研究者データベース

大島 伸行(オオシマ ノブユキ)
工学研究院 機械・宇宙航空工学部門 宇宙航空システム
教授

基本情報

所属

  • 工学研究院 機械・宇宙航空工学部門 宇宙航空システム

職名

  • 教授

学位

  • 工学博士(東京大学)

ホームページURL

J-Global ID

研究キーワード

  • 流体工学   

研究分野

  • ものづくり技術(機械・電気電子・化学工学) / 流体工学

職歴

  • 2005年 - 北海道大学大学院工学研究科 教授 教授
  • 2005年 東京大学生産技術研究所 教授
  • 2005年 - Professor
  • 2005年 Professor
  • 2000年 - 2004年 東京大学情報基盤センター 助教授
  • 2000年 - 2004年 Associate Professor
  • 1991年 - 2000年 東京大学生産技術研究所 助教授
  • 1991年 - 2000年 Associate Professor
  • 1989年 - 1991年 東京大学生産技術研究所 講師
  • 1989年 - 1991年 Lecturer

学歴

  •         - 1989年   東京大学   工学系研究科   舶用機械工学
  •         - 1989年   東京大学
  •         - 1984年   東京大学   工学部   機械工学科
  •         - 1984年   東京大学

所属学協会

  • 応用数理学会   伝熱学会   計算工学会   燃焼学会   可視化情報学会   日本流体力学会   日本自動車技術会   日本機械学会   

研究活動情報

論文

  • Yusuke Takahashi, Masahiro Saito, Nobuyuki Oshima, Kazuhiko Yamada
    Acta Astronautica 194 301 - 308 2022年05月
  • Sangwon Kim, Nobuyuki Oshima, Hyun Jin Park, Yuichi Murai
    International Journal of Multiphase Flow 145 2021年12月 [査読有り]
     
    Bubble drag reduction (BDR) is desirable for achieving better propulsion performance in underwater applications. Large-sized bubbles have significant potential for application in BDR, as they provide excellent drag reduction. In this study, we analyzed the drag modulation effects of large-sized bubbles, especially high-Weber number bubbles, on the horizontal turbulent channel flow using direct numerical simulation. The Weber number (We) was varied from 130 to 337 based on the equivalent diameter and bubble velocity. The two-phase model based on the volume-of-fluid approach and IsoAdvector method for sharpening the bubble interface was used. To study the drag modulation mechanism of large-sized bubble, the skin friction profile along the centerline of the bubble and local mean ratio of skin friction were analyzed at different Weber numbers. The bubble length was found to have a significant effect on drag reduction toward the rear region of the bubble. Based on this observation, we analyzed the influence of the bubble regions on drag modulation by confining each region. The numerical results indicated that the skin friction was sensitive to the bubble size and bubble regions, the changes in the skin friction profile, contour, and local averaged values with the variation in the Weber number were analyzed. Considering the relationship between the bubble regions and skin friction, most bubbles exhibited an increase in drag on the liquid film until We = 337. Meanwhile, the area of drag reduction in the secondary flow increased and broadened with an increasing Weber number. Owing to this tendency, the effect of drag reduction is expected from sufficiently larger bubbles around We = 337. These results afford new insights into bubble-induced drag modulation in different regions of horizontal flow, and important parameters of large-sized bubbly flow for the investigation of overall drag reduction performance.
  • Younghwa CHO, Rahul BALE, Makoto TSUBOKURA, Nobuyuki OSHIMA
    Mechanical Engineering Letters 7 21 - 00136 2021年09月 [査読有り]
  • Hideto Takasawa, Yusuke Takahashi, Nobuyuki Oshima, Hisashi Kihara
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 54 22 2021年06月 [査読有り]
     
    The reentry blackout phenomenon, which is the communication cut-off between the re-entry vehicle and ground station, is a crucial problem that needs to be addressed. To improve safety during reentry, a new mitigation method was proposed using the surface catalysis effect. However, this method has not been investigated extensively by experimental methods. In this study, we experimentally demonstrated the mitigation method using a 1 MW arc-heated wind tunnel and numerically clarified the mitigation mechanism. As a demonstration experiment, communication tests were conducted to compare the two cases. In the first case, a ceramic surface was used as a low catalytic wall, whereas in the second case, a copper surface was used as a high catalytic wall in the arc-heated wind tunnel. The experimental results indicated that the blackout occurred when alumina was used as the low catalytic wall. On the other hand, for the high catalytic wall using copper, blackout was avoided. The tests were reproduced in the wind tunnel using a numerical simulation technique. From the simulation results, the mitigation mechanism suggested that: (a) the number of nitrogen and oxygen atoms decreased due to catalysis; (b) forward reactions of electron impact ionization were suppressed due to the decrease in the number of atoms; and (c) the suppression of reactions decreased the number of electrons, thereby mitigating the reentry blackout. In addition, the numerical simulations performed on the reentry plasma around the re-entry capsule suggested that the mitigation mechanisms between the arc-heated wind flow and reentry plasma were similar despite the different airflow conditions.
  • Shun MURAKAMI, Hiroshi TERASHIMA, Nobuyuki OSHIMA
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 19 2 176 - 185 2021年
  • Yusuke Takahashi, Tatsushi Ohashi, Nobuyuki Oshima, Yasunori Nagata, Kazuhiko Yamada
    PHYSICS OF FLUIDS 32 7 2020年07月 [査読有り]
     
    Aerodynamic instability in the attitude of an inflatable re-entry vehicle in the subsonic regime has been observed during suborbital re-entry. This causes significant problems for aerodynamic decelerators using an inflatable aeroshell; thus, mitigating this problem is necessary. In this study, we revealed the instability mechanism using a computational science approach. To reproduce the in-flight oscillation motion in an unsteady turbulent flow field, we adopted a large-eddy simulation approach with a forced-oscillation technique. Computations were performed for two representative cases at transonic and subsonic speeds that were in stable and unstable states, respectively. Pitching moment hysteresis at a cycle in the motion was confirmed for the subsonic case, whereas such hysteresis did not appear for the transonic case. Pressures on the front surface and in the wake of the vehicle were obtained by employing a probe technique in the computations. Pressure phase delays at the surface and in the wake were confirmed as the pitch angle of the vehicle increased (pitch up) and decreased (pitch down), respectively. In particular, we observed that the wake structure formed by a large recirculation behavior significantly affected the pressure phase delay at the rear of the vehicle. The dynamic instability at subsonic speed resulted from flows that could not promptly follow the vehicle motion. Finally, the damping coefficients were evaluated for the design and development of the inflatable vehicle.
  • Yusuke Takahashi, Naoya Enoki, Hideto Takasawa, Nobuyuki Oshima
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 53 23 2020年06月 [査読有り]
     
    Radio frequency (RF) blackout during atmospheric reentry leads to the cutoff of communication with ground stations and/or data-relay satellites. This causes significant problems during reentry, and thus, mitigation methods have been in high demand. In this study, we numerically demonstrate a novel method for mitigating the RF blackout using surface catalysis effects. Plasma flow behavior and electromagnetic wave propagation around a reentry vehicle were investigated in detail. The approach couples computational fluid dynamics and a frequency-dependent finite-difference time-domain method. The computations were performed with a massive parallelization technique using a large computer. The computed results were compared for cases imposing low and full catalysis conditions on a surface boundary. The investigation revealed that the surface catalysis effects reduce the RF blackout. Atomic species, dissociated across a shock wave formed in front of the vehicle, were recombined on the vehicle surface through surface catalysis. These molecules, flowing into a wake region at the vehicle's rear, caused recombinations of electrons, originally generated in the shock layer. Therefore, a decrease in electrons was observed in the wake region and a wake path, which allows the propagation of electromagnetic waves, was formed. This complicated behavior of the molecules and electrons, induced by the surface catalysis, resulted in mitigation of the RF blackout.
  • CHO Younghwa, BALE Rahul, 小田 剛生, 大島 伸行
    年次大会 2020 J05112  一般社団法人 日本機械学会 2020年
  • Sangwon Kim, Nobuyuki Oshima, Sangeui Lee, Gyoungwoo Lee, Kwangcheol Seo
    Journal of Fluid Science and Technology 15 2 2020年 [査読有り]
     
    This work addresses the numerical study of wave-piercing planing hull and related hydrodynamic performance as the appendages. From the half century ago, the interest in high-speed planing crafts has been advanced toward maintaining performance stably. The main reasons to make it hard are instability motion occurring from porpoising and wave condition. Porpoising is mainly due to overlap the heaving and pitching motion with certain period, which is caused by instable pressure distribution and changing longitudinal location of center of gravity. In addition, in wave condition, encountering wave disturbs going into planing mode. This paper presents numerical results of wave-piercing planing hull in porpoising and wave condition. Numerical simulation is conducted via Reynolds Averaged Navier-stokes (RANS) with moving mesh techniques (overset grid), performed at different wave condition. The numerical results reveal motion characteristics overlapping porpoising and wave condition. At first, motions on low wavelength region show resonance on this condition, and some appendages enhance the motion amplitude larger than original values. Finally, this resonance was suppressed by stern appendages. However, momentum generated from stern appendages increases motions in high wavelength region. This effective motion corresponds with vertical accelerations from CG.
  • Sangwon KIM, Nobuyuki OSHIMA, Yuichi MURAI, Hyun Jin PARK
    Journal of Fluid Science and Technology 15 3 1 - 18 2020年 [査読有り]
     
    Air lubrication systems have gained considerable popularity as a promising drag reduction technology in recent years. However, numerical simulations of intermediate-sized bubbles are quite challenging because of the numerical diffusion of the conventional method and the high deformability of the bubbles. This hinders the study of the physical mechanisms involved in a variety of phenomena in such types of bubbles, such as the bubble–liquid interaction effect, high bubble deformation, and flow in the liquid film generated above the bubble. In this study, a solver, viz. interIsoFoam of OpenFOAM, which is directly captured by the improved volume of fluid method, was applied to solve the gas–liquid interface problem. We established the numerical procedure by dividing it into three stages and validating the accuracy of the given solver to minimize numerical errors such as smearing the volume fractions. The numerical results for variables such as the bubble shape, the skin friction of the liquid film, and the instantaneous momentum flux display trends similar to those observed in the experiments. The calculated bubble shows a high skin friction in the secondary flow, which corresponds to the distribution of streamwise vortices in the secondary flow.
  • Yusuke Takahashi, Taiki Koike, Nobuyuki Oshima, Kazuhiko Yamada
    AEROSPACE SCIENCE AND TECHNOLOGY 92 858 - 868 2019年09月 [査読有り]
     
    An inflatable aerodynamic decelerator with a membrane aeroshell is a promising key technology in the reentry, descent, and landing phases of future space transportation. The membrane aeroshell is generally deformed by the in-flight aerodynamic force; however, the effects of the deformation on the aerodynamic heating are unclear. Here, we investigated aerodynamic heating for an inflatable reentry vehicle, Titans, in the hypersonic regime using flow field simulation coupled with structural analysis. Thermochemical nonequilibrium flows around the Titans with a deformed membrane aeroshell were reproduced numerically for an angle of attack (AoA) values between 0 degrees and 40 degrees. The maximum displacements of the membrane aeroshell by deformation at the AoAs of 0 degrees and 40 degrees were 6.7% and 6.6% of the diameter of the Titans, respectively. The difference in heat fluxes between the deformed and rigid shapes was a remarkable 188.8% for a 0 degrees AoA owing to the considerable changes in the front shock wave shape. Meanwhile, it was indicated that membrane deformation at an AoA of 40 degrees insignificantly affected the peak heat flux value on the inflatable torus because the considerable change in the shock wave shape observed for the case of 0 degrees AoA did not occur. It was found that local wrinkles on the membrane aeroshell were formed by deformation, thus causing the heat flux to increase owing to an increase in local temperature gradient on the surface. (C) 2019 Elsevier Masson SAS. All rights reserved.
  • Jiaming Gong, Nobuyuki Oshima, Yutaka Tabe
    Computers and Mathematics with Applications 78 4 1166 - 1181 2019年08月15日 [査読有り]
     
    The spurious velocity resulting from the cutoff and magnification equation in the free-energy-based one-component-two-phase flow lattice Boltzmann method (LBM) for a large density ratio proposed by Inamuro et al. [34] is investigated. In Inamuro's model, the phase interface is tracked by the order parameter, which is the dimensionless density of a two-phase flow system with a small density ratio. The velocity field is calculated based on the density profile of a two-phase system with a large density ratio, which is derived from the order parameter profile through a sine type of cutoff and magnification equation; this velocity field is then used to drive the movement of a phase interface described by the order parameter. The implementation of the cutoff and magnification equation causes the density profiles in the two systems to differ from each other such that force balances across the interfaces break from the ideal state and lead to spurious velocity. Three measures: (1) the linear cutoff and magnification equation which equalizes the density profiles in the interface region, (2) a new scheme which enhances the smoothness of the density profile around the cutoff points in the large density ratio system and (3) a special method that increases the interface thickness of the large density ratio system are adopted to reduce the magnitude of the spurious velocity from the profile difference, respectively. We show that all of these measures can successfully reduce the magnitude of the spurious velocity to some degree; and the scheme that enhances the smoothness of the density profile around the cutoff points reduces the spurious velocity of the original scheme by one order of magnitude.
  • Naoya Enoki, Yusuke Takahashi, Nobuyuki Oshima, Kazuhiko Yamada, Kojiro Suzuki
    AIP Conference Proceedings 2132 2019年08月05日 [査読有り]
     
    An inflatable nano-satellite with thin-membrane aeroshell, "EGG", was deployed from the International Space Station at an altitude of approximately 400â...km, as part of an orbital deployment mission in 2017. After flight on the low Earth orbit (LEO) for 120 days, EGG successfully reentered Earth's atmosphere and burned out according to mission schedule. During the mission period, surface temperatures of the membrane aeroshell of EGG were measured using thermocouples. The measurement data was sent to the ground station using Iridium short burst data communication. There has not been sufficient investigation of the aerodynamic heating environment of such inflatable vehicles. In this paper, the heat flux on membrane aeroshell was revealed, based on the measured temperature data and a heat conduction simulation technique. In addition, heat flux distributions at an altitude of 120â...km were numerically evaluated using the Direct Simulation Monte Carlo (DSMC) method, for cases where the angle of attack was between 0 and 180°. From the reconstructed heat flux history and the DSMC analysis results, it was found that the heat flux on the inflatable torus was higher than that on the membrane aeroshell. Additionally, it was concluded that EGG was in the heating environment of approximately 3-4 kW/m2 at an altitude of 110â...km.
  • Nobuyuki Oshima, Ryosuke Kishine, Takeo Oda
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 2 2019年 [査読有り]
     
    In this research, the LES with the multiple-scalar flamelet approach is performed for an industrial gasturbine combustor, L30A, produced by Kawasaki Heavy Industries, which can appropriately simulate a partial premixed combustion by methane-hydrogen mixed fuel operation. Its instantaneous and time-averaged data by LES result are analyzed for predict NO production in thermal and prompt regime under different operation conditions. PDF statistical analysis is also applied to evaluate the effects from turbulent fluctuations of flame propagation and mixture fraction. These analyses reveal different mechanisms of turbulent fluctuations to increase or decrease NO productions.
  • Shun Murakami, Hiroshi Terashima, Nobuyuki Oshima
    AIAA Scitech 2019 Forum 2019年 [査読有り]
     
    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.
  • Mahiro Ooe, Hiroshi Terashima, Jun Hayashi, Fumiteru Akamatsu, Nobuyuki Oshima
    12th Asia-Pacific Conference on Combustion, ASPACC 2019 2019年 [査読有り]
     
    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.
  • Lu Wang, Nobuyuki Oshima, Sangwon Kim
    PROCEEDINGS OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019, VOL 5 2019年 [査読有り]
     
    A series of numerical simulations using "interThermalPhaseChangeFOAM" solver with improved VOF multiphase flow model in OpenFOAM were conducted to investigate the heat transfer and phase change characteristics for liquid-vapor boiling flow in quenching process. The computational domain is a cuboid with the heating wall at the bottom for both the variable and fixed wall temperature cases. The results for the variable wall temperature case with the heating wall temperature T-wall=150K show that the boiling phenomenon can be divided into the vapor film stage, the boiling stage and the convection stage. Then the fixed wall temperature cases with T-wall=110K, 120K and 140K are analyzed. It is found that 140K case is the most stable one, in which bubble formation is regular such as the bubble at the corner, resulting in the steady variation of heat flux. 120K case is the most unstable one, since the liquid phase and gas phase form the cross-interface shape and maintain this for a long time, leading to the fluctuations in heat flux. Finally, the influence of computational sizes on predicting the properties of boiling phenomenon is investigated. Although the variations of heat flux are not exactly same, the whole tendency is similar.
  • Yusuke Takahashi, Manabu Matsunaga, Nobuyuki Oshima, Kazuhiko Yamada
    Journal of Spacecraft and Rockets 56 2 577 - 585 2019年 [査読有り][通常論文]
  • Hyunjong Kim, Mohan Kumar Dey, Nobuyuki Oshima, Yeon Won Lee
    Computation 6 4 53 - 53 2018年12月01日 [査読有り]
     
    A study on sloshing characteristics in a rectangular tank, which is horizontally excited with a specific range of the Reynolds number, is approached numerically. The nonlinearity of sloshing flow is confirmed by comparing it with the linear solution based on the potential theory, and the time series results of the sloshing pressure are analyzed by Fast Fourier Transform (FFT) algorithm. Then, the pressure fluctuation phenomena are mainly observed and the magnitude of the amplitude spectrum is compared. The results show that, when the impact pressure is generated, large pressure fluctuation in a pressure cycle is observed, and the effects of the frequencies of integral multiples when the fundamental frequency appears dominantly in the sloshing flow.
  • D Deb, MA Uddin, H Terashima, N Oshima
    Journal of Scientific Research 10 2 117 - 131 2018年 [査読有り][通常論文]
  • Taiki Koike, Yusuke Takahashi, Nobuyuki Oshima, Kazuhiko Yamada
    AIAA Atmospheric Flight Mechanics Conference, 2018 209999 2018年 [査読有り]
     
    Aerodynamic heating around a flare-type membrane inflatable vehicle during Earth atmospheric reentry was investigated using numerical simulation approach. This vehicle, which is mainly composed of the capsule, membrane aeroshell and inflatable torus, has been developed by the Membrane Aeroshell for Atmospheric-entry Capsule (MAAC) group as a one of the innovative reentry systems. Analysis solver for reentry flows around the vehicle was RG-FaSTAR, which is a branch version of JAXA fast aerodynamic routine (FaSTAR). In addition, structure analysis solver also was used for membrane deformation in a loosely-coupled manner with the flow field. In the present research, the effects of angle of attack (AoA) and membrane aeroshell deformation on aerodynamic heating were investigated. The numerical results showed that heat flux distribution drastically varies with the increase in AoA because of changes of flow field, and heat flux value at the stagnation point for case of AoA of 40 degree was 3.09 times as high as that for 0 degree. Moreover, the deformed shapes for case of AoA of 0 and 40 degrees were calculated in the way which the pressure distributions obtained using initial (undeformed) shape were given as the aerodynamic force. The difference of heat fluxes between the deformed and initial shapes on the head capsule part was remarkable as 188.8% for case of AoA of 0 degree. On the other hand, it was indicated that membrane deformation for case of AoA of 40 degree insignificantly affects the peak heat flux value on the inflatable torus such as the case of the AoA of 0 degree.
  • Hyunjong Kim, Nanjundan Parthasarathy, Kui Ming Li, Yoon Hwan Choi, Nobuyuki Oshima, Yeon Won Lee
    Proceedings of the International Offshore and Polar Engineering Conference 2018-June 741 - 746 2018年 [査読有り]
     
    In order to design a wave energy generating system of a floating type, a 6- Degrees Of Freedom (DOF) motion technique was applied to Computational Fluid Dynamics (CFD) analysis on this floating body and the behavior is interpreted according to the nature of the incoming waves. In the numerical study, the tuning factor concept is employed, as it explains the relation between the maximum pitch angle and the length of the floating body and wavelength. The relation between tuning factor & pitch period for the generated waves is compared to analyze the effects of wave energy absorption. Linear waves are generated in a tank model using a single floater. In this paper, we focus on wavelength of a floater and 14 cases have been modeled for the same. It was found that the wave energy absorption varies in different parameters of wavelengths and also the different locations of the floating body in a wave affect the wave energy absorption, thus necessitating the importance of the location of a floater in a wave and its effect on wave energy absorption.
  • Ohashi Tatsushi, Takahashi Yusuke, Terashima Hiroshi, Oshima Nobuyuki
    JOURNAL OF FLUID SCIENCE AND TECHNOLOGY 13 3 2018年 [査読有り][通常論文]
     
    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.
  • 高橋裕介, 松永学, 大島伸行, 山田和彦
    日本航空宇宙学会誌(特集) 65 12 370 - 376 2017年12月 [査読有り][通常論文]
  • Yusuke Takahashi, Dongheun Ha, Nobuyuki Oshima, Kazuhiko Yamada, Takashi Abe, Kojiro Suzuki
    JOURNAL OF SPACECRAFT AND ROCKETS 54 5 993 - 1004 2017年09月 [査読有り]
     
    A flight experiment of an inflatable reentry vehicle, equipped with a thin-membrane aeroshell deployed by an inflatable torus structure, was performed using a Japan Aerospace Exploration Agency S-310-41 sounding rocket. The drag coefficient history was evaluated by analyzing the acceleration of the vehicle with the atmospheric density and temperature using a global reference atmospheric model. The vehicle successfully demonstrated deceleration. During the reentry flight, the position, velocity, and acceleration of the vehicle were obtained by using the Global Positioning System. The experimental drag coefficient had an almost constant value of 1.5 in the supersonic region but decreased to 1.0 in the subsonic region. In the transonic region, a steep decrease of the drag coefficient was confirmed. To study the detailed aerodynamics for the reentry vehicle, flowfield simulations were conducted with computational fluid dynamics techniques. The aerodynamic force acting on the vehicle was investigated with the measured data throughout the supersonic and subsonic regions. In the flowfield simulation, the computed result for the drag coefficient showed reasonable agreement with the experimental one. In addition, a compressible effect in front of the vehicle was seen to appear in the supersonic region and a vortex ring at the rear of the vehicle was formed in the subsonic region.
  • Jiaming Gong, Nobuyuki Oshima
    Physics of Fluids 29 6 2017年06月01日 [査読有り]
     
    The effect of initial densities in a free energy based two-phase-flow lattice Boltzmann method for non-ideal fluids with a curved interface was investigated in the present work. To investigate this effect, the initial densities in the liquid and gas phases coming from the saturation points and the equilibrium state were adopted in the simulation of a static droplet in an open and a closed system. For the purpose of simplicity and easier comparison, the closed system is fabricated by the implementation of the periodic boundary condition at the inlet and outlet of a gas channel, and the open system is fabricated by the implementation of a constant flux boundary condition at the inlet and a free-out boundary condition at the outlet of the same gas channel. By comparing the simulation results from the two types of initial densities in the open and closed systems, it is proven that the commonly used saturation initial densities setting is the reason for droplet mass and volume variation which occurred in the simulation, particularly in the open system with a constant flux boundary condition. Such problems are believed to come from the curvature effect of the surface tension and can be greatly reduced by adopting the initial densities in the two phases from equilibrium state.
  • Keisuke Tanaka, Tomonari Sato, Nobuyuki Oshima, Jiun Kim, Yusuke Takahashi, Yasunori Lwai
    PROCEEDINGS OF THE ASME POWER CONFERENCE JOINT WITH ICOPE-17, 2017, VOL 1 2017年 [査読有り][通常論文]
     
    Turbulent combustion flows in the partially premixed combustion field of a dry low-emission gas-turbine combustor were investigated numerically by large-eddy simulation with a 2-scalar flamelet model. Partially premixed combustion was modelled with 2-scalar coupling based on the conservative function of the mixture fraction and the level set function of the premixed flame surface; the governing equations were then used to calculate the gas temperature in the combustion field with flamelet data. A new combustion model was introduced by defining a nondimensional equilibrium temperature to permit the calculation of-adiabatic flame temperatures in the combustion field. Furthermore, a conventional G-equation was modified to include spatial gradient terms for the adiabatic flame temperature to facilitate smooth propagation of a burnt state region in a predominantly diffusion flame. The effect of flame curvature was adjusted by means of an arbitrary parameter in the equation. The simulation results were compared with those from an experiment and a conventional model. Qualitative comparisons of the instantaneous flame properties showed a dramatic improvement in the new combustion model. Moreover, the experimental outlet temperature agreed well with that predicted by the new model. The model can therefore reproduce the propagation of a predominantly diffusion flame in partially premixed combustion.
  • Yusuke Takahashi, Reo Nakasato, Nobuyuki Oshima
    AEROSPACE 3 1 2016年03月 [査読有り]
     
    A numerical analysis of electromagnetic waves around the atmospheric reentry demonstrator (ARD) of the European Space Agency (ESA) in an atmospheric reentry mission was conducted. During the ARD mission, which involves a 70% scaled-down configuration capsule of the Apollo command module, radio frequency blackout and strong plasma attenuation of radio waves in communications with data relay satellites and air planes were observed. The electromagnetic interference was caused by highly dense plasma derived from a strong shock wave generated in front of the capsule because of orbital speed during reentry. In this study, the physical properties of the plasma flow in the shock layer and wake region of the ESA ARD were obtained using a computational fluid dynamics technique. Then, electromagnetic waves were expressed using a frequency-dependent finite-difference time-domain method using the plasma properties. The analysis model was validated based on experimental flight data. A comparison of the measured and predicted results showed good agreement. The distribution of charged particles around the ESA ARD and the complicated behavior of electromagnetic waves, with attenuation and reflection, are clarified in detail. It is suggested that the analysis model could be an effective tool for investigating radio frequency blackout and plasma attenuation in radio wave communication.
  • 脇田督司
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 14 ists30 67 - 72 一般社団法人 日本航空宇宙学会 2016年 [査読有り][通常論文]
     

    The purpose of this study is to develop a computational method to predict fuel regressions for hybrid rocket solid fuels. The shape of the flow field changes depending on the regression and vaporization of the solid fuel. This shape change and the heat flux from the combustion gas to the fuel are mutually dependent. Therefore a computational method that can accurately predicts both of the fuel regression and the heat flux is necessary to clarify the mutual dependence of them. In this study, we have developed a computational method to predict the regression phenomenon including the effect of the shape change of the flow field. The developed code predicts the regression phenomena by repeating gas-phase calculations and regression-phase calculations. The wall consisting of grids permits the flow field to be an arbitrary shape. As the first step, the complex chemical reaction was not included and numerical results were compared with a sublimation phenomenon of naphthalene in a non-combustion flow. Numerical results successfully predicted Nusselt number change due to regression qualitatively.

  • Jia-ming Gong, Nobuyuki Oshima, Yutaka Tabe
    PROCEEDINGS OF THE ASME 13TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, 2015 2015年 [査読有り][通常論文]
     
    The free energy based lattice Boltzmann method (LBM) for two-phase flow with large density ratio is used to simulate droplet dynamics in the polymer electrolyte fuel cell (PEFC). The shape deformation of a static water droplet in the gas channel occurred in the simulations was eliminated. In this LBM model, two types of staggered grids which respectively make use of the velocity components from the orthogonal and diagonal directions are blended to calculate the hydrodynamic pressure from the Poisson equation, with the successive over relaxation method (SOR). It is found that the simulated water droplet shape is determined by both the blending factor of the two types of staggered grids and the radius length. The appropriate blending factor for each radius length is summarized to optimize the simulation. The dependence of shape deformation on the blending factor and the radius length is further validated while considering the wettability effect of the solid wall of the gas channel. It is proved that the summarized appropriate blending factors are still practical when the concept of equivalent radius length is adopted.
  • Jia-ming Gong, Nobuyuki Oshima, Yutaka Tabe
    JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 10 1 2015年 [査読有り][通常論文]
     
    The spurious velocity around curved interface, arising from the calculation of the Poisson equation with staggered grids, is reduced in the free-energy-based two-phase flow lattice Boltzmann method (LBM) for large density ratios. It is found that the pressure calculation from the Poisson equation, using the successive over-relaxation method with staggered grids, would introduce anisotropic discretization errors and lead to deviations of its calculated value from the theoretical prediction. Moreover, the anisotropic pressure would induce a large magnitude of spurious velocity, which is the driving force for droplet shape deformation. By blending the velocity components in the discretization equations of the Poission equation from two types of staggered grids that separately make use of the velocity components in the orthogonal and the diagonal directions, the magnitude of the spurious velocity and the droplet deformation are diminshed. It is found that, by appropriate choice of the blending factor, the magnitude of the spurious velocity can be reduced to half of its original value, and the shape deformation and pressure deviation from the theoretical prediction can be minimized.
  • LIU Yingjie, OSHIMA Nobuyuki
    Journal of Thermal Science and Technology 9 1 JTST0002 - JTST0002 The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan 2014年 
    The flamelet model based on the concept of local flame speed S*is newly developed to describe a premixed flame with a finite thickness when defining G as the non-dimensional temperature. In the previous work the new flamelet model was validated by 1-D steady premixed flame successfully. In this paper the model of 3-D counter flow premixed methane-air is investigated. The local flame speed can be proposed as S*=Su+2Su(G-G0) where the scalar G=G0 represents the flame surface in the flamelet model. Considering the stretch effect the expression for the modified burning velocity is Su=Su0-Su0 where Su is smaller than the burning velocity of the unstretched flame Su0. The new flamelet model results are compared with the original G-model results in the velocity and the temperature profiles. The results are also validated by the detailed chemical reaction solution of GRI-Mech3.0 by CHEMKIN.
  • Yusuke Takahashi, Nobuyuki Oshima, Yasunori Iwai
    11TH WORLD CONGRESS ON COMPUTATIONAL MECHANICS; 5TH EUROPEAN CONFERENCE ON COMPUTATIONAL MECHANICS; 6TH EUROPEAN CONFERENCE ON COMPUTATIONAL FLUID DYNAMICS, VOLS V - VI 5792 - 5803 2014年 [査読有り]
     
    Combustion flow field in an industrial gas-turbine combustor was numerically investigated with a newly-developed turbulent combustion model. For turbulent model, large-eddy simulation technique was introduced to simulate unsteady phenomena in detail. The combustion model was based on a two-scalar flamelet approach coupling the two concepts of premixed and non-premixed flames expressed by the conservative scalar of mixture fraction and the levelset function of premixed flame surface, respectively. A fine full tetra computational mesh of 45.5 million cells and 7.7 million nodes was used to resolve turbulent fluctuation with high accuracy in the combustion field. The simulations were performed for two calculation conditions reproducing diffusion-like and premixed-like flames and for three conditions decreasing fuel inlet to investigate flame extinction behavior. It was indicated that premixed or partial premixed turbulent flames by complex burner system in the real scale combustor can be reasonably captured by the present simulation model.
  • 岡崎 輝幸, 柴田 強, 小林 啓信, 池内 壽昭, 大島 伸行
    日本機械学会論文集 B編 79 803 1375 - 1390 The Japan Society of Mechanical Engineers 2013年 
    The melting furnace of a municipal solid waste gasification and melting system must have a high slag recovery rate and low dioxin emission. In this study, we developed a vertical swirling melting furnace with multistage air nozzles which can be used in the gasification and melting system. Three stage nozzles for feeding air and fuel are installed on a cylindrical furnace. Each nozzle is arranged in a tangential direction to generate swirling flow. The fuel is supplied by the primary nozzle which is located at the lowest level among the nozzles. Combustion air is supplied by the secondary and tertiary stage nozzles. The flow pattern of this furnace is similar to that of a cyclone separator. Most of the fuel goes down to the bottom of the furnace and burns in the swirl flow. The furnace design was done using a one-dimensional heat balance simulation tool. In this simulation, distribution of air mass flow in the furnace was determined by an air flow model experiment. The simulation results were compared with measured data from a 20t/day demonstration plant, and accuracy of the developed design tool was verified. The temperature prediction error was less than 40 degC. In the demonstration plant, the slag recovery rate of the melting furnace was higher than 90%, and the dioxin concentration in the flue gas at the chimney was lower than the government regulation value.
  • K. M. Salahuddin, Akira Nishimura, Nobuyuki Oshima, Litan Kumar Saha
    JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 8 1 209 - 224 2013年 [査読有り]
     
    The three-dimensional, transient, isothermal, gas-flow behavior in the serpentine channel and porous gas-diffusion layer (GDL) of a polymer electrolyte membrane fuel cell was investigated numerically. Decreasing the pitch length of the channel increases the pressure drop. In the serpentine channel, reactant gas is distributed from one part of the channel to another through the GDL by cross flow induced by a pressure differential between adjacent channels. The amount of cross-flow, quantified in terms of the volume mass flux through the GDL under the rib and between two channels, is controlled predominantly by the thickness of the GDL, the pitch length of the channel, and the permeability. The permeability of the GDL has marked effects on the pressure drop and on cross flow. The cross flow rate through the GDL increases when decreasing the pitch length of a serpentine channel. Cross flow reduces the pressure gradient in the channel, whereas bends improve the pressure gradient. The pressure gradient in the channel increased with decreasing cross flow.
  • K. M. Salahuddin, Nobuyuki Oshima, Litan Kumar Saha
    PROCEEDINGS OF THE 11TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, 2013 2013年 [査読有り]
     
    In this article we presented the recent activities in the field of gas flow in the micro channel and porous media of a polymer electrolyte fuel cell (PEFC). The gas flow behavior in the micro-channel, especially in the case of serpentine channel is very complex due to the appearance of cross flow through the gas diffusion layer (GDL). The gas flow behavior in the separator channel and GDL of a PEFC has been studied by using a transient, isothermal and three dimensional numerical models. To predict gas flow phenomena accurately the precise calculation of mass conversation is necessary which is strictly maintained in our present simulation. The effects of physical characteristics and geometrical properties have been investigated to quantify the amount of cross flow and pressure loss. The cross flow has been investigated in terms of volume mass flux through the GDL under the rib. The ratio cross flow rate to the total flow rate increases when gas channel pitch length decreased. Moreover, with increasing of permeability this ratio also increases. The effect of cross flow and bend region characteristics on the pressure loss has been identified. In addition, to isolate the contribution of cross flow on the performance of fuel cell, the simulation was carried out with electrochemical reaction using parallel straight channel. We designed a parallel flow field to induce artificial cross flow through the GDL. The numerical results show that the flow cross-over through the GDL under the rib significantly facilitate the oxygen transport towards the catalyst layer. Therefore, it is possible to overcome the oxygen transport limitation. Consequently, the cross flow can increase the current density by reducing the oxygen transport limitation, although this also increases the non-uniformity in current density.
  • Jia-ming Gong, Nobuyuki Oshima, Yutaka Tabe
    PROCEEDINGS OF THE 11TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, 2013 2013年 [査読有り][通常論文]
     
    The effect of blend proportional factor a used in the free energy based two-phase flow LBM model with large density ratio on the shape description of a water droplet is investigated. The blend proportional factor a which combines the two kinds of staggered grids is adopted in the calculation process of the Poisson equation based fractional step method to satisfy the mass conservation in the LBM scheme, it is found to lead to varied degrees of shape deformation of a simulated liquid water droplet. The shape deformation degree of a liquid water droplet with certain dimensionless radius is measured by the radius lengths in 8 directions. The appropriate a which gives the better shape description accuracy of a water droplet with certain dimensionless radius is explored and its value change tendency with the dimensionless radius lengths is summarized The a's effect on the shape deformation is also presented
  • Molecular Dynamics Study of Nano-scale Liquid-gas Interface Inspired by Fuel Cell Catalyst Layer
    Youngmin Kim, Hisao Yaguchi, Nobuyuki Oshima, Masao Watanabe, Kazumichi Kobayashi
    ASME 2013 11th International Conference on Nanochannels 2013年 [査読有り][通常論文]
  • MUTO Masaya, TSUBOKURA Makoto, OSHIMA Nobuyuki
    J Vis 15 3 261 - 268 2012年08月 [査読有り][通常論文]
  • Litan Kumar Saha, Nobuyuki Oshima
    JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY 26 5 1315 - 1320 2012年05月 
    A serpentine flow channel is one of the most common and practical channel layouts for Polymer electrolyte fuel cells (PEFCs) since it ensures the removal of water produced in the cell with an acceptable parasitic load. The operating parameters such as temperature, pressure and flow distribution in the flow channel and gas diffusion layer (GDL) has a great influence on the performance of PEFCs. It is desired to have an optimum pressure drop because a certain pressure drop helps to remove excess liquid water from the fuel cell, too much of pressure drop would increase parasitic power needed for the pumping air through the fuel cell. In order to accurately estimate the pressure drop precise calculation of mass conservation is necessary. Flow crossover in the serpentine channel and GDL of PEFC has been investigated by using a transient, non-isothermal and three-dimensional numerical model. Considerable amount of cross flow through GDL is found and its influence on the pressure variation in the channel is identified. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.
  • Litan Kumar Saha, Yutaka Tabe, Nobuyuki Oshima
    JOURNAL OF POWER SOURCES 202 100 - 107 2012年03月 [査読有り][通常論文]
     
    In this study the deformation effect of a gas diffusion layer (GDL) on the pressure drop of a polymer electrolyte fuel cell (PEFC) separator channel has been investigated both numerically and experimentally. Pressure drop is considered as a diagnostic tool to monitor the performance of a PEFC. The deformation of the GDL caused by the compression pressure plays an important role in the performance of a PEFC since it affects the physical properties of the GDL, such as porosity, permeability and the cross sectional area of the gas channel. The flow behavior in the separator channel and GDL of PEFCs has been investigated by using a transient, isothermal and three-dimensional numerical model. To develop the numerical simulation of PEFC, verification experiments and data acquisition of physical parameters were conducted by mechanical measurements. The experimental results showed that estimating the actual flow configuration in the cell, the GDL deformation shape due to clamping by the separator lands has a significant influence. The numerical result shows that together with the deformation shape, the GDL physical parameter variation also needs to be considered in order to predict the actual flow phenomena. Moreover, the results can estimate the physical parameters under deformed condition qualitatively. (C) 2011 Elsevier B.V. All rights reserved.
  • 岡崎輝幸, 鈴木朋子, 山本研二, 仲田博幸, 藤田修, 大島伸行
    日本機械学会論文集 78 786 132 - 146 The Japan Society of Mechanical Engineers 2012年02月 [査読有り][通常論文]
     
    A computational model was developed to predict the pyrolysis process of municipal solid waste in externally heated rotary kiln. The model was calculated assuming solid waste and gas are one-dimensional flow. The heat transfer coefficient among solid waste, gas and inner cylinder of kiln, which is variously affected by kiln structure and operation condition, was acquired by a scale model examination. A flexible computational grid was adopted in the model, which could change its shape according to the height of solid waste layer in each time step. The accuracy of this model was verified by comparison with the pilot scale experiments and the actual plant data. The predicted transient temperature profile is in good agreement with experimental data. Compared to the actual plant data, temperature prediction error is less than 10% at inner cylinder wall, pyrolysis gas, and solid waste.
  • Jia-ming Gong, Nobuyuki Oshima, Eru Kurihara, Yutaka Tabe
    PROCEEDINGS IF THE ASME 9TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS AND MINICHANNELS 2011, VOL 1 239 - 248 2012年 [査読有り][通常論文]
     
    The appropriate blend proportional factor value which combines two kinds of staggered grids used in Lattice Boltzmann Method (LBM) for simulating the multiphase flow phenomena with large density ratio in the Polymer electrolyte fuel cell (PEFC) is fixed on. The shape deformation of the water droplet is found when using the two kinds of staggered grids to prevent the pressure oscillation when solving the Poisson equation of this LBM model and the shape of the water droplet varies with the changes of the blend proportional factor values. Two methods are adopted to find out the two staggered grids' appropriate blend proportional factor value that can diminish or minimize the deformation of the droplet. The first one is to compare the simulation results of different blend proportional factors with the theoretical value and find the one mostly approaches the theoretical value; the second one is to compare the current velocity divergences of the two staggered grids using the results calculated by different blend proportional factor values. A water droplet resting in a tunnel is simulated with different blend proportional factor values and the appropriate value is decided.
  • Akter Hossain, Nobuyuki Oshima, Yuji Nakamura, Marie Oshima
    COMBUSTION THEORY AND MODELLING 16 5 799 - 816 2012年 [査読有り][通常論文]
     
    In this study, the influence of the negative velocity field formed ahead of an abruptly deformed flame tip on the propagation behaviour of a laminar premixed flame is numerically investigated. A strong deformation in the flame front is induced by imposing a very narrow, in-line pre-heating zone in the unburned region. The simulation is performed under low Mach number approximation by using a multi-scale multi-physics Computational Fluid Dynamics (CFD) solver FrontFlow/Red with one-step finite rate chemistry in order to track the time-dependent flame dynamics. The computed results unveil that the flame front is deformed significantly within a short time due to the narrow in-line pre-heating effect. The flame deformation induces a strong negative velocity field ahead of the deformed flame tip, acting in the direction of propagation, which gives rise to a strong pair vortex. This strong pair vortex interacts with the flame tip and then slides down along the flame surface in the upstream direction during propagation. This flame-vortex interaction causes further deformation in the flame surface in the upstream direction, and consequently, the flame exhibits a wave-like surface, which enhances the flame propagation speed. The auto-generation of a strong pair vortex ahead of the flame front due to the localised thermal input could be applied as one of the methods to control the combustion externally. It is also expected that the results obtained in this study could have a significant impact on the detailed understanding of the local thermo-fluid dynamical interaction process of turbulent combustion in practical combustors.
  • MUTO Masaya, TSUBOKURA Makoto, OSHIMA Nobuyuki
    Phys Fluids 24 1 14102  2012年01月 [査読有り][通常論文]
     
    Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 × 104, 2.0 × 1051.14 × 106. The numerical methods used were first validated on a non-rotating spherethe spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachmentturbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point. © 2012 American Institute of Physics.
  • LIU Yingjie, OSHIMA Nobuyuki
    Journal of Thermal Science and Technology 6 1 140 - 153 The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan 2011年 
    In this paper we propose a new level set approach to describe not only a flame's surface but also to the flame's spatial distribution. First, we derived the mathematical formulation for a one-dimensional laminar premixed flame, where the steady flame has a finite thickness depending on the diffusion flux whose physical quantity such as temperature has a relation to index function G . Further, to investigate the relationship between the present model and Inage's model, we extracted the physical meaning from the energy equation. We also validated another important parameter, the heat reaction release rate using the modified G-equation. The analysis of the heat release term leads to the definition of local flame speed, describing the distribution in the flame thickness. We evaluated the distribution of local flame speed with scalar G based on the one-dimensional solutions of premixed flames obtained by the detailed chemical reaction GRI-Mech3.0 using CHEMKIN. For CH4/Air premixed fuel, we carried out a series of calculations with different fuel rates and inlet temperatures. Based on the linear distribution of local flame speed, the modified G-equation can again be certified as the hyperbolic tangent profile.
  • Juanfang Liu, Nobuyuki Oshima, Eru Kurihara
    HEAT TRANSFER ENGINEERING 32 7-8 609 - 615 2011年 [査読有り][通常論文]
     
    A one-dimensional two-phase steady model is developed to analyze the coupled phenomena of cathode flooding and mass-transport limitation for a polymer electrolyte fuel cell. In the model, the liquid water transport in the porous electrode is driven by the capillary force based on Darcy's law, while the gas transport is driven by the concentration gradient based on Fick's law. Furthermore, the catalyst layer is treated as a separate computational domain. The capillary pressure continuity is imposed on the interface between the catalyst layer and the gas diffusion layer. Additionally, through Tafel kinetics, the mass transport and the electrochemical reaction are coupled together. The saturation jump at the interface between the gas diffusion layer and the catalyst layer is captured in the results. Meanwhile, the results further indicate that the flooding situation in the catalyst layer is much more serious than that in the gas diffusion layer. Moreover, the saturation level inside the cathode is largely related to the physical, material, and operating parameters. In order to effectively prevent flooding, one should first remove the liquid water residing inside the catalyst layer and keep the boundary value of the liquid water saturation as low as possible.
  • 武藤 昌也, 坪倉 誠, 大島 伸行
    日本機械学会論文集B編 77 775 781 - 792 日本機械学会 2011年 [査読有り][通常論文]
     
    Flow characteristics and fluid force on a sphere rotating along with axis perpendicular to mean air flow were investigated using Large Eddy Simulation (LES) at two different Reynolds numbers Re_[p] of 1.0×10^[4] and 2.0×10^[5]. As a result of simulation, opposite flow characteristics around the sphere and displacement of the separation point were visualized depending on the Reynolds number even though rotation speed according to the Reynolds number is the same. When the sphere rotates at some specific rotation velocity and at Re_[p] = 1.0×10^[4], flow characteristics agree with the flow fie...
  • Yudai Kaneko, Kouichi Kishida, Nobuyuki Oshima, Takuji Nakashima, Masashi Wakita, Tsuyoshi Totani, Harunori Nagata
    Journal of Space Engineering 3 1 52 - 65 The Japan Society of Mechanical Engineers 2010年11月 [査読有り][通常論文]
     
    In order to clarify the temporal variations of internal ballistics during firing in a cascaded multistage impinging-jet (CAMUI)-type fuel grain, observations of instantaneous flow fields by numerical analysis along with instantaneous grain geometries were conducted. Two static firing tests were conducted under the same conditions, with the exception of firing duration, to obtain the temporal shapes of fuel grains and the characteristics of the regression progress. Two numerical analyses were conducted using the initial and instantaneous geometries to observe internal flow fields. A pair of vortices that is formed near the circumference of the grain due to the change in direction of the flow from the wall jet to the port flow induces a fan-like regression distribution. Two wall jets collide with each other at the center of the grain, roll up and form a fountain-like flow and a pair of gap-scale vortices. These vortices cause an unequal regression distribution on the end faces. On the downstream-end face, the vortices enhance the local regression rate near the axis of the grain. On the forward-end face, in addition to the region near the axis of the grain, the local regression rate at the reattachment points of the vortices increases. These gap-scale vortices disappear as regression progresses because of the dilation of the clearance between the fuel blocks. As a result, the regression rate distributions on both end faces become nearly flat with the progress of fuel regression.
  • 岸田 耕一, 金子 雄大, 大島 伸行, 永田 晴紀
    日本機械学會論文集. B編 76 765 789 - 794 一般社団法人日本機械学会 2010年05月 [査読有り][通常論文]
     
    This paper investigates a thermal-fluid dynamics of CAMUI (Cascaded Multistage Impinging-jet) type hybrid rocket developed in Hokkaido University by using a large eddy simulation of turbulence. The performance of the hybrid rocket is sensitive to the changing shape of its chamber. To clarify this effects, numerical simulations were conducted using measured shapes. The results show the flow structures such as impinging fountain flow depending on the shapes at different burning time. Thease structures generate the particular heat flux distributions on the surface.
  • 武藤昌也, 坪倉誠, 大島まり, 大島伸行
    日本機械学会論文集 B編 76 764 563 - 569 2010年04月 [査読有り][通常論文]
     
    Flow aspects near a particle are observed using a numerical simulation of periodically rotating spherical particle in a uniform flow or static particle in a periodically oscillating flow, to investigate a modulation of drag force. As a result, a reduction of drag force is found and it depends on period and amplitude of the rotation or the oscillation. A reason of the reduction of drag force is caused by a reduction of friction force on the particle. And the reduction of the friction force is induced by a concentration of the fluctuation energy of the flow by the rotation or the oscillation on the vicinity of the particle in case Stokes layer thickness, which is estimated using a frequency of the rotation or the oscillation, is comparable or smaller than the thickness of boundary layer of the particle that is estimated in a laminar flow.
  • シャハ リタンクマー, 大島 伸行, 田部 豊, 栗原 央流
    年次大会講演論文集 2010 197 - 198 一般社団法人日本機械学会 2010年 
    In this study, the deformation effect of gas diffusion layer (GDL) on the pressure drop of polymer electrolyte fuel cell (PEFC) separator channel has been investigated both numerically and experimentally. Gas channel and gas diffusion layers are regarded as two important parts of PEFC because they transport reactant gases to the catalyst layer and also byproduct from the catalyst layer. The deformation of GDL caused by the compression pressure plays an important role in the performance of PEFC since it affects the physical properties of the GDL, such as porosity, permeability and the cross sectional area of the gas channel. The flow behavior in the separator channel and GDL of PEFC has been investigated by using a transient, isothermal and three-dimensional numerical model. To develop the numerical simulation of PEFC, verification experiments and data acquisition of physical parameters were conducted by mechanical measurements.
  • SAHA Litan Kumar, KURIHARA Eru, OSHIMA Nobuyuki
    Journal of Fluid Science and Technology 5 2 259 - 269 The Japan Society of Mechanical Engineers 2010年 
    A numerical comparison of time-stepping schemes for the solution of the conservation equations of mass and momentum of polymer electrolyte fuel cells (PEFCs) is presented. Darcy drag force is the dominating term for the fluid flow inside the gas diffusion layer (GDL). Permeability of the GDL is usually very small. Convergence of continuity is a major problem for the fluid flow through the GDL, and the situation becomes critical in lower-permeability cases. To overcome this kind of severe situation, an implicit scheme is used to obtain not only faster convergence but also a more accurate continuity condition. Explicit, implicit and semi-implicit treatment of the Darcy drag term is considered, and the schemes are compared for various physical parameters of the GDL, e.g., the Darcy number and the porosity parameter, by one dimensional numerical simulation. Influence of strict convergence on the secondary flow effect and on the pressure loss is described and the superiority of implicit scheme is confirmed for three-dimensional numerical simulation of PEFC channel flow.
  • Makoto Tsubokura, Takuji Nakashima, Kozo Kitoh, Yoshihiro Sasaki, Nobuyuki Oshima, Toshio Kobayashi
    SAE International Journal of Passenger Cars - Mechanical Systems 2 1 168 - 178 2009年 [査読有り][通常論文]
     
    A numerical method specially designed to predict unsteady aerodynamics of road vehicle was developed based on unstructured Large-Eddy Simulation (LES) technique. The code was intensively optimized for the Earth Simulator in Japan to deal with the excessive computational resources required for LES, and could treat numerical meshes of up to around 120 million elements. Moving boundary methods such as the Arbitrary Lagrangian-Eulerian (ALE) or the sliding method were implemented to handle dynamic motion of a vehicle body during aerodynamic assessment. The method can also model a gusty crosswind condition. The method was applied to three cases in which unsteady aerodynamics are expected to be crucial. © 2009 SAE International.
  • ITOH Yuichi, OSHIMA Nobuyuki
    Journal of Thermal Science and Technology 4 1 122 - 130 The Japan Society of Mechanical Engineers and The Heat Transfer Society of Japan 2009年 
    In the present study, Large-Eddy Simulation (LES) modeling for turbulent spray combustion flows has been developed in conjunction with the Eulerian/Lagrangian method for the gas phase and dispersed phase representation and flamelet approach for combustion modeling. Moreover, a new thermal energy coupling model is proposed to estimate the thermal interaction between the gas phase and the dispersed phase. The governing equations for the gas phase are the mass and momentum conservation equations and the mixture fraction transport equation. The governing equations for spray droplets are the mass, momentum, and thermal energy equations for each droplet. We applied the numerical procedure to a laboratory-sized spray combustor and found that procedure can predict key features of turbulent spray combustion phenomena, such as the temperature distribution of the combustion gas, individual droplet behavior, and droplet vaporization phenomena. Moreover, the flame temperature drop caused by the thermal impact from the spray droplets is expressed properly by employing the coupling model.
  • シャハ リタン クマ, 栗原 央流, 大島 伸行
    年次大会講演論文集 2009 137 - 138 一般社団法人日本機械学会 2009年 
    Solid matrix drag term usually results in a significant pressure drop across the porous medium. The general momentum conservation equation reduces to the extended Darcy's law for the flow in porous media. So Darcy resistance force is very important for the numerical simulation inside the porous media. A new implicit fractional step algorithm is used for the numerical treatment of Darcy drag term and its effect on the residual error of continuity is studied in the present investigation. Faster convergence and reduced mass conservation error is found by using this algorithm.
  • Masaya Muto, Marie Oshima, Nobuyuki Oshima
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 75 1 61 - 67 2009年01月 
    A descending rate of falling particles through a quiescent or a turbulent airflow, in which the turbulent level is kept constant by rotating grids as a turbulent generator, has been investigated considering particle volume fraction and Stokes number as experimental conditions. In the experiment, turbulent flow properties and downward flow induced by particles are measured by means of LDV. Particles velocity is measured by means of 2 D PTV with laser sheet and CMOS camera. As a consequence, in the quiescent flow a descending rate is reduced for the particles with diameter 0.5 mm and volume fraction of 10 , and further reduction is expected by increasing volume fraction. While, the effect of volume fraction range is expected to be different depending on the diameter. On the other hand, in the turbulent flow (St'-10 ), the descending rate is increased but its mechanism is not explained by existing studies. In the case of solid air two phase flow, the motion of particles are governed by drag and gravity so that a discrepancy of descending rate between present experiment and prediction by existing equation indicates a change of drag under present experimental conditions. 4 3
  • Akter Hossain, Nobuyuki Oshima, Yuji Nakamura, Marie Oshima
    JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 4 2 214 - 225 2009年 [査読有り][通常論文]
     
    In this paper, the effect of ignition area on the propagation of a laminar premixed flame is investigated numerically in a two-dimensional channel. A single-step irreversible overall exothermic chemical reaction is applied to model combustion chemistry. The time-dependent system of governing equations for reacting flows is discretized using the finite volume method (FVM) on the hexahedral structure grid cells. The discretized system of equations is solved by adopting Front Flow Red, a multi- scale and -physics computational fluid dynamics (CFD) solver. The computed results show that the flame oscillates during the propagation owing to the strong roll-up of the vortices generated by the strong shear layer originating from the sudden high gas expansion flow at the large ignition area. The instantaneous acceleration of the vortices increases the flame surface area which gives rise to higher propagation speed; consequently, combustion time is shortened. These results suggest that the rapid increase in flame surface, caused by the large ignition area induced strong vortices, could be one of the potential methods in improving combustion efficiency by reducing the burning time in the internal combustion devices.
  • Akter Hossain, Nobuyuki Oshima, Yuji Nakamura, Marie Oshima
    JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 4 2 226 - 237 2009年 [査読有り][通常論文]
     
    In this study, an in-line pre-heating effect on the propagation of a laminar premixed flame in a two-dimensional channel is investigated numerically. An in-line pre-heating thickness of 1mm is generated by imposing uniform external high-temperature along the center line in the prescribed channel. It is found that the shapes of flame and propagation speeds are strongly affected by the pre-heating effect. The distribution of velocity pointed to ahead of the propagating flame (called negative velocity hereafter) is clearly observed which is susceptible to the generation of the pair of vortex in ahead of the flame tip. The evolution of negative flow field in front of premixed flame is successfully captured first ever in a time-dependent manner. The obtained flame propagation accompanied with the aforementioned negative velocity field is not only useful to elucidate the laser induced flame instability reported recently by Tsuchimoto et al. (2007), but also to consider the pure thermal effect on flame evolution, which is hard to obtain experimentally.
  • Yudai KANEKO, Mitsunori ITOH, Akihito KAKIKURA, Kazuhiro MORI, Kenta UEJIMA, Takuji NAKASHIMA, Masashi WAKITA, Tsuyoshi TOTANI, Nobuyuki OSHIMA, Harunori NAGATA
    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN 7 ists26 Pa_77 - Pa_80 THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 2009年 [査読有り][通常論文]
     
    A series of static firing tests was conducted to investigate the fuel regression characteristics of a Cascaded Multistage Impinging-jet (CAMUI) type hybrid rocket motor. A CAMUI type hybrid rocket uses the combination of liquid oxygen and a fuel grain made of polyethylene as a propellant. The collision distance divided by the port diameter, H/D, was varied to investigate the effect of the grain geometry on the fuel regression rate. As a result, the H/D geometry has little effect on the regression rate near the stagnation point, where the heat transfer coefficient is high. On the contrary, the fuel regression rate decreases near the circumference of the forward-end face and the backward-end face of fuel blocks. Besides the experimental approaches, a method of computational fluid dynamics clarified the heat transfer distribution on the grain surface with various H/D geometries. The calculation shows the decrease of the flow velocity due to the increase of H/D on the area where the fuel regression rate decreases with the increase of H/D. To estimate the exact fuel consumption, which is necessary to design a fuel grain, real-time measurement by an ultrasonic pulse-echo method was performed.
  • Wanyuan Shi, Eru Kurihara, Nobuyuki Oshima
    JOURNAL OF POWER SOURCES 182 1 112 - 118 2008年07月 [査読有り]
     
    in order to investigate the effect of capillary pressure on the transport of liquid water in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell, a one-dimensional steady-state mathematical model was developed, including the effect of temperature on the capillary pressure. Numerical results indicate that the liquid water saturation significantly increases with increases in the operating temperature of the fuel cell. An elevated operating temperature has an undesirable influence on the removal of liquid water inside the GDL. A reported peculiar phenomenon in which the flooding of the fuel cell under a high operating temperature and an over-saturated environment is more serious in a GDL combined with a micro-porous layer (MPL) than in a GDL without an MPL [Lim and Wang, Electrochim. Acta 49 (2004), 4149-4156] is explained based on the present analysis. (c) 2008 Elsevier B.V. All rights reserved.
  • TSUBOKURA Makoto, NAKASHIMA Takuji, IKENAGA Takeshi, ONISHI Keiji, KITOH Kozo, OSHIMA Nobuyuki, KOBAYASHI Toshio
    SAE Tech Pap Ser (Soc Automot Eng) 9  2008年04月 [査読有り][通常論文]
  • Hossain Akter, 大島 伸行, 大島 まり
    生産研究 60 1 67 - 70 東京大学 2008年01月 
       In this study, we have conducted a numerical study on the behaviors of flame in a channel influenced by ignition zone and preheating phenomenon. A system of two-dimensional governing equations for reacting flows, evolved through a single step irreversible chemical reaction between ethylene and oxygen, is solved by using Front flow Red based on the low Mach number approximation. It is found that both ignition zone and preheating phenomenon are very sensitive to the shapes of flame and their propagation speed. [This abstract is not included in the PDF]
  • Toshio Kobayashi, Makoto Tsubokura, Nobuyuki Oshima
    J. Vis. 11 1 23 - 32 2008年
  • Wanyuan Shi, Nobuyuki Oshima, L. Kumar Saha, Eru Kurihara
    MICRONANO2008-2ND INTERNATIONAL CONFERENCE ON INTEGRATION AND COMMERCIALIZATION OF MICRO AND NANOSYSTEMS, PROCEEDINGS 385 - 391 2008年 [査読有り]
     
    In order to investigate the effect of operation temperature on the liquid water removal in the polymer electrolyte fuel cell, a one-dimensional steady state mathematical model was developed for the cathode gas diffusion layer (GDL). Numerical results indicate that liquid water saturation significantly increases with increases in the operating temperature of the fuel cell because the capillary pressure in the hydrophobic GDL decreases with increasing temperature. An elevated operating temperature has an undesirable influence on the removal of liquid water inside the GDL. A reported peculiar phenomenon in which the flooding of the fuel cell under a high operating temperature and an over-saturated environment is more serious in a GDL combined with a micro-porous layer (MPL) than in a GDL without an MPL (Lim and Wang, Electrochimica Acta, 49, pp. 4149-4156,2004) is explained based on the present analysis.
  • Kang-Bin Lei, Kiwamu Kase, Nobuyuki Oshima, Toshio Kobayashi
    PROGRESS IN COMPUTATIONAL FLUID DYNAMICS 8 7-8 413 - 423 2008年 [査読有り][通常論文]
     
    Large Eddy Simulation (LES) of fully developed particle-laden turbulent channel flows were performed at Reynolds number 180 and 644, respectively. The effects of Stokes numbers, turbulent flows SGS fluctuations and inter-particle collisions on the distributions of solid particles were discussed. It was verified that, regardless of the Reynolds number of fluid flows, the maximum departure from randomness is when the ratio of the particle's aerodynamic response time to the Kolmogorov time scale of flow was approximately one. In addition, the simulation results showed that the degrees of particle preferential concentration are selectively associated with the SGS fluctuations of fluid turbulence.
  • Litan Kumar Saha, Eru Kurihara, Wanyuan Shi, Nobuyuki Oshima
    PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, PTS A AND B 1317 - 1325 2008年 [査読有り][通常論文]
     
    The flow behavior in the separator channel and gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) has been investigated by using a transient, isothermal and three-dimensional numerical model. Gas channel and gas diffusion layers are considered as the important parts of PEFC as they transport reactant gases to the catalyst layer and also byproduct from the catalyst layer. The deformation of GDL plays an important role on the performance of polymer electrolyte fuel cell since the physical properties such as porosity and permeability of the GDL and the cross sectional area of the gas channel are affected by the structural deformation of GDL. In this present investigation, non-uniform deformations shape of GDL arc taken into consideration and chosen as in the experimental data. Numerical simulations are performed for a wide range of porosity and permeability values. Further, the effects of these parameters on the pressure distribution are measured. It is revealed that the increase of porosity and permeability parameter caused the decrease of pressure drop (difference of pressure from inlet and outlet) but the decreasing rate is not uniform. It is also found that there is an effective range of porosity and permeability values for which these parameters have a very strong effect on the pressure drop. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.
  • 鬼頭 幸三, 坪倉 誠, 中島 卓司, 大島 伸行, 山本 誠, 張 会来, 大西 慶治, 小林 敏雄
    自動車技術会論文集 = Transactions of Society of Automotive Engneers of Japan 38 6 297 - 303 自動車技術会 2007年11月25日 [査読有り][通常論文]
  • 姜 玉雁, 加藤 千幸, 大島 伸行, 坪倉 誠, 張 会来
    日本ガスタービン学会誌 35 4 269 - 274 公益社団法人日本ガスタービン学会 2007年07月20日 [査読有り][通常論文]
  • TSUBOKURA Makoto, KITOH Kozo, OSHIMA Nobuyuki, NAKASHIMA Takuji, ZHANG Huilai, ONISHI Keiji, KOBAYASHI Toshio
    SAE 2007 Transactions Journal of Passenger Cars : Mechanical Systems Section 6 40 - 49 2007年04月 [査読有り][通常論文]
  • Kangbin Lei, Nobuyuki Oshima, Kiwamu Kase, Toshio Kobayashi
    FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B 823 - 831 2007年 [査読有り][通常論文]
     
    In order to study the effects of turbulence sub-grid-scale (SGS) fluctuation on particle Lagrangian motion in turbulent flows, a dynamic random walk (DRW) SGS coupling model based on an Eulerian-Lagrangian approach was developed. The advantage of the new model is that the Gaussian statistical distribution and local isotropic properties of turbulence SGS fluctuation can be parameterized by Germano's (199 1) Eulerian dynamic procedure. Using the present model, large eddy simulation (LES) was performed for downward channel flow at a Reynolds number of 180, as in the direct numerical simulation (DNS) done by Rouson & Eaton in 1997. Through a comparing of the statistical properties of particle diffusion with DNS, the capabilities and limitations of the present DRW SGS model were verified. Moreover, it was found that turbulence SGS fluctuation was strongly associated with particle motion, because preferred particles were affected by the preferred length scale of the eddy structure around. It was also found that turbulence SGS fluctuations are indispensable in calculating particles' Lagrangian trajectories in LES even when the particle Stokes number is high.
  • Hossain Akter, 大島 伸行, 大島 まり
    生産研究 59 1 59 - 62 東京大学 2007年01月 
       In this study, the effect of external heat source on the propagation of premixed flame is investigated in micro and normal gravity by two-dimensional laminar flow simulation under low Mach number approximation. Fundamental results are observed where the flame shapes and their propagation speeds are affected by the variation of gravity level in presence of external heat source. The results are useful not only to investigate the flame instability mechanism, but also to develop an efficient flame model and numerical method to simulate the effect of local temperature variation due to radiation, heat transfer and convection on the propagation of premixed flame in multi-scale physics. [This abstract is not included in the PDF]
  • Masaya Muto, Marie Oshima, Nobuyuki Oshima
    9th International Symposium on Fluid Control Measurement and Visualization 2007, FLUCOME 2007 3 1633 - 1640 2007年 
    The drag coefficient of solid particles falling in the air has been investigated experimentally. Small spherical particles free-fall through still or turbulent flow in which the turbulent level is kept constant with rotating grids as a turbulent generator. Averaged flow property that is changed depending on the charge of the particles is measured by means of LDV. Particle velocity is measured by means of 2D-PTV with laser sheet and CMOS camera. In still flow, by increasing particle volume fraction (up to O(10 )) the drag force for each particle changes, while in the turbulent flow the drag force for each particle is changed with the change of volume fraction but is relatively insensitive to turbulent intensity. Consequently, the existing empirical drag coefficient for solid particle, which depends only on the particle Reynolds number, is insufficient and it depends on the volume fraction of solid particles and ambient turbulent statistics. -3
  • Wanyuan Shi, Nobuyuki Oshima, Nobuyuki Imaishi
    PROCEEDINGS OF THE ASME/JSME THERMAL ENGINEERING SUMMER HEAT TRANSFER CONFERENCE 2007, VOL 3 19 - 23 2007年 [査読有り]
     
    Theemocapillary convection in a shallow annular pool (depth d =1 mm) of silicone oil (0.65 cSt, Pr = 6.7), heated from the inner wall, is investigated by numerical simulations. Under a fixed value of temperature difference between the outer and inner walls, surface temperature gradient in the inner heated pool is about 10% higher than that in the outer heated pool. Accordingly, the critical temperature difference for the incipience of HTW (Delta T-c=4.58K) is smaller than that (Delta T-c =5.0K) in the outer heated pool. Numerical simulations indicate that two groups of HTW, propagating in opposite azimuthal directions to each other, coexist and produce interference patterns in the inner heated pool. Rotation of the pool around its axis gives no significant influence on the behavior of HTW in the inner heated pool. The characteristics of HTW are discussed in contrast with those in the outer heated pool.
  • Makoto Tsubokura, Takuji Nakashima, Nobuyuki Oshima, Kozo Kitoh, Huilai Zhang, Keiji Onishi, Toshio Kobayashi
    FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT ASME/JSME FLUIDS ENGINEERING SUMMER CONFERENCE, VOL 2, PTS A AND B 1191 - 1197 2007年 
    The world's largest class unsteady turbulence simulations flow around vehicles were conducted using Large Eddy Simulation (LES) on the Earth Simulator in Japan. The main objective of our study is to investigate the validity of LES, as an alternative to a conventional wind tunnel measurement or the Reynolds Averaged Navier-Stokes method, for the assessment of vehicle aerodynamics.
  • Jun Arai, Marie Oshima, Nobuyuki Oshima, Hisashi Ito, Masato Kubota
    SAE Technical Papers 2007年 [査読有り][通常論文]
     
    The behavior of spray injections to turbulent duct flows from a slit injector for direct-injection gasoline engines was investigated using a combination of large eddy simulation (LES) and Lagrangian discrete droplet model (DDM). As a result, diffusion of droplets in stronger turbulent flows was observed at a later stage of the injection. Moreover, we compared calculation and experimental results by generating a pseudo-particle image from the calculation result. Copyright © 2007 SAE International.
  • Feng-Chen Li, Masamichi Oishi, Yasuo Kawaguchi, Nobuyuki Oshima, Marie Oshima
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 31 3 237 - 248 2007年01月 [査読有り][通常論文]
     
    In this study, we have investigated the influence of viscoelasticity on symmetry breaking of swirling cylinder flows with free surface driven by the constant rotation of bottom wall. Particle-image velocimetry was used to measure the in-plane velocity field in the meridional plane and horizontal planes at different heights for a constant aspect ratio (H/R = 2) cylinder flow. The tested fluids were water and aqueous solutions of CTAC/NaSal (CTAC - cetyltrimethyl ammonium chloride; Nasal - sodium salicylate) with 30 ppm (ppm - part per million), 100 ppm and 200 ppm weight concentration of CTAC. For water and 30 ppm CTAC solution (with very weak viscoelasticity) flows, symmetry breaking at the state of azimuthal rotating waves occurred from an onset Reynolds number. For 100 ppm and 200 ppm CTAC solutions (with relatively strong viscoelasticity), the flow never became. steady at the presently measured conditions: Reynolds number ranging from 750 to 4000 and Wessenberg number ranging from 0.25 to 2.20; no organized vortex structures and clear symmetry-breaking mode as appeared in water flow were observed. If any, the symmetry breaking influenced by relatively strong viscoelasticity was in a random mode. (C) 2006 Elsevier Inc. All rights reserved.
  • Feng-Chen Li, Masamichi Oishi, Yasuo Kawaguchi, Nobuyuki Oshima, Marie Oshima
    PROCEEDINGS OF THE ASME FLUIDS ENGINEERING DIVISION SUMMER CONFERENCE, VOL 1, PTS A AND B 1561 - 1569 2006年 [査読有り][通常論文]
     
    An experimental investigation was performed on the swirling flow of viscoelastic fluid with deformed free surface in a cylindrical container driven by the constantly rotating bottom wall. The tested fluid was an aqueous solution of CTAC (cetyltrimethyl ammonium chloride), which is a cationic surfactant. Water, 40ppm, 60ppm and 200ppm CTAC solution flows were tested at Froude numbers ranging from 2.59 to 16.3. PIV was used to measure the secondary velocity field in the meridional plane and the deformed free-surface level was extracted from the PIV images. At a similar Froude number, the depth of the dip formed at the center region of the free surface was decreased for CTAC solution flow compared with water flow. The inertia-driven vortex at the up-right corner in the meridional plane becomes more and more weakened with increase of the solution concentration or viscoelasticity. Through analyzing the overall force balance compared with water flow, the first normal stress difference or the weak viscoelasticity was estimated for the dilute CTAC solution flows.
  • 鬼頭 幸三, 藤浦 義裕, 加藤 進, 戸田 和之, 山本 誠, 谷口 伸行, 張 会来, ティム ウオーカー
    生産研究 57 1 36 - 39 東京大学 2005年01月
  • 武藤 昌也, サリム エスエム ムスタバ, 谷口 伸行
    生産研究 57 1 44 - 47 東京大学 2005年01月
  • Hideo Miyachi, Marie Oshima, Yoshitaka Ohyoshi, Takehiro Matsuo, Taiki Tanimae, Nobuyuki Oshima
    First International Conference on e-Science and Grid Technologies (e-Science 2005)(e-Science) 530 - 535 2005年
  • 加藤千幸, 佐藤文俊, 中野達也, 大野隆央, 谷口伸行, 矢川元基, 小池秀よ, 奥田洋司
    化学工業 56 4 2005年
  • 伊藤 裕一, 谷口 伸行, 山田 英助
    年次大会講演論文集 2004 459 - 460 一般社団法人日本機械学会 2004年 
    Large-Eddy Stimulation (LES) of a turbulent swirling flow with dispersed droplet motion is conducted to investigate turbulence and droplet interaction in turbulent swirling flow. An experimental database for the laboratory spray combustor is chosen to validate the present numerical simulation. The governing equations for the gas phases are discretized in a three-dimensional curvilinear boundary-fitted coordinate system, and the fuel droplet motion equations are described in a Lagrangian representation. The numerical results show that highly unsteady air flow and mixture fraction distributions. The droplet velocity distribution at various locations are quatitavely agree with experimental results.
  • 谷口 伸行, 加藤 千幸, 筧 雅行, 張 会来
    生産研究 55 3 265 - 271 東京大学 2003年05月
  • 谷口 伸行, 伊藤 裕一
    年次大会講演論文集 2003 129 - 130 一般社団法人日本機械学会 2003年
  • 国崎康則, 谷口伸行, 小林敏雄
    可視化情報学会誌 23 91 2003年
  • KB Lei, N Taniguchi, T Kobayashi
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 45 1 164 - 173 2002年02月 [査読有り][通常論文]
     
    The paper presents a new dynamic SGS model of two-way coupling for large eddy simulation of particle-laden turbulent flow based on Yuu's model (1997). The advantage of this new model is that coupling of fluid-particles SGS components is taken into account and at the same time the coefficient of proposed SGS model can be optimized by Germano's (1991) dynamic procedure. To investigate the capability of this model, numerical simulations of particle-laden turbulent flow at Re=644 in a vertical channel were performed using this new dynamic SGS model and using Van Driest wall function. By comparing the calculation results with that of using single-phase SGS models, in which the coupling of SGS components was not considered, the present dynamic SGS model for two-way coupling was verified. In addition, the roles of particles GS and SGS components played in the turbulence modulation of fluid flow were clarified for particle-laden channel turbulent flows.
  • 坪倉 誠, 小林 敏雄, 谷口 伸行
    年次大会講演論文集 2002 247 - 248 一般社団法人日本機械学会 2002年 
    Three-dimensional organized structures of the plane and round impinging jets were investigated by the visualized images obtained by DNS. We especially focused on the effect of the spanwise of azimuthal disturbances imposed at the inlet velocity on the eddy structures. Three wavelength of λ/πD=1/3,1/4 and 1/6 were tested in this study, where D is the width or the diameter of the inlet nozzle. The round jet showed definite instability at λ/πD=1/6 while the plane jet was found to show almost equivalent sensitivity to all modes tested here. As regards the eddy structures at the stagnation region, famous twin vortices along the impinging plate of plane jets were reproduced and their number of pairs were found to agree well with the spanwise wave number imposed at the inlet.
  • 弘畑 幹鐘, 谷口 伸行, 小林 敏雄
    年次大会講演論文集 2002 347 - 348 一般社団法人日本機械学会 2002年 
    In this paper, We introduce model for the LES of lifted non-premixed jet flames based on 2 scalar flamelet modeling. The flamelet G-equation for premixed combustion and the conserved scalar equation for non-premixed combustion are combined to express partially premixed flame propagation. The calculation results are shown that wrinkling lifted flames are simulated and the lift-off height can be predicted. This method will be useful to investigate the flame stabilizing mechanism or flame controls of non-premixed jet flames.
  • 井上 克哉, 弘畑 幹鐘, 谷口 伸行, 小林 敏雄
    年次大会講演論文集 2002 349 - 350 一般社団法人日本機械学会 2002年 
    In this research, a Large Eddy Simulation (LES) of hydrogen jet non-premixed flame was carried out and a prediction method for nitric oxide (NO) applicable to LES was proposed. Combustion model in LES is based on conserved scalar approach and laminar flamelet model. In NO prediction method, NO source term is calculated using temperature and species concentration predicted by LES and the transport of mass fraction of NO is calculated as a passive scalar, which does not affect flow field. Computed results were found in overall agreement with experimental data in velocity and temperature field. The trend of distribution of NO concentration was predicted reasonably by using this method, however the amount was underestimated.
  • LEI K, 谷口伸行, 小林敏雄
    日本機械学会論文集 B編 68 666 2002年
  • 木枝香織, 小垣哲也, 松宮ひかる, 谷口伸行, 小林敏雄
    日本機械学会論文集 B編 68 676 2002年
  • 小林 克年, 谷口 伸行, 小林 敏雄, 岡崎 輝幸, 小林 啓信
    年次大会講演論文集 1 63 - 64 一般社団法人日本機械学会 2001年 
    Some wall stress models have been proposed to reduce the CPU time required in LES and to predict with a good accuracy. We improve the 0 equation model of the turbulent eddy viscosity in the differential equations model using the gradient Richardson number. In this model we calculated the strongly swirling flow inside the cylindrical furnace. There is no difference between the improved model and non-improved model. If the tangential mean velocities are compared between LES and the experiment, that of LES is a free-vortex-type but that of the experiment is a forced-vortex type.
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 53 1 25 - 30 東京大学 2001年01月 
    近年、固気混相流の分野において乱流変調問題や乱流中の粒子運動に対して乱流数値解析法を適用するシミュレーションが盛んになされるようになってきた。特に連続相の解析には非定常、高レイノルズ数の乱流場に対して有効なラージ・エディ・シミュレーション(LES)を、分散相の解析には個々粒子の動きを決定するラグランジュ 追跡法を用いる手法が脚光を浴びている。本報では、著者らの提案したダイナミックRandom Walk SGS モデルを用いて、さらに粒子間の衝突を考慮する決定論的DNS手法を加えてLES解析を行い、粒子ストークス数と粒子空間分布の相関、乱流のSGS成分の固体粒子密度への影響、および粒子の衝突による粒子群の形成などについて計算結果の可視化により調べた結果を述べる。
  • 坪倉誠, 小林敏雄, 谷口伸行
    日本機械学会論文集 B編 67 664 2001年
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 52 11 566 - 569 東京大学 2000年11月
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 52 8 356 - 359 東京大学 2000年08月
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 52 4 182 - 185 東京大学 2000年04月
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 52 4 205 - 208 東京大学 2000年04月
  • 胡 暉, 佐賀 徹雄, 小林 敏雄, 谷口 伸行
    可視化情報学会誌 20 1 245 - 248 The Visualization Society of Japan 2000年 
    The "classical" PIV technique is only capable of recording the projection of velocity into the plane of the laser sheet, i.e the out-of-plane velocity component is lost while the in-plane components are affected by an unrecoverable error due to the perspective transformation. For highly three-dimensional flow fields like lobed jet mixing flow, this may lead to substantial measurement error of the local velocity vector. In order to get the velocity three-components simultaneously to reveal the interaction and evolution of various vortices in the lobed jet mixing flow, a high-resolution stereoscopic PIV system is used in the present study to measure the near flow field of a lobed jet mixing flow. Based on the analyzing of the three-components and three-dimensional velocity fields of the stereoscopic PIV measurement results, the mixing characteristics in the lobed jet mixing flow is studied and the mechanism of the mixing enhancement in lobed jet mixing flow is discussed.
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    年次大会講演論文集 2000 7 - 8 一般社団法人日本機械学会 2000年 
    The paper presents a dynamic SGS model of Two Way Coupling for Large Eddy Simulation of particle-laden turbulent flow, which based on Yuu's model (2000). The advantage of this new model is that the coefficient of proposed SGS model can be decided by Germano's (1991) dynamic procedure. Then, the numerical simulation was performed with Van Driest wall function model and the present dynamic SGS model, for downward particle laden turbulent flows at Re=644 in a vertical channel. The present dynamic SGS model has been verified through comparison of statistical properties of particle-laden turbulent flow.
  • 小林 克年, 谷口 伸行, 小林 敏雄
    年次大会講演論文集 2000 1 - 2 一般社団法人日本機械学会 2000年 
    A non equilibrium fixed parameter subgrid scale model obeying with the near wall asymptotic constraint was proposed by Yoshizwa. In this research Yoshizawa model with two model constants which were optimized by using 2nd order finite difference scheme, was re assessed by using 4th order finite difference scheme proposed by Morinishi. And Yoshizawa model with the optimized model constants was applied to channel flows R_τ = 180,395,590. 4th order finite difference scheme improved the accuracy of numerical simulation in Streamwise mean velocity and GS turbulent intensity. And Yoshizawa model was better in the accuracy of numerical simulation than Smagorinsky model in 4th order finite difference scheme.
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 52 1 59 - 62 東京大学 2000年01月
  • HAN H, 田中和博, 谷口伸行, 小林敏雄
    日本機械学会論文集 B編 66 645 2000年
  • 泉元, 谷口伸行, 川田裕, 小林敏雄
    日本機械学会論文集 B編 66 644 2000年
  • 小林克年, 谷口伸行, 小林敏雄
    日本機械学会論文集 B編 66 651 2000年
  • M Tsubokura, T Kobayashi, N Taniguchi, T Kogaki
    JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 81 361 - 375 1999年05月 [査読有り][通常論文]
     
    It is well known that large- or middle-scale atmospheric turbulence is strongly affected by Coriolis force which produce particular eddy structures in the flow field. In this study, subgrid-scale modeling considering Coriolis force was presented following the method proposed by Yoshizawa et al. [Phys. Fluids 8 (1996) 2254]. The proposed subgrid-scale model was successfully applied to LES of rotating channel flows at Re-tau = 150 and 590 normalized by the channel half-width and the friction velocity and the effect of rotation at low and moderate Reynolds number was investigated. The dynamic procedure proposed by Germane et al. [Phys, Fluids A 3 (1991) 1760], was adopted to determine the model parameter dynamically depending on the flow field. The way to discretize spatial filtering operation by the finite difference method required for the procedure, to be also presented, is indispensable for the application of the method to engineering and geophysical problems. Dependence of the results on discretized filtering was also examined. (C) 1999 Elsevier Science Ltd, All rights reserved.
  • 胡 暉, 佐賀 徹雄, 小林 敏雄, 瀬川 茂樹, 谷口 伸行, 植村 知正
    可視化情報学会誌 19 2 131 - 134 The Visualization Society of Japan 1999年 
    The self-induced sloshing in a rectangular tank had been investigated experimentally by using Particle Imaging Velocimetry (PIV) technique. The instantaneous flow fields, time average results and phase average results of the PIV measurement were used to reveal the evolution of the vortical structures in the test tank. Based on the experimental result, resonated oscillation was suggested to be the mechanism of the self-induced sloshing, and the fluctuation of the inlet plane jet and the periodically shedding of the unsteady vortical structures were conjectured to be the excitation source of the self-induced sloshing.
  • 張 会来, 小林 敏雄, 谷口 伸行
    生産研究 51 1 37 - 40 東京大学 1999年01月 
    特集 乱流の数値シミュレーション(NST)その15
  • 高 相[チョル], 小林 敏雄, 谷口 伸行, 大塚 雅哉, 池川 昌弘
    生産研究 51 1 29 - 32 東京大学 1999年01月 
    特集 乱流の数値シミュレーション(NST)その15
  • 雷 康斌, 谷口 伸行, 小林 敏雄
    生産研究 51 1 49 - 52 東京大学 1999年01月 
    特集 乱流の数値シミュレーション(NST)その15
  • 伊藤 裕一, 谷口 伸行, 田中 和博, 小林 敏雄
    生産研究 51 1 25 - 28 東京大学 1999年01月 
    特集 乱流の数値シミュレーション(NST)その15
  • 小垣哲也, 小林敏雄, 谷口伸行
    日本機械学会論文集 B編 65 633 1999年
  • 張 会来, 小林 敏雄, 谷口 伸行
    生産研究 50 5 187 - 190 東京大学 1998年05月
  • 張 会来, 小林 敏雄, 谷口 伸行
    生産研究 50 4 175 - 178 東京大学 1998年04月
  • 張 会来, 小林 敏雄, 谷口 伸行
    生産研究 50 2 107 - 110 東京大学 1998年02月
  • 張 会来, 小林 敏雄, 谷口 伸行
    生産研究 50 1 49 - 52 東京大学 1998年01月 
    特集 乱流の数値シミュレーション(NST)その14
  • 木枝香織, 谷口伸行, 松宮ひかる, 小林敏雄
    日本機械学会論文集 B編 64 622 1998年
  • 木枝香織, 谷口伸行, 松宮ひかる, 小林敏雄
    日本機械学会論文集 B編 63 614 1997年
  • 泉元, 谷口伸行, 川田裕, 小林敏雄, 足立武司
    日本機械学会論文集 B編 62 594 1996年
  • 坪倉誠, 小林敏雄, 谷口伸行
    日本機械学会論文集 B編 62 601 1996年
  • 荒川雅裕, 川橋正昭, 小林敏雄, 谷口伸行
    日本機械学会全国大会講演論文集 74th Vol 3 1996年
  • 坪倉誠, 小林敏雄, 谷口伸行
    日本機械学会論文集 B編 62 600 1996年
  • 泉元, 谷口伸行, 川田裕, 小林敏雄, 足立武司
    日本機械学会論文集 B編 60 579 1994年
  • 泉元, 谷口伸行, 川田裕, 足立武司, 小林敏雄
    日本機械学会論文集 B編 60 572 1994年
  • 谷口伸行
    機械の研究 45 1 1993年
  • 松宮ひかる, 木枝香織, 谷口伸行, 小林敏雄
    日本機械学会論文集 B編 59 566 1993年
  • 湊 清之, 柳 漢呉, 小林 敏雄, 谷口 伸行
    可視化情報学会誌 12 1 55 - 58 The Visualization Society of Japan 1992年 
    In this paper, the effect of rear body shape on the wake structure behind vehicle and on its aerodynamic characteristics is clarified. Three different rear body shapes, with the same front and center body shape, are used. The flow behavior in the wake is observed by flow visualization using Digital Image Processing and numerical results. The authors obtained results that the aerodynamic characteristics of vehicles strongly depend on the behavior of the wake.
  • 谷口伸行, 長藤友建, 小林敏雄, 鈴木敏暁, 島田尚子
    ターボ機械 20 5 1992年
  • Taniguchi, Nobuyuki, Arakawa, Chuichi, Kobayashi, Toshio
    JSME International Journal, Series 2: Fluids Engineering, Heat Transfer, Power, Combustion, Thermophysical Properties 34 1 1991年
  • 景井 高男, 谷口 伸行, 小林 敏雄
    可視化情報学会誌 10 2 125 - 128 The Visualization Society of Japan 1990年 
    In a general flow simulation of the mechanical engineering, it is usually desired that the complicated grid is interactively generated and modified by using computer graphics as to remarkably increase the efficiency of the pre-procedure for the flow simulation.
    In this paper, a routine system checking the adaptability of grid is developed to indicate any intersection, concentration, orthogonality, inclination and so on, and visual examples are displayed for the grid around the formula car with wheels.
    The procedure is executed efficiently on a graphic computer of TITAN.
  • 谷口伸行, 荒川忠一, 小林敏雄
    日本機械学会論文集 B編 55 513 1989年
  • 谷口伸行, 荒川忠一, 小林敏雄, 田古里哲夫
    日本機械学会論文集 B編 55 518 1989年

書籍

  • コンピュータによる流体力学
    シュプリンガー・フェアラーク東京 2003年
  • Computational Methods for Fluid Dynamics
    2003年

その他活動・業績

共同研究・競争的資金等の研究課題

  • LESを用いた燃焼器の燃焼解析手法の開発
    受託研究
    研究期間 : 2004年
  • 固体高分子燃料電池の流動・物質拡散数値シミュレーションの研究開発
    新エネルギー技術研究開発費
    研究期間 : 2004年
  • 革新的シミュレーションソフトウェアの開発
    科学技術振興調整費による重点基礎研究
    研究期間 : 2004年

教育活動情報

主要な担当授業

  • 計算流体工学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : Numerical simulation, Fluid mechanics, Turbulence models, Numerical error analysis, Computer-aided engineering
  • 流体工学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : Fluid engineering, Theory of thermal-fluid mechanics, Computational fluid mechanics, Flow measurement & visualization, Food Science
  • 計算流体工学特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : Numerical simulation, Fluid mechanics, Turbulence models, Numerical error analysis, Computer-aided engineering
  • 流体工学特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • 流体力学Ⅱ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 流体力学、ナビエ・ストークス方程式、粘性抵抗,レイノルズ数、境界層、剥離、抗力、乱流
  • 計算工学B
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : CAE、数値計算、差分法、流体力学

大学運営

委員歴

  • 2006年 - 2008年   伝熱学会   理事   伝熱学会
  • 2006年 - 2008年   可視化情報学会   代議員   可視化情報学会
  • 2006年   日本自動車技術会   CFD技術部門委員   日本自動車技術会
  • 2006年   日本機械学会   流体工学部門技術委員会 講演会WG主査   日本機械学会


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