研究者詳細 - 坪井　伸幸

論文 - 坪井　伸幸

分割表示254 件中 61 - 80 件目／全件表示 >>

異種分子間相互作用の影響に注目した酸水素混合系に対するcubic型状態方程式の第一原理的検証

髙橋竜二, 坪井伸幸, 徳増崇, 渡邉聡, 津田伸一

年次大会 ( 一般社団法人日本機械学会 ) 2019 ( 0 ) 2019年01月

記述言語：日本語掲載種別：研究論文（研究会，シンポジウム資料等）

In compressible computational fluid dynamics (CFD) analyses for combustion chamber of liquid rocket engine, the combination of cubic type equation of state (EOS) and classical mixing rule (CMR) is mostly used as typical EOS for mixture system. However, validation of the EOS for the mixture of liquid rocket propellant has hardly been validated due to lack of experimental data. Previously, validation of cubic type EOS with CMR was conducted by molecular simulation applying an ab-initio intermolecular potential as a quantum chemical approach. However, the accuracy of the H2-O2 potential is questionable because it was constructed on the basis of molecular orbital (MO) calculation for some limited molecular orientations. Therefore, in this study, we performed MO calculations for more molecular orientations between H2-O2 and reconstructed the intermolecular potential on the basis of the results of MO calculations with CCSD(T)/augcc-PVQZ level of theory. Next, we revalidated cubic type EOS coupled with CMR by evaluating the thermophysical properties of supercritical oxygen-hydrogen mixture system using Monte Carlo (MC) simulations applying the improved H2-O2 potential. As a result, we confirmed that cubic type EOS coupled with CMR can roughly reproduce the thermophysical properties obtained from MC simulation. Therefore, it was suggested that cubic type EOS with CMR can be applied to CFD analyses for combustion chamber of liquid rocket engine.

DOI： 10.1299/jsmemecj.2019.J05412

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007816327

メタン/酸素予混合気におけるデトネーションセル構造の新たな可視化方法とギャッロッピングデトネーションの速度振動の詳細計測に関する研究

久門昂平, 小澤晃平, 坪井伸幸, 林光一

日本機械学会九州支部講演論文集 ( 一般社団法人日本機械学会 ) 2019 ( 0 ) 2019年01月

記述言語：日本語掲載種別：研究論文（研究会，シンポジウム資料等）

In order to understand the detailed mechanism of galloping detonation of methane and oxygen, efforts were made to improve the cellular structure and propagation velocity of unsteady detonation. Firstly, as an alternative to smoked foil method, a new visualization of cell structure was attempted using CB film, mylar film covered by carbon black with spray-type adhesive. CB film succeeded in recording cell structure, and this result suggests a potential to apply for image recognition of the cell structure using strong backlight at scanning CB film. Secondly, the correlation between the cell structure and the propagation velocity in a galloping detonation was investigated by combining the detonation velocity measurement and smoked foil method. The propagation velocity distribution was measured using twice the sampling points in the same detonation tube length as in our previous research. This experiment revealed that, after the over-driven detonation started to decelerate, small non-uniform cell structure was formed and transited to spinning mode during the deceleration. Consequently, in galloping detonation, a strong correlation was found between wave-front acceleration and cell structure.

DOI： 10.1299/jsmekyushu.2019.72.D13

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007801952

Real-time regression rate measurement of an additive-manufactured functional hybrid rocket fuel 査読有り

Ozawa K., Wang H.W., Yoshino T., Tsuboi N.

Proceedings of the International Astronautical Congress, IAC 2019-October 2019年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. The function of real-time fuel regression integrated into an additively-manufactured hybrid rocket fuel was conceptually demonstrated by firing experiments. This fuel has a complex ladder resistor structure made of a plastic filament including conductive additives in an electrically insulated main plastic fuel. The real-time regression rate measurement is enabled by the change of the voltage applied to the ladder resistor structure when the top rung is broken by the fuel regression. This type of fuel has advantages in the easy acquisition of the distribution of the local regression rates with a greatly small pitch, minimizing the influences on the structural mass, propulsive performance, and fuel regression behavior especially when loading such a measurement system on space vehicles. Prototype slab fuels outputted steep changes in the voltage indicating the break of the rungs when using rungs with the thickness of 0.15 mm in firing experiments. The acquired breaking signals with the positions of the rungs were compared with the results of the fuel surface detection in the high-speed videos. In 3 of 4 successful experiments, the sensing system of the proposing measurement method followed the fuel regression detected by the high-speed videos within 0.5 mm errors, which are in the same range as the roughness of the solid fuels after the burns. The time history of the breaking signals showed a fuel regression at an almost constant rate. The difference of the steady-state regression rates was less than 0.06 mm/s between these two methods, except for run #4, 0.094 mm/s. It was also confirmed that the ladder resistor structures can be a heater to warm the main solid fuel when applying a voltage larger than 5 V to the resistor structure. This function is also useful for the thermal management of solid fuels in space.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85079135960&origin=inward

Boundary-layer combustion of wax-based fuels at various chamber pressures under two static acceleration environments 査読有り

Ozawa K., Yoshino T., Wang H.W., Tsuboi N.

AIAA Propulsion and Energy Forum and Exposition, 2019 2019年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

© 2019 by American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Boundary layer combustion of wax-based fuels was visualized under atmospheric and supercritical chamber pressures under vertical and horizontal setups. The final goal of this research is to clarify the effects of acceleration environments on the performance of wax-based fuels. At the atmospheric pressure, the roll waves of the melted fuel excited propagated over the fuel top surface, and fuel droplets were entrained by the main gaseous flow for the horizontal setup. However the propagation of the roll waves covered at most 55% of the fuel to surface, and the entrained fuel droplets were hardly observed for the vertical setup. Above the critical pressure, the instabilities of the melted fuel were observed for both setups, but it was difficult to find any differences in the behaviors of the melted fuel due to the strong radiation of the fuel-rich flame on the melted fuels even after the various improvements of the optical system and the solid fuel. At supercritical pressures, the diffusion flames and the melted fuels oscillated at the frequency of approximately 600 Hz by sight, which is approximately the same with the natural frequency of the TCG coupling mode. The fast Fourier transformation up to 500 Hz output an intense peak of approximately 311 Hz for all runs with the horizontal setup and the sonic nozzle. A slight difference in the fuel regression behavior was found between the two burner setups. The vertically set burner showed the larger regression rates at supercritical conditions whereas the regression exponent for the horizontal setup agreed with that of existing data with a horizontally set motor. This result suggests body force increases the mass flow rate of the melted fuel film, which was not considered as a fuel mass transfer in the current liquefying hybrid theory.

DOI： 10.2514/6.2019-4100

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85084097288&origin=inward

Numerical Study on Aerodynamic Characteristics of Reusable Vehicle-eXperiment Rocket with Body-flap during Gliding

Yoshiki Nishikawa, Nobuyuki Tsuboi, Takashi Ito, Satoshi Nonaka

15th International Conference on Flow Dynamics GS1-30 2018年11月

Statistical mechanical evaluation of thermophysical properties of oxygen-hydrogen mixture system based on the differential hierarchy of a complete thermodynamic function

Ryuji Takahashi, Nobuyuki Tsuboi, Takashi Tokumasu and Shin-ichi Tsuda

Fifteenth International Conference on Flow Dynamics CRF-58 2018年11月

Numerical Simulations of Hydrogen Jet Mixing in Supersonic Crossflow for Liquid Rocket Commanded Destruction

Toshihiro Iwasa, Keiichiro Fujimoto, Daiki Muto, Nobuyuki Tsuboi

12th Asian Computational Fluid Dynamics Conference 0104 2018年10月

Two-Dimensional Numerical Simulation of Detonation Transition with Multi-Step Reaction Model: Effects of Obstacle Height 査読有り

A. Ago, N. Tsuboi, E. Dzieminska, A. K. Hayashi

Combustion Science and Technology 191 659 - 675 2018年08月

Numerical investigation of a high pressure hydrogen jet of 82 MPa with adaptive mesh refinement: Concentration and velocity distributions 査読有り

Tang X., Dzieminska E., Asahara M., Hayashi A., Tsuboi N.

International Journal of Hydrogen Energy 43 ( 18 ) 9094 - 9109 2018年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2018 Hydrogen Energy Publications LLC To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale lTand direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen CH2on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation σˆH2asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of σˆH2is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial CH2agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration C¯H2along the radial directions can also be described as a Gaussian distribution. The axial C¯H2of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with C¯H2=4200/(z/θ) where z is the axial distance from the nozzle and θ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration Ztipis found to be in a linear relationship with the square root of jet flow time t. Meanwhile, the jet's velocity half-width LVhapproximately gains an linear relation with z which can be expressed as LVh=0.09z.

DOI： 10.1016/j.ijhydene.2018.03.089

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85045105507&origin=inward

Three-dimensional numerical simulation on hydrogen-oxygen rotating detonation engine with unchoked aerospike nozzle 査読有り

Tsuboi N., Jourdaine N., Watanabe T., Koichi Hayashi A., Kojima T.

AIAA Aerospace Sciences Meeting, 2018 ( 210059 ) 2018年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The present study simulates three-dimensional rotating detonation engine with an unchoked aerospike nozzle geometry for hydrogen/oxygen gas mixture to understand the advantages to use the aerospike nozzle on the thrust performance. The gonverning equations uses the unsteady three-dimensional compressible Euler equations with the detailed chemistry model. The oblique shock wave propagates along the coaxial combustion chamber and outside of the nozzle exit. The exhaust jet under atmospheric condition is slightly underexpanded and some complicated and unsteady shock waves are formed in the plume. The degree of the expansion in the exaust flow increases as the stagnation pressure increases. The effects of the stagnation pressure on the thrust performance indicate that Isp increases 270s for p0= 4 MPa although Isp for p0= 1.5 MPa is 220s. The time-averaged thrust is proportional to the injected mass flow and this feature is different from those without the external regions.

DOI： 10.2514/6.2018-1885

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85044438502&origin=inward

Visualization of boundary layer combustion of wax-based fuels in vertical and horizontal configurations 査読有り

Ozawa K., Yoshino T., Tsuboi N.

2018 Joint Propulsion Conference 2018年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Efforts have been carried out from both the theoretical and experimental approaches to reveal the effects of body force parallel to the main flow on the diffusion flame in hybrid rocket propulsion with entrainment of liquid fuel droplets. A theoretical study on liquefying fuels such as wax fuels were partially extended for static acceleration environments and acquired interesting results that the static body force scarcely affects the internal ballistics of the entrained fuel droplets but it can affect the thickness of the liquid fuel layer and the fuel regression rate of the entrained droplets. Diffusion flame of two wax fuels at the atmospheric pressure has been visualized with a slab burner and a high-speed camera in the horizontally and vertical configurations to change the body force loaded to the fluid in the slab burner. The instability of the diffusion flames looked similar to each other over all the experiments, and the high-speed video has observed a few burning droplets entrained from the liquid fuel layer in each of the experiments. The monitoring camera observed a lot of unburned fuel droplets from the slab burner vertically installed.

DOI： 10.2514/6.2018-4928

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85066478484&origin=inward

Validation of classical mixing rule coupled with a van der Waals-type equation of state for supercritical mixture system of oxygen and hydrogen using molecular simulation 査読有り

TAKAHASHI Ryuji, TSUBOI Nobuyuki, TOKUMASU Takashi, TSUDA Shin-ichi

Mechanical Engineering Letters 2018年01月

Numerical prediction of forced-ignition limit in high-pressurized hydrogen jet flow through a pinhole 査読有り

Makoto Asahara, Nobuyuki Tsuboi, N., Fujimoto, K., Muto, D., Hayashi, A.K.

Intermational Conference on Hydrogen Safety ID193 2017年09月

A molecular dynamics study of nuclear quantum effect on diffusivity of hydrogen molecule 査読有り

Nagashima H., Tsuda S., Tsuboi N., Hayashi A., Tokumasu T.

Journal of Chemical Physics 147 ( 2 ) 2017年07月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 Author(s). In this paper, the nuclear quantum effect of the hydrogen molecule on its diffusivity was analyzed using the molecular dynamics (MD) method. The centroid MD (CMD) method was applied to reproduce the time evolution of the molecules. The diffusion coefficient of hydrogen was calculated using the Green-Kubo method over a wide temperature region, and the temperature dependence of the quantum effect of the hydrogen molecule on its diffusivity was addressed. The calculated results were compared with classical MD results based on the principle of corresponding state (PCS). It was confirmed that the difference in the diffusion coefficient calculated in the CMD and classical MD methods was small, and the PCS appears to be satisfied on the temperature dependence of the diffusion coefficient, even though the quantum effect of the hydrogen molecules was taken into account. It was clarified that this result did not suggest that the quantum effect on the diffusivity of the hydrogen molecule was small but that the two changes in the intermolecular interaction of hydrogen due to the quantum effect offset each other. Moreover, it was found that this tendency was related to the temperature dependence of the ratio of the kinetic energy of the quantum fluctuational motion to the classical kinetic energy.

DOI： 10.1063/1.4991732

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85024090367&origin=inward

Numerical Study on Effects of Obstacle Shape on Detonation Transition Mechanism 査読有り

A. Ago, T. Niibo, N. Tsuboi, A.K. Hayashi

26th International Colloquium on the Dynamics of Explosions and Reactive systems 1027 2017年07月

Numerical Analysis on Liquid JP10 Rotating Detonation Engine 査読有り

A.K. Hayashi, W. Yoshida, M. Asahara, N. Tsuboi

26th International Colloquium on the Dynamics of Explosions and Reactive systems 2017年07月

Two-Dimensional Numerical Analysis on Shock Flame Interaction in Premixed Gas of Hydrocarbon/Oxygen with Multi-Step Reaction Model 査読有り

M. Iwai, K. Yoshida, Y. Morii, N. Tsuboi, A.K. Hayashi

26th International Colloquium on the Dynamics of Explosions and Reactive systems 1050 2017年07月

Experimental Study on Behavior of Methane/Oxygen Gas Detonation Near Propagation Limit in Small Diameter Tube: Effects of Equivalent Ratio 査読有り

K. Yoshida, T. Inoue, Y. Morii, K. Murakami, N. Tsuboi, A.K. Hayashi,

26th International Colloquium on the Dynamics of Explosions and Reactive systems 822 2017年07月

Numerical Simulations of Transverse Jet in Supersonic Crossflow toward an Understanding of Interaction Mechanism 査読有り

Toshihiro Iwasa, Keiichiro Fujimoto, Daiki Muto, Nobuyuki Tsuboi

31st International Symposium Shock Waves 2017年07月

Numerical investigation of a high pressure hydrogen jet of 82 MPa with adaptive mesh refinement: The starting transient evolution and Mach disk stabilization 査読有り

Tang X., Asahara M., Hayashi A., Tsuboi N.

International Journal of Hydrogen Energy 42 ( 10 ) 7120 - 7134 2017年03月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017A three-dimensional (3D) strongly under expanded hydrogen jet flow is numerically investigated with a storage pressure of 82 MPa and a tiny jet orifice diameter of 0.2 mm. The full compressible Navier–Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing adaptive mesh refinement (AMR) technology to reduce the number of grid cells. The highly under expanded hydrogen jet flow with a nozzle pressure ratio (NPR) of about 809 is then captured from the very beginning when hydrogen is ejected out of the jet orifice. The starting transient evolution and Mach disk stabilization are then discussed in details. It is found that with the AMR technology, the grid number can be greatly reduced and high resolutions can be easily installed to deal with the small jet orifice size together with those flow microscales. Jet flow is numerically captured and discussed. It is found that over expansion occurs in this under expanded jet. The secondary shock is generated to match the pressure which plays the most important physics in the starting transient period of an under expanded hydrogen jet. The Mach shock and the lateral barrel shock which are originated from the secondary shock play central roles. The jet flow is divided into subsonic and supersonic branches in the near-nozzle region, which makes the highly under-expanded jets have two annular shear layers, the inner and outer layer, in this region.

DOI： 10.1016/j.ijhydene.2017.01.016

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85014312065&origin=inward

　前のページ - 次のページ　

<坪井 伸幸>

論文 - 坪井 伸幸

<坪井　伸幸>

論文 - 坪井　伸幸