the establishment of the reliability of the CFD tools for the aerodynamic evaluation of space transportation systems. Simulations for Apollo-type capsule show that the simulations with typical number of grid points can give us reasonable result and CFD analysis can be a useful tool for the initial estimation of aerodynamic characteristics. Simulations for the FTB configuration show the dependency of the aerodynamic data on the order of accuracy of the simulations. The flow field near the base alters the characteristics. The example for the delta and double-delta wings which may be a candidate for the future TSTO systems shows that the success of the CFD simulations for delta wings does not necessarily justify the CFD results for similar configurations., The Japan Society of Mechanical Engineers, Japanese

High-pressure flows for propulsion applications
Bellan, Josette, American Institute of Aeronautics and Astronautics, Detailed Modeling of Supercritical Jets and Flames, pp. 571–630
American Institute of Aeronautics and Astronautics, 2020, 9781624105807, xiv, 787 p., English

1) 計算力学ハンドブック「第II巻 差分法・有限体積法（熱流体編）」　　　　　　　　　　　　　　　
寺島洋史, 第4章圧縮性流れ第5項連成問題
日本機械学会，丸善, 2006, [Contributor]

A computational study for combustion flow fields of a high-pressure gaseous hydrogen/oxygen coflow jet behind a splitter plate
Shun Murakami, Hiroshi Terashima, Nobuyuki Oshima
AIAA Scitech 2019 Forum, 01 Jan. 2019
© 2019 by Timothy K. Minton. Published by the American Institute of Aeronautics and Astronautics, Inc. A computational study is performed for exploring flow and flame dynamics of a high-pressure hydrogen/oxygen coflow jet with the effects of post thickness and moment flux ratio. A two-dimensional model with a splitter plate, which represents a post configuration of an injector of rocket engines, is adapted to fully resolve the combustion flow field. The compressible Navier-Stokes equations are solved with a detailed chemical kinetic mechanism in a manner of direct numerical simulation. The result shows that the post thickness largely affects the temperature distribution in a recirculation region established behind the post. The temperature distribution is determined with the amount of incoming high-temperature combustion gas and unburned hydrogen gas, which significantly changes with the post thickness. The effect of the momentum flux ratio clearly appears in the case of thicker post configuration, while in the case of thinner post configuration no major differences are identified for all the momentum flux ratio. The study shows a tendency that thicker post geometries with smaller J numbers provide lower temperature fields in the recirculation region behind the post, thus preliminarily indicating some difficulty of maintaining a flame anchoring in the recirculation region.

定容容器におけるエンドガス局所自着火現象の可視化
藤田晴彦, 伊藤祐太朗, 山田眞平, 下栗大右, 佐藤伴音, 寺島洋史, 河野通治, 本田雄哉, 植木義治, 横畑英明
日本伝熱シンポジウム講演論文集(CD-ROM), 2017, Japanese

柔軟構造体に対する再突入ブラックアウトの数値解析
榎尚也, 松永学, 高橋裕介, 寺島洋史, 大島伸行
流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 2017, Japanese

観測ロケットを用いた柔軟構造体の再突入試験における空力不安定性解析
大橋達志, 松永学, 高橋裕介, 寺島洋史, 大島伸行
流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム講演集(CD-ROM), 2017, Japanese

Numerical simulation for effects of pressure on cryogenic coaxial jet under supercritical pressure
Takahide Araki, Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi
AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting, 01 Jan. 2017
© 2017 by Rolls-Royce North America Holdings Inc. Three-dimensional numerical simulations of coaxial nitrogen jet mixing under supercritical pressures are performed with an emphasis on the effects of pressure on the mixing. The results show that the overall mixing behaviors are similar in terms of normalized density profiles between 5 and 12 MPa. However, the normalized temperature profiles are different between two conditions because non-linear change of the density to the temperature near the critical point. The peak of the constant pressure specific heat is particularly observed in the case of 5 MPa. The density and temperature fluctuations become large between the inner jet flow and the outer jet flow. Although the density fluctuation distributions are similar between two cases, the larger fluctuation region of temperature is observed in the case of 5 MPa. This is because the temperature increases are different near the critical temperature between two pressure conditions.

ノッキング現象におけるホットスポットの源について
寺島洋史, 松木亮
燃焼シンポジウム講演論文集, 26 Nov. 2016, Japanese

着火遅れ時間特性と末端ガス自着火・圧力波強度の関係:容器圧力条件を変化させたノッキング解析
佐藤伴音, 寺島洋史, 大島伸行
燃焼シンポジウム講演論文集, 26 Nov. 2016, Japanese

高圧メタン酸素ロケット噴射器近傍の非定常燃焼流れ場構造:詳細反応機構を用いたCFD解析
寺島洋史, 大門優
日本機械学会熱工学コンファレンス講演論文集(CD-ROM), 2016, Japanese

超臨界圧力下における極低温同軸噴流への噴射条件の影響
武藤大貴, 武藤大貴, 寺島洋史, 坪井伸幸
数値流体力学シンポジウム講演論文集(CD-ROM), 2016, Japanese

Interface-tracking simulationsof droplet vaporization and burning of hypergolic propellants
Hiroumi Tani, Yutaka Umemura, Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
54th AIAA Aerospace Sciences Meeting, 01 Jan. 2016
© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA, All rights reserved. The vaporization and burning of the N 2 H 4 and NTO droplets were simulated with the interface-tracking method to accurately explore the auto-ignition processes and the flame structures. The N 2 H 4 vapor plume developed behind the N 2 H 4 droplet and reacted with the ambient NO 2 gas through the hydrogen abstraction reactions. Thus, the N 2 H 4 vapor and NO 2 gas mixtures behind the droplet were preheated and reached the auto-ignition at a few ms. The auto-ignition occurred in the multiple points almost at the same time. After the ignition, the premixed flame developed around the droplet. Thus, the vaporization of the liquid N 2 H 4 near the surface became significant. Then, the double flame structures which comprise the inner decomposition flame and oxidation flame appeared around the droplet. The NTO droplet was not auto-ignited in the computational time of the present study because little N 2 O4 vapor near a saturated temperature decomposed to NO 2 gas which is necessary for the hydrogen abstraction reactions. When the ignition was forced, the double flames developed. The outer decomposition flame propagated to the boundaries of the computational domain, while the inner oxidation flame appeared near the droplet. Except for the propagation of the decomposition flame, the NTO droplet combustion was similar to that of the industrial fuels.

Numerical simulation of jet mixing in a recessed coaxial injector at supercritical pressure
Daiki Muto, Hiroshi Terashima, Nobuyuki Tsuboi
54th AIAA Aerospace Sciences Meeting, 01 Jan. 2016
© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Three-dimensional numerical simulations of cryogenic coaxial jets under supercritical pressure are performed with flushed and recessed injectors to investigate the effect of a recess on the coaxial mixing. A hybrid ILES/RANS method is applied to simulate wallbounded injectors and a recessed region. The recessed injector enhances the density decay and the temperature increase on the central axis, indicating the improvement of mixing compared with the flushed injector. However, the mixing improvement by the recess is not significant in the present conditions. The recess also induces distinct vortex rings around the outer jet. The power spectra of the velocity fluctuations also demonstrated that the low-frequency velocity fluctuations are clearly induced by the recess which frequency corresponds to the large vortex structures.

Three-dimensional structures in hypergolic ignition process and flame holding mechanisms for hydrazine/nitrogen dioxide un-like doublet impinging gas jets
Yu Daimon, Hiroumi Tani, Hiroshi Terashima, Mitsuo Koshi
54th AIAA Aerospace Sciences Meeting, 01 Jan. 2016
© 2016 by the American Institute of Aeronautics, and Astronautics, Inc. All rights reserved. Hydrazine (N 2 H 4 )/nitrogen dioxide (NO 2 ) un-like doublet impinging gas jets were simulated to explore the hypergolic ignition processes in a N 2 H 4 /N 2 O4 bipropellant thruster. The three-dimensional compressible Navier-Stokes equations with a detailed chemical kinetics mechanism, in which more than 200 chemical reactions were directly taken into account, were solved to reveal the influence of the chemical reaction. The differences of three-dimensional structures of hypergolic ignition process and mechanism of flame holding between the two different inlet gas temperatures of 400 and 600 K were discussed in order to investigate the influence of the induction time of chemical reaction on the three-dimensional flowfield. The computed results clarified that the ignition time of impinging gas jets can be significantly influenced by the ignition delay of the detailed chemical kinetics mechanism. In addition, the intermittent multi-ignitions played a significant role in the mechanism of flame holding.

Generations of unstable combustion in a non-premixed GCH4/GOX rocket injector
H. Terashima, Y. Daimon
52nd AIAA/SAE/ASEE Joint Propulsion Conference, 2016, 01 Jan. 2016
© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. A two-dimensional detailed numerical simulation is performed for combustion flow field of a GCH4/GOX single injector using detailed chemical kinetics with the compressible Navier-Stokes equations. A detailed mechanism of CH4, 33 chemical species and 150 re- actions, is efficiently and directly introduced. The result shows that the relatively high- temperature and CH4-rich recirculation region is established in the upper and lower corners of the combustion chamber. The result, with a at inlet profile, interestingly shows the generation of an unstable combustion mode, which is not observed with a smooth inlet pro- file. It is shown that the disappearance of non-premixed flames behind the GOX post is a trigger for the unstable combustion mode through the production of partly premixed gases and the generation of autoignition at several locations in the combustion chamber, which may be caused by the extent of the incursion of GCH4 and GOX jets in the recirculation region behind the GOX post.

Effects of injector geometry on co-flowing planar jet mixings under supercritical pressures
Daiki Muto, Nobuyuki Tsuboi, Hiroshi Terashima
53rd AIAA Aerospace Sciences Meeting, 01 Jan. 2015
© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The effects of the injector geometries on co-flowing planar cryogenic jet mixings under a supercritical condition are numerically investigated. The present study focuses the recess of the coaxial injector which is widely applied in practical liquid rocket engines. The present numerical method applies an ILES/RANS hybrid method to simulate the jet mixing in the wall-bounded recessed region. As a validation of the present method, a mono-planar jet and a round jet simulations are carried out, and the results agree well with an experimental result. To examine the effects of the recess length on the coaxial injections, two-dimensional co-planar jet simulations at the supercritical pressure are performed in three recess lengths. The recessed cases show the strong flapping motions of the high densty jet, and as a result, the injected fluids are mixed well compared with the case without the recess. While there is a small difference on the potential core length between the cases without the recess and the shorter recess, the longer recess case largely shortens the jet core.

Hypergolic ignition and flame structures of hydrazine spray/gaseous nitrogen tetroxide co-flowing jets
Hiroumi Tani, Hiroshi Terashima, Ryoichi Kurose, Tomoaki Kitano, Mitsuo Koshi, Yu Daimon
53rd AIAA Aerospace Sciences Meeting, 01 Jan. 2015
© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Hydrazine (N 2 H 4 ) spray/gaseous nitrogen tetroxide (NTO) co-flowing jets were simulated to explore the hypergolic combustion flows in N 2 H 4 /NTO bipropellant thrusters. The Navier-Stokes equations with the use of a detailed chemical kinetics mechanism and dispersed droplets with evaporation models were solved in a manner of direct numerical simulations. The influence of the evaporation of N 2 H 4 droplets upon the hypergolic ignition processes and flame structures was investigated. Before the auto-ignition, the N 2 H 4 vapor and the ambient NTO gas mixtures were preheated as a result of the hydrogen abstraction reactions, whereas the evaporation of the N 2 H 4 droplets decreased the temperature of the gas mixtures. When the temperature of the NTO flows was sufficiently high, the N 2 H 4 vapor and NTO gas mixtures were preheated and could auto-ignite near the leading edge of the N 2 H 4 spray. This occurred because the heat transfer from the ambient gases to the droplets and the N 2 H 4 vapor enhanced the hydrogen abstraction reactions in the leading edge. After the auto-ignition, the double flame structure appeared, comprising the outer diffusion flames and inner decomposition flame. Interestingly, the inner decomposition flame and the N 2 H 4 vapor flow exhibited a sinusoidal behavior. This behavior was initiated by the locally expanded decomposition gases and developed by the supply of the N 2 H 4 droplets to the decomposition gases at relatively high temperatures. When the droplet size was small, the auto-ignition was not always enhanced because the temperature of the N 2 H 4 vapor and the NTO gas mixtures decreased. Furthermore, the sinusoidal behavior of the inner decomposition flame was less significant because the flame’s development depended on the temperature of the N 2 H 4 vapor and inertial mass of the droplets.

Numerical study on mixing characteristics of coaxial cryogenic N2/H2 injection under supercritical pressure
Hiroshi Terashima, Mitsuo Koshi
52nd Aerospace Sciences Meeting, 01 Jan. 2014
© 2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved. Three-dimensional simulations for nitrogen/hydrogen mixing of a shear coaxial injector under supercritical pressures are conducted in order to investigate their mixing characteristics. A high-order numerical method based on a sixth-order compact scheme is applied. The present study parametrically covers two pressures of 4 and 8 MPa and two outer hydrogen jet conditions, while an inner nitrogen jet condition and a mixture ratio are kept to be same. The discussions on mean and fluctuation properties in addition to instantaneous flow fields are made in order to characterize mixing features for the coaxial injection. A colder outer hydrogen jet provides less mixing behavior compared to a warmer hydrogen jet, generating a longer dense-core of the inner nitrogen jet; unmixed nitrogen and hydrogen remain in downstream regions. Some unique features are found in the temperature profiles on the centerline of inner nitrogen jet as a flattened or a wave-like profile under 4 MPa, while no such unique features are not observed under 8 MPa. In the case of a warmer outer hydrogen jet, the hydrogen density show a maximum peak just after the injection because of the heat transfer to the inner nitrogen jet. The density and temperature fluctuation distributions are determined by the unique thermodynamic fluid variations around the critical temperature, and the velocity and temperature differences among two jets and chamber fluid. Finally, a clear dependence of dense-core length on the momentum flux ratio is demonstrated on comparison with experimental and computational data.

Numerical Simulation on Soot Formation in Diesel Combustion by Using a CFD Code Combined with a Parallelized Explicit ODE Solver
Akira Kikusato, Kazuya Kogo, Beini Zhou, Kusaka Jin, Yasuhiro Daisho, Kiyotaka Sato, Hidefumi Fujimoto, Hiroshi Terashima, Youhi Morii
SAE Technical Papers, 01 Jan. 2014
Copyright © 2014 SAE International. The objective of the present study is to analyze soot formation in diesel engine combustion by using multi-dimensional combustion simulations with a parallelized explicit ODE solver. Parallelized CHEMEQ2 was used to perform detailed chemical kinetics in KIVA-4 code. CHEMEQ2 is an explicit stiff ODE solver developed by Mott et al. which is known to be faster than traditional implicit ODE solvers, e.g., DVODE. In the present study, about eight times faster computation was achieved with CHEMEQ2 compared to DVODE when using a single thread. Further, by parallelizing CHEMEQ2 using OpenMP, the simulations could be run not only on calculation servers but also on desktop machines. The computation time decreases with the number of threads used. The parallelized CHEMEQ2 enabled combustion and emission characteristics, including detailed soot formation processes, to be predicted using KIVA-4 code with detailed chemical kinetics without the need for reducing the reaction mechanism. After validating the code, diesel engine combustion was simulated to investigate combustion and emission characteristics, focusing on soot formation, growth and oxidation at different EGR ratios. To predict soot formation, a gas-phase polycyclic aromatic hydrocarbons (PAH) precursor formation model was coupled with a detailed phenomenological particle formation model, which included soot nucleation from precursors, surface growth/oxidation and particle coagulation. The results indicate that increased soot emission at high EGR ratios is mainly caused by decreased oxidation by oxygen and OH radicals because mixing fuel and gases (including oxygen and OH) has significant effects on reducing the mass of soot.

Fast and robust time integration method for stiff chemical kinetic ODEs
Youhi Morii, Hiroshi Terashima, Mitsuo Koshi, Taro Shimizu, Eiji Shima
50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference 2014, 01 Jan. 2014
© 2014 by authors. Published by the American Institute of Aeronautics and Astronautics, Inc. A simple yet robust and fast time integration method is proposed for efficiently solving stiff chemical kinetic ordinary differential equations. The proposed method is based on a general formula which preserves the conservation laws for any integration operators con- structed using the Lagrange multiplier method. A quasi-steady-state approxixmation is used as the integrator. The time step size is automatically controlled by using a Lagrange multiplier so that the error, which is caused by the Lagrange multiplier method, is small. The results of several ignition problems demonstrate the robustness and accuracy of the proposed method in comparison with other integration methods such as a implicit inte- gration method (VODE), a multi time-scalse method (MTS), and a modified CHEMEQ2. The proposed method, named ERENA, provides the fastest performance for the most of conditions used in this study.

Numerical study of cryogenic coaxial jet under supercritical condition
Daiki Muto, Nobuyuki Tsuboi, Hiroshi Terashima
52nd Aerospace Sciences Meeting, 01 Jan. 2014
© 2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved. Effects of recess on the mixing of the cryogenic coaxial jet under supercritical conditions were numerically investigated. Recessed injectors have been applied as coaxial injectors of liquid rocket engines because it is expected to improve propellant mixing and combustion efficiency. In the present study, a numerical simulation code was developed to examine jet mixing under the supercritical pressures. For validation of the present method, a two-dimensional planner jet simulation was carried out. The present result showed good agreement with an experimental result. As a preliminary study of coaxial jets, co-planner simulations were performed in a recessed case and an unrecessed case. Large-scale vortical structures were observed in the both cases, and the recessed case showed the larger struc- tures relative to the unrecessed case. This is because of the destabilization mechanism of a recessed region. These instabilities improved entrainments of ambient uid, and as a result, the enhanced jet mixing shortens the jet-core length.

Chemical kinetics of hypergolic ignition in hydrazine/nitrogen-dioxide gas mixtures
Yu Daimon, Hiroshi Terashima, Mitsuo Koshi
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, 19 Aug. 2013
A detailed chemical kinetic mechanism for hypergolic ignition of N2H4/NO2 gas mixture at low temperatures has been constructed. In this mechanism, the hypergolic ignition is caused by following sequential reactions of H atom abstraction from N2Hm by NO2. N2H4+ NO2= N2H3+ HONO or HNO2(R1) N2H3+ NO2= N2H2+ HONO (R2) N2H2+ NO2= N2H + HONO (R3) N2H + NO2= N2+ HONO (R4) These reactions are exothermic, especially heat release by the reaction (R4) is large because of N2 production. Temperature rise caused by the heat release accelerates the initiation reaction (R1). This 'thermal feedback' is responsible to the hypergolic ignition at ambient temperatures. Since no experimental and theoretical information was available on these reactions, rate coefficients were evaluated on the basis of transition state theory, uni-molecular rate theory, and master equation analysis with quantum chemical calculations of potential energy curves. Results of simulations by using the present mechanism including reactions (R1)-(R4) reasonably agree with existing experimental data. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Characterization of cryogenic nitrogen jet mixings under supercritical pressures
Hiroshi Terashima, Mitsuo Koshi
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013, 19 Aug. 2013
Two-dimensional planar and three-dimensional round nitrogen jets under supercritical pressures are simulated with a wide range of conditions in order to explore its unique characteristics. A high-order method using a sixth-order compact scheme is applied. The present study parametrically covers two supercritical pressures of 4 MPa and 8 MPa and three jet injection temperatures between a cryogenic jet of 82 K and a warmer jet of 133 K. Unique characteristics are found in both the mean temperature and the temperature fluctuation profiles on the centerline, i.e., slower increase of jet temperature and relatively weak temperature fluctuation, only in case of a near-critical pressure of 4 MPa and a cryogenic jet of 82 K. The temperature profile on the centerline of the cryogenic jet of 82 K under 4 MPa uniquely consists of four characteristic regions. The other conditions show no distinct features. The present study suggests that the distributions of the specific heat capacity at constant pressure help to explain the generation of the unique characteristics on the temperature. © 2013 by the authors.

Approach to prevent spurious oscillations in compressible multicomponent flows using high-order methods
Hiroshi Terashima, Soshi Kawai, Mitsuo Koshi
American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM, 01 Dec. 2012
We present an interface-capturing method for fluid interfaces in compressible multicomponent flows using high-order central-difference-based schemes. Numerical diffusion terms are consistently designed so that the velocity, pressure, and temperature equilibriums are maintained at the fluid interfaces, while serving as an efficient interface-capturing. Advection problems of a contact discontinuity and a material interface shows that 1) the present method maintains the velocity, pressure, and temperature equilibriums at the fluid interfaces (oscillation-free property) and 2) the numerical diffusion terms effectively works for suppressing spurious wiggles of the density or temperature. Comparisons with a conventional fully-conservative approach demonstrates the superiority of the present method in avoiding spurious oscillations. A shock tube problem of two-component gases shows the capability for capturing the shock wave while the velocity and pressure equilibriums are successfully maintained at the contact discontinuity. Copyright © 2012 by ASME.

Investigations of trans/supercritical jet mixing using a high-resolution numerical method
Hiroshi Terashima, Soshi Kawai, Nobuhiro Yamanishi
41st AIAA Fluid Dynamics Conference and Exhibit, 01 Dec. 2011
Two-dimensional planar nitrogen jets in supercritical thermodynamic conditions are simulated using a high-resolution numerical method (which consists of a sixth-order compact difference scheme and a localized artificial diffusivity method) with the aim at exploring its unique characteristics. Effects of injection temperature, chamber pressure, and the equation of state on supercritical jet behaviors are investigated. Throughout the investigations, two major unique characteristics are found under the transcritical conditions. One unique characteristic are found in the mean temperature profile, as the slower increase of jet temperature, in the case of transcritical injections. The cause for the unique feature is simply explained by the corresponding temperature-density (T-ρ) diagrams. Another unique feature of supercritical jet flows appears in the generation of different flow scales. The power spectrums and the flow fields quantitatively and qualitatively show the different features of flow scales due to the injection conditions. In the transcritical injection, the production of smaller flow scales is considerably enhanced relative to the other injection cases, due to not only its higher density ratio, but also its abrupt variations (leap) of δρ/δT in the T-ρ diagrams. This study indicates, for the present conditions used, that the unique characteristics of supercritical jet flows appear in the mean temperature distributions and the generation of different flow scales, which are simply yet effectively explained by the T-ρ diagrams. © 2011 by the authors.

A front-tracking method with projected interface conditions for compressible multi-fluid flows
TERASHIMA Hiroshi, TRYGGVASON Gretar
微粒化シンポジウム講演論文集 = Symposium (ILASS-Japan) on Atomization, 16 Dec. 2009, Japanese

Transonic aeroelastic computations of a delta wing configuration with high fidelity equations
Hiroshi Terashima, Kenji Ono
Computational Fluid Dynamics 2006 - Proceedings of the Fourth International Conference on Computational Fluid Dynamics, ICCFD 2006, 01 Jan. 2009

Reliability of compressible flow/structure coupling method on Cartesian grid with signed distance field
Hiroshi Terashima, Kenji Ono
2007 Proceedings of the 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007, 01 Dec. 2007
A compressible flow solver coupled with moving/deformed geometries on Cartesian grid with Signed Distance Field (SDF) is developed and its capability is investigated through computations of several basic flow fields for future applications with certain reliability. The flow solver is designed so that SDF includes sufficient geometrical information to compute flow fields. Since information of moving/deformed geometries is recognized as a change of the SDF between time steps, the flow solver can be coupled with moving/deformed geometries naturally. The implementation of this solver is simple and easy. No modification is needed in the main part of the flow solver. Furthermore, the interpolation and the corresponding stencils searching process are not required. Several basic flow fields around fixed/moving cylinders and a fixed sphere are computed in order to validate the proposed solver, in which the computed results are compared with available numerical and experimental results. The results demonstrated the method's capability for moderate Reynolds number flows around both of fixed and moving geometries. Based on the results, some criteria and problems for obtaining reliable solution are suggested. Copyright © 2007 by ASME.

Effects of number of stores on the transonic flutter characteristics of a delta wing configuration
Hiroshi Terashima, Kozo Fujii
34th AIAA Fluid Dynamics Conference and Exhibit, 01 Dec. 2004
Transonic and supersonic flutter characteristics of a delta wing configuration with external stores are simulated using the fluid/structure coupling method and the effect of the store aerodynamics is investigated. A delta wing with one and two external stores are considered in this study. The stores are located in the rearward of the wing simulating typical high speed aircraft configurations. The computational result shows that the flutter dynamic pressures over all the Mach numbers are reduced by adding external stores for both cases. In addition, the flutter dynamic pressures become much lower when the number of attached external stores is increased. In the case of the single external store, influence of the store aerodynamics can be divided into two regions according to the Mach number. It is found that neglecting the store aerodynamics leads to the overestimation of the flutter dynamic pressures in the supersonic region. In case of two external stores, the store aerodynamics influence on the flutter boundary only at M∞ = 1.22 unlike the case of the single external store. It is shown that the shock wave ahead of the external store influences on the pressure distributions on the lower surface and the location of the shock wave is important for the decision of the flutter boundary. © 2004 by the American Institute of Aeronautics and Astronautics, Inc.

Numerical Estimations of Transonic Flutter Phenomena with Fluid/Structure Coupling Method
TERASHIMA Hiroshi, FUJII Kozo
年次大会講演論文集 : JSME annual meeting, 20 Sep. 2002, Japanese
Flutter phenomena for the AGARD445.6 standard aeroelastic wing in the transonic flow are simulated using the fluid/structure coupling method. The effect of time accuracy, number of the inner-iterations and comparison of a fully implicit coupling method with a loosely coupling method are examined. The sufficient number of inner-iterations in time is required for the accurate prediction of time responses when using a large time step. Improvement of the solution time accuracy for the aerodynamic equations is key for accurate aeroelastic computations and the one-step time lag generated in a loosely coupling method does not have an effect in the flutter prediction in transonic flows.

708 Some problems found in the CFD analysis of Space Transportation Systems
FUJII Kozo, MORIYA Koichiro, TERASHIMA Hiroshi, HORIE Toshiyuki
Fluids engineering conference ..., 28 Sep. 2001, Japanese
CFD simulations using three-dimensional compressible Navier-Stokes equations are carried out for the establishment of the reliability of the CFD tools for the aerodynamic evaluation of space transportation systems. Simulations for Apollo-type capsule show that the simulations with typical number of grid points can give us reasonable result and CFD analysis can be a useful tool for the initial estimation of aerodynamic characteristics. Simulations for the FTB configuration show the dependency of the aerodynamic data on the order of accuracy of the simulations. The flow field near the base alters the characteristics. The example for the delta and double-delta wings which may be a candidate for the future TSTO systems shows that the success of the CFD simulations for delta wings does not necessarily justify the CFD results for similar configurations.

Flow characteristics of unsteady three-dimensional type IV shock interference
Satoru Yamamoto, Hiroshi Terashima
Fluids 2000 Conference and Exhibit, 01 Dec. 2000
Unsteady three-dimensional hypersonic shock/shock interference flows measured by Berry and Nowak1 are calculated using the shock-vortex capturing method with and without thermochemical nonequilibrium effect. This method contains the 4th-order compact MUSCL TVD scheme, the maximum 2nd-order LU-SGS scheme, and the AUSM-based scheme. Two typical 3-D flows around the forward swept fin at the angle of 0° and -15° are first calculated without reaction. The flow pattern and the shock heating on the body surface are well compared with the experiments. These 3-D flows specified by a high temperature condition are also calculated for resolving the effect of thermochemical nonequilibrium. The two-temperature model based on the Park model is employed for the chemical reaction model. The calculated results show that the increase of temperature changes the type of shock interference because of decreasing the shock standoff distance and also suggest that the shock heating might be very sensitive to the type of shock interference. Finally, unsteady flow characteristics captured both with and without thermochemical nonequilibrium effect are preliminarily expressed. © 2000 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

超臨界圧燃焼流れ場の高度デジタル予測に資する詳細反応機構-燃焼LES技術の開発
科学研究費助成事業 基盤研究(B)
01 Apr. 2021 - 31 Mar. 2024
寺島 洋史, 河合 宗司
超臨界圧燃焼流れシミュレーション(超臨界燃焼CFD)を実施するため，まず，熱，輸送物性，そして化学反応モデルに非理想性を考慮した流体物性モデルの開発を行った．非理想性を考慮した物性算出プログラムは，世界で標準的に使用される熱・輸送物性ライブラリChemkinと互換性を持つように設計し，任意反応機構を用いた超臨界燃焼CFD解析が可能となっている．特に本研究では，多くの関連研究で無視されてきた化学反応における非理想性を考慮したモデル構築を行った．化学反応における非理想性は，反応前後のギブス自由エネルギー変化をフガシティーで記述し，最終的には平衡定数の算出において考慮される．高圧水素火炎伝播実験と比較を行い，本モデルが実験で観測された質量燃焼速度の圧力負依存性を再現できることを示した．高圧条件においては，質量燃焼速度予測に理想気体モデルとの差が発生するが，この原因をJoule-Thomson(J-T)効果(エンタルピーの圧力依存性)で説明できることを提示した．例えばアルゴンで希釈されていれば，エンタルピーが負の圧力依存性を持つため，非理想モデルは，理想モデルに比べ低い層流燃焼速度および質量燃焼速度を予測する．J-T効果を用いた非理想性効果の議論はこれまでほとんどなく，本成果は，採択が約35%と競争的で知られている国際燃焼シンポジウムの口頭発表に採択されている．化学反応項LESモデル開発については，これまで開発してきた火炎モデル(LTF)をベースとし，火炎伸張を考慮したモデル拡張(LTF-Beta)を実施した．乱流平面火炎干渉場の解析を通して，wrinkled flame領域では，LTF-BetaがLTFに比べ直接数値解析に近い結果を予測できることを示した．異なる燃焼領域への適用や燃焼速度と火炎伸張率の線形モデルに対するさらなる理論考察が必要であり，継続して研究を実施する．
日本学術振興会, 基盤研究(B), 北海道大学, 21H01522

詳細反応機構-超臨界圧燃焼LES解析を可能とする乱流燃焼モデルの開発
科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(A))
2022 - 2024
寺島 洋史
日本学術振興会, 国際共同研究加速基金(国際共同研究強化(A)), 北海道大学, 21KK0250

Challenges for high-fidelity turbulent combustion simulation based on detailed reaction mechanisms
Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
28 Jun. 2019 - 31 Mar. 2022
Kawai Soshi
This study investigated a high-fidelity turbulent combustion LES method based on detailed reaction mechanisms that reproduce turbulent combustion phenomena using coarse grids. To establish the high-fidelity LES method, we first proposed the localized thickened flame (LTF) model that spatially expands the flame thickness while maintaining the accurate laminar burning velocity and auto-ignition without changing the chemical species distributions inside the flame. Then, based on the LTF model, the turbulent combustion LES method that models the fame curvature effects was proposed and validated through the turbulence and flame interaction problem.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), Tohoku University, 19K21927

Modeling for multi-component flows and combustion dynamics under supercritical pressure environments
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
01 Apr. 2017 - 31 Mar. 2020
Terashima Hiroshi
This study has developed a simulation method for combustion and multi-component flow dynamics under supercritical pressures. The method introduced the non-ideal thermodynamic and transport property models to consider peculiar behaviors that appear in supercritical pressures. All the models were fully validated in comparison with experimental or reference data. The flame propagation problems under supercritical pressures demonstrated that the non-ideal effects in the diffusion coefficient are the most influential for the prediction of laminar flame speeds. Regarding thinner flame in higher-pressure conditions, we have developed a new flame model, with which the flame propagation behavior under elevated pressure conditions was successfully captured even on coarser grids. Besides, we constructed a non-ideal fluid library, with which the non-ideal thermodynamic and transport properties are easily obtained in arbitrary simulation programs.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 17K06939

Combustion-reaction database specialized for accidental fire/explosion simulations
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
01 Apr. 2015 - 31 Mar. 2018
Kuwana Kazunori
The objective of this study was to develop a combustion-reaction database specialized for numerical simulations of fire/explosion phenomena. Kinetic parameters of global reaction models were first determined based on the results of experiments and 1-D detailed-reaction simulations. Numerical simulations were then conducted using the obtained global models and other reduced reaction models to compare with the results of experiments or detailed-reaction simulations. A methodology was finally discussed to select the optimal reaction model depending on the local condition.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Yamagata University, 15H02977

Investigation of Effects of Coaxial Injector Shape on Mixing, Diffusion, and Combustion Process of Cryogenic High-Pressure Propellant
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
01 Apr. 2015 - 31 Mar. 2018
Tsuboi Nobuyuki, KOSHI Mitsuo, HAYASHI A. Koichi, TOKUMASU Takashi, TSUDA Shinichi, TERASHIMA Hiroshi, SHIMIZU Taro, ASAHARA Makoto, MORII Youhi, NAGASHIMA Hiroki, MUTO Daiki, OZAWA Kohei
The numerical and experimental studies on the cryogenic flow under the transcritical and supercritical pressures are performed in order to understand the thermodynamic characteristics and fluid dynamics. The coaxial cryogenic nitrogen jet flows under the supercritical pressure are simulated using ILES/RANS hybrid method. The mean inner jet lengths of the present simulations agree well with those of the previous experiments and numerical simulations. As for the multi-species flow simulations, the numerical method using a hybrid method between the energy equation and pressure-evolution-equation, which is able to prevent from pressure oscillations in the flow, is developed. In the experiments, visualization data and temperature profiles in the cryogenic nitrogen channel flow are measured under the subcritical and supercritical pressures.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Kyushu Institute of Technology, 15H04202

Research on dynamic design method for achieving both high efficiency and environmental performance of small energy conversion equipment
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
01 Apr. 2014 - 31 Mar. 2018
Kaneko Shigehiko
Toward utilization of biofuel and realization of eco-mobility, compatibility of the high efficiency of small energy conversion equipment and environmental performance is an essential condition. The problems to be solved in this study are ① a gas turbine for small power generation operated by natural gas, biogas, coal gas, etc. as fuel, ② a reciprocating engine for dual fuel automobiles using both biogas and liquid fuel as fuel, ③ jet fuel and biofuel for small turbojet engines to be used as fuel.
In each problem, barriers for achieving both high efficiency and environmental performance embedded are ① measures against combustion vibration, ② real-time control algorithm with light calculation load, ③ development of noise reduction device released from a nozzle. We proposed a solution to such dynamic problems inherent in corresponding energy converting devices from a new viewpoint involving chemical reactions.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), The University of Tokyo, 26289053

An approach of modifying the governing equations in a physically-consistent manner for modeling of turbulent mixing and combustion
Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
01 Apr. 2015 - 31 Mar. 2017
Kawai Soshi
In this study, an accurate and robust numerical modeling for simulating realistic chemically reacting flow problems using detailed chemical kinetics was studied. Our approach is to couple our idea of modifying the governing equations in a physically-consistent manner and the concept of artificially thickened flame modeling that maintains physical laminar flame speed while artificially thickening flames. Also, by considering the extension of our approach to applying a high-order accurate numerical method, we proposed flux-based high-order accurate Pade-type filters that can satisfy the conservation law of each specie at the order of the machine zero level, something that existing Pade-type filters fail to do.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Tohoku University, 15K14258

An efficient methodology for combustion flow simulations with large detailed chemical kinetics
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
2014 - 2016
Terashima Hiroshi, KOSHI Mitsuo, MORII Youhi
An efficient methodology for simulations of reactive flows (CFD) with large detailed chemical kinetics has been successfully proposed. The present method consists of a fast explicit time integration method for stiff chemical reaction equations and a species bundling technique for efficient calculations of transport properties of mixture. The present method, in particular, the fast explicit time integration method, provides much faster performance with the order of two or three when compared to a conventional approach, enabling an efficient application of large detailed chemical kinetics in CFD simulations. The method has been successfully applied to a wide range of combustion problems such as knocking phenomena of n-heptane (373 chemical species and 1071 reactions) in internal combustion engines, providing the detailed mechanism of strong pressure wave generation and development associated with end-gas autoignition.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), 東京大学, Competitive research funding, 26390128

Scientific Principle on Risk Analysis of Gas Explosions
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
2011 - 2014
DOBASHI Ritsu, TERASHIMA Hiroshi, KUWANA Kazunori, MOGI Toshio, KOSHI Mitsuo
Studies were conducted to promote scientific understanding on occurrence probability (explosion limit) and consequence (consequent damages) of gas explosions. About the explosion limit, it was found that the limit and its dependence on conditions can be appropriately predicted by considering adequate reaction scheme. About the consequence analysis, precious evaluation method of Markstein number, which is important to estimate flame front instability, has been newly developed. Also, it was found a large scale flame is propagating in self-similar manner and its flame area is growing in fractal manner. The mechanism of accelerating development of consequent damages can be understood. These results highly contribute to promote scientific predictions of gas explosion risks.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), The University of Tokyo, Competitive research funding, 23241051

Development of reduction method of detailed chemical kinetics and its application to reactive flow simulation
Grants-in-Aid for Scientific Research(基盤研究(B))
2011 - 2013
Mitsuo KOSHI
Reactive flow analysis for complex system such as automobile engine knocking and vibratory combustion in gas turbine needs fluid dynamic simulation coupled with detailed chemical kinetics. Because of very large numbers of chemical species involved in combustion, such reactive flow analysis is extremely difficult. We successfully developed a new method for the reduction of number of chemical species. In addition, an ultra fast solver of chemical kinetic equations is also developed and implemented into compressible CFD (computer fluid dynamics) code. As a result, reactive flow analysis now become possible for automobile engine knocking.
Ministry of Education, Culture, Sports, Science and Technology, 基盤研究(B), 東京大学->横浜国立大学, Competitive research funding, 23360095

Research of Combustion Dynamics on Cryogenic Flow under Supercritical Pressure
Grants-in-Aid for Scientific Research(基盤研究(B))
2011 - 2013
Nobuyuki TSUBOI, Susum TERAMOTO, Mitsuo KOSHI, Hayashi HAYASHI, Takashi TOKUMASU, Shinichi TSUDA, Kazuya SHIMIZU, Taro SHIMIZU, Hiroumi TANI, Makoto ASAHARA, Youhi MORII
The numerical and experimental studies on the cryogenic flow under the supercritical pressure are performed in order to understand the thermodynamic characteristics and fluid dynamics. The averaged density distributions of the mono-axial nitrogen jet flow under the supercritical pressure using RANS simulations agree well with the experimental data. The preconditioning method including multi-species mass-conservation equations was developed to capture the unsteady feature near the shear layer in the low-speed H2/O2 shear flow. As for LES simulations, the cryogenic nitrogen/nitrogen mixing layers in ideal-gas and transcritical conditions were also simulated. The results show that the effects of the pseudo-critical temperature are small on the turbulent eddy structure. In the experiment for the cryogenic nitrogen jet under the transcritical pressure, the temperature gradient along the symmetric line becomes small near the pseudo-critical temperature.
Ministry of Education, Culture, Sports, Science and Technology, 基盤研究(B), 九州工業大学, Competitive research funding, 23360380

A front-tracking method for fluid interfaces in high-speed compressible flows
Grants-in-Aid for Scientific Research(若手研究(B))
2011 - 2012
Hiroshi TERASHIMA
A front tracking method for compressible multi-fluid flows is presented where marker points are used both for tracking fluid interfaces and also for constructing the Riemann problem on the interfaces. The Riemann problem between two fluid phases (defined in the interface normal direction) is solved using the exact Riemann solver on the maker points. The solutions are projected onto fixed grid points and then extrapolated into the corresponding ghost fluid regions, as in the ghost fluid method. The proposed procedures are designed to be consistent in any dimensions and to be simple to implement. Several multi-fluid problems, including the breakup of a water cylinder induced by the passage of a shock wave, were computed in order to demonstrate the capability of the new method.
Ministry of Education, Culture, Sports, Science and Technology, 若手研究(B), 独立行政法人宇宙航空研究開発機構->東京大学, Principal investigator, Competitive research funding, 23760079

自己接触を伴う薄膜折りたたみ展開構造物のボディダイナミクスシミュレーション
科学研究費補助金(若手研究(B))
2006 - 2008
寺島 洋史
本研究は,AirbagやParachuteといった流体と干渉する薄膜展開構造物のダイナミクスシミュレーションを行う数値手法の開発と設計への応用を目的とする.流体解析には,大変形薄膜物体を容易かつロバストに扱うため直交格子を用い,構造解析には幾何学的非線形性を考慮した有限要素法を採用した.今年度は,直交格子を用いた流体解析手法の開発と,流体と移動剛体が連成した流体剛体連成解析手法を開発し,その信頼性を評価した.本手法は以下の特長を持つ:1)距離関数場(Signed Distance Filed : SDF)を使用2)プログラムの修正は境界条件部分のみで,オリジナルソルバーからの修正が非常に容易3)鏡面境界条件で見られる境界付近の物理量内挿処理とそれに伴う点探索処理が無い4)SDF情報の変化がダイレクトに物体移動の情報を表し,流体構造連成問題を合理的に扱える特に3)は移動変形物体を扱う際に有利な点である.直交格子の解析でしばしば問題となるのが計算結果の信頼性である.信頼性を検証するため,基本的な流れ場(円柱,球,振動円柱)のシミュレーションを行い,実験や他の計算と比較を行った.固定円柱と球の計算結果から,レイノルズ数500までではあるが,他の結果と良い一致を得た.また,格子解像度の影響を調べ,予想される境界層厚さに10点程度の格子点を配置することにより,信頼性ある解が得られることを示した.これは今後の解析における格子解像度選択の指標となる.振動円柱の解析では,SDFの変化をベースとした本手法が移動物体のシミュレーションに対して有効であることを示し,また,固定円柱の流れ場に比べ,力の振幅や位相を正確に求める上で格子解像度が重要であることを明らかにした.また,粗い格子を用いると,力の時間履歴に虚偽振動が発生することがわかった.この原因は今後の課題である.
文部科学省, 若手研究(B), 独立行政法人理化学研究所, Principal investigator, Competitive research funding, 18760068

Bachelor's degree program, School of Engineering

Master's degree program, Graduate School of Engineering

Doctoral (PhD) degree program, Graduate School of Engineering