研究者詳細 - 坪井　伸幸

論文 - 坪井　伸幸

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Three-dimensional numerical simulation on dispersion process of unsteady high pressure hydrogen jet flow 査読有り

Tsuboi N., Fujimoto K., Muto D., Asahara M., Hayashi A.

AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting 2017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）

© 2017 by the authors.The numerical simulations on the high-pressure hydrogen jet are performed by using the unsteady three-dimensional compressible Navier-Stokes equations with multi-species conservation equations. The present numerical results show that the highly expanded hydrogen free jet observes and the distance between the Mach disc and the nozzle exit agrees well with the empirical equation. The time-averaged H2 concentration of the numerical simulations agrees well with the experimental data and the empirical equation. The unsteady feature in the present numerical simulation shows that the PDF of the numerical simulations does not agree with the Gaussian PDF because the jet flow is “potential core” flow at x = 60 mm. Although higher hydrogen concentration is observed at x = 120 mm, the PDF in the numerical simulations agrees well with the Gaussian PDF at x = 180 mm. The numerical simulation of ignition in hydrogen jet is performed to show that the calculated OH distribution becomes isotropic expansion in the initial stage; however, OH flows along the leeward direction.

DOI： 10.2514/6.2017-1232

Scopus

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Numerical simulation for effects of pressure on cryogenic coaxial jet under supercritical pressure 査読有り

Araki T., Muto D., Terashima H., Tsuboi N.

AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting 2017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）

© 2017 by Rolls-Royce North America Holdings Inc.Three-dimensional numerical simulations of coaxial nitrogen jet mixing under supercritical pressures are performed with an emphasis on the effects of pressure on the mixing. The results show that the overall mixing behaviors are similar in terms of normalized density profiles between 5 and 12 MPa. However, the normalized temperature profiles are different between two conditions because non-linear change of the density to the temperature near the critical point. The peak of the constant pressure specific heat is particularly observed in the case of 5 MPa. The density and temperature fluctuations become large between the inner jet flow and the outer jet flow. Although the density fluctuation distributions are similar between two cases, the larger fluctuation region of temperature is observed in the case of 5 MPa. This is because the temperature increases are different near the critical temperature between two pressure conditions.

DOI： 10.2514/6.2017-1108

Scopus

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Front cellular structure and thrust performance on hydrogen-oxygen rotating detonation engine 査読有り

Tsuboi N., Eto S., Hayashi A., Kojima T.

Journal of Propulsion and Power 33 ( 1 ) 100 - 111 2017年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

Copyright © 2016 by the authors.Numerical simulations of three-dimensional rotating detonation engines for a hydrogen-oxygen mixture are performed using the detailed chemistry model. The grid-resolution study indicates that the cellular structure of the detonation appears near the inner wall as the circumferential grid resolution increases. However, the effects of the grid resolution are small on Isp. The grid resolution for the high-mass-flow cases should be carefully considered because the rotating detonation velocity increases to produce higher thrust under the low grid resolution. As the annular width increases, a complicated shock structure such as a Mach stem appears, and the cycle time decreases. The effects of the annular width are smallon Isp. As the number of the rotating detonations increases, the asymmetric detonation heads rotate along the circumferential direction with the same cycle time after 30 cycles. Isp for the two-waved rotating detonation engine decreases approximately 10% less than Isp for the one-waved rotating detonation engine. This is because the injected mixture mass flow rate for the two-waved rotating detonation engine increases 16% larger than that for the one-waved rotating detonation engine, whereas the thrusts between them coincide.

DOI： 10.2514/1.B36095

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85012165231&origin=inward

Three-Dimensional Numerical Simulation of a Rotating Detonation Engine: Effects of the Throat of a Converging-Diverging Nozzle on Engine Performance 査読有り

Eto S., Tsuboi N., Takayuki K., Hayashi A.

Combustion Science and Technology 188 ( 11-12 ) 2105 - 2116 2016年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2016 Taylor & Francis.The effect of a converging-diverging nozzle on the performance of a rotating detonation engine was estimated using three-dimensional numerical simulations with a detailed chemical reaction model. The nozzle in this article is composed of a long constant cross section, a short converging section, and a diverging section. The expansion area ratios of nozzles A and B in this article are 2.0 and 1.89, respectively. The periodic exhaust oscillation due to rotating detonation is considerably reduced by nozzle A. The variation of the time-averaged pressure is approximately 0.0048 MPa and the ratio to the time-averaged value is 1.3%. For nozzle B, the variation in pressure is approximately 0.018 MPa, and the ratio to the time-averaged value is 5%. The specific impulse of nozzle A increases by approximately 11 s (3.8%) compared with the value of nozzle B.

DOI： 10.1080/00102202.2016.1213990

Scopus

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

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

Combustion Science and Technology 188 ( 11-12 ) 2012 - 2025 2016年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2016 Taylor & Francis.The unstable behavior of the detonation is an important issue in predicting detonation limits and safety problems. The present study aims to obtain information of the unstable behavior near the detonation propagating limit in methane/oxygen gas mixture for various initial pressures and tube diameters. The detonation velocity rapidly decreases near α = 1.0 and deviates from the theoretical value for α < 1.0 conditions (α = πd/λ; d: tube diameter; λ: cell width). The onset of the single-head spinning is α = 1.0. For α < 1.0 conditions, the transition to the single-head spinning from small cells and the failure of cellular patterns were observed. For α > 1.0 conditions, the propagation mode was unstable. The unstable phenomenon means that the cellular pattern repeats multi-head and single-head spinning in turn.

DOI： 10.1080/00102202.2016.1213989

Scopus

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Numerical Study on Direct Initiation of Cylindrical Detonation in H<inf>2</inf>/O<inf>2</inf> Mixtures: Effect of Higher-Order Schemes on Detonation Propagation 査読有り

Niibo T., Morii Y., Ashahara M., Tsuboi N., Hayashi A.

Combustion Science and Technology 188 ( 11-12 ) 2044 - 2059 2016年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2016 Taylor & Francis.This aim of this study is to investigate the effect of grid resolution and higher-order accuracy schemes. The size of the reaction induction zone at the time of the local explosion affects the generation of transverse cells. When the reaction zone is large, transverse cells appear. As a result, for calculations in which the grid width is small or for a higher-order scheme, such as a weighted compact nonlinear scheme (WCNS), is used, the cell size increases; an irregular cellular structure is obtained, such as that observed in experiments; and unburned gas pockets and circulation structures caused by Kelvin–Helmholtz instability appear behind the detonation front. In terms of the computational cost, the computational time of 7th-order WCNS is approximately three times that of the 2nd-order monotone upstream-centered schemes for conservation laws (MUSCL) scheme.

DOI： 10.1080/00102202.2016.1215109

Scopus

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D-08 液体燃料ロケットタンク破壊時の推進剤ジェット・主流の干渉構造に関する数値解析

岩佐聡洋, 武藤大貴, 藤本圭一郎, 坪井伸幸

日本機械学会九州支部講演論文集 2016 ( 69 ) 141 - 142 2016年03月

E-23 分子シミュレーションを用いた超臨界混合系における古典的混合則の精度検証

谷口正興, 津田伸一, 坪井伸幸

日本機械学会九州支部講演論文集 2016 ( 69 ) 215 - 216 2016年03月

Numerical Analyses on Ethylene/Oxygen Detonation with Multi-step Chemical Reaction Mechanisms: Grid Resolution and Chemical Reaction Model 査読有り

Takayuki Araki, Keisuke Yoshida, Youhi Morii, Nobuyuki Tsuboi, A. Koichi Hayashi

Combustion Science and Technology 188 ( 3 ) 346 - 369 2016年03月

Numerical simulation of jet mixing in a recessed coaxial injector at supercritical pressure 査読有り

Muto D., Terashima H., Tsuboi N.

54th AIAA Aerospace Sciences Meeting 2016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）

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

Scopus

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Numerical simulation of the effects of nozzle on thrust performance of rotating detonation engine 査読有り

Eto S., Watanabe Y., Tsuboi N., Kojima T., Hayashi A.

Science and Technology of Energetic Materials 77 ( 5-6 ) 122 - 127 2016年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

The effects of the converging-diverging (CD) nozzle on the thrust performance of the rotating detonation engine (RDE) were estimated by using the three-dimensional numerical simulations with the detailed chemical reaction model. The nozzle geometry is based on the reference of Rankin et al. The nozzle is composed of the long constant cross section, the short converging section, and the diverging section. The periodic exhaust oscillation is considerably reduced by the present CD nozzle. The pressure difference from the averaged value is approximately 1.2 % and the difference in Mach number is approximately 0.4 %. The increment of Isp using the CD nozzle is approximately 15 s. The nozzle performance is estimated via the thrust coefficient. The thrust coefficient of the CD nozzle used this study is nearly corresponded with the ideal value. The combustion efficiency of C∗ ηc∗ are obtained 92-98 % between the combustion chamber pressure of 1.2 and 2.9 MPa.

Scopus

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自由回転軸を持つ翼型を用いた円柱の抗力低減方法について査読有り

佐藤一志, 吹場活佳, 坪井伸幸

日本航空宇宙学会論文集 64 ( 3 ) 153 - 159 2016年01月

記述言語：日本語掲載種別：研究論文（学術雑誌）

A novel drag reduction method for a cylinder using a pivoted airfoil is proposed in this study. The pivoted airfoil can rotate freely on a shaft so that the airfoil can head windward. First, we conducted a water tunnel test to validate the drag reduction method. Contrary to our expectation, the airfoil did not head windward completely. The airfoil started to move from an initial angle of 0º to a stable angle of about 14º. Next, we calculated the aerodynamic force of the airfoil by a computational fluid dynamics (CFD) method. The reason the airfoil did not head windward completely was revealed. This is because the sign of the moment coefficient around the rotating shaft changes with increasing angle of attack. The CFD simulation also revealed that the drag reduction method can decrease the drag by 34%.

DOI： 10.2322/jjsass.64.153

CiNii Article

その他リンク： http://ci.nii.ac.jp/naid/130005154803

Characteristics of Jet-Mixing at Supercritical Pressure: Effects of Recess Length and Post Height 査読有り

MUTO Daiki, TERASHIMA Hiroshi, TSUBOI Nobuyuki

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN 14 ( 30 ) Pa_45 - Pa_52 2016年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.2322/tastj.14.Pa_45

CiNii Article

その他リンク： http://ci.nii.ac.jp/naid/130005172064

極低温超臨界圧下の噴流に関する流体力学とその数値解析

坪井伸幸

日本燃焼学会誌 ( 日本燃焼学会 ) 57 ( 182 ) 257 - 264 2015年11月

D121 管内高圧水素噴流による自着火機構(OS-10:火災・爆発(2))

朝原誠, 横山瑛紀, 窪田智之, 佐分利禎, 和田有司, 茂木俊夫, 坪井伸幸

熱工学コンファレンス講演論文集 2015 "D121 - 1"-"D121-2" 2015年10月

記述言語：日本語掲載種別：研究論文（その他学術会議資料等）

This paper deals with a self-ignition mechanism of high-pressure hydrogen jet in a tube filled with air. Although the self-ignition phenomenon is expected to clarify for industrial safety, the ignition mechanism in a tube still has not been known well. In this study, the direct photographs of flame behaver initiated by the self-ignition are captured by a high speed camera. The flame propagation histories are obtained from the pressure and light sensors. Additionally, a numerical simulation is performed to understand the ignition process induced by hydrogen jet in detail. As the results, a self-ignition occurs at the region where the contact surface interacts with the local high-temperature region which is built by the shock wave reflects from the sidewall of tube.

CiNii Article

その他リンク： http://ci.nii.ac.jp/naid/110010045446

Numerical simulation on low-speed hydrogen jet diffusion 査読有り

Yuki Takatori, Nobuyuki Tsuboi, Keisuke Fujimoto, Daiki Muto, Makoto Asahara

The 6th International Conference on Hydrogen Safety ID179 2015年10月

J0540307 二原子分子流体の臨界点近傍における静的・動的ゆらぎ構造の分子動力学的解析

井川祥平, 永島浩樹, 坪井伸幸, 徳増崇, 津田伸一

年次大会 : Mechanical Engineering Congress, Japan 2015 "J0540307 - 1"-"J0540307-5" 2015年09月

記述言語：日本語掲載種別：研究論文（その他学術会議資料等）

In our study, we investigated fluctuation structure of diatomic fluids around the critical point. We used molecular dynamics simulation to evaluate the principle of corresponding state of fluctuation structure of 2-center-Lennard-Jones fluid which has molecular elongation as a parameter. We evaluated the static fluctuation structure by calculating dispersion of number of molecules at divided cells and static structure factor. As results, the principle of corresponding state on the static fluctuation structure is satisfied because static fluctuation structure does not have dependence on molecular elongation. On the other hand, dynamic fluctuation structure of fluid which has longer molecular elongation disagrees with dynamic fluctuation structure of fluid which has shorter molecular elongation. Therefore, it was found that the principle of corresponding state of dynamic fluctuation structure might not be satisfied.

CiNii Article

その他リンク： http://ci.nii.ac.jp/naid/110010048952

Three-dimensional cellular structure and propagation process of spherical detonation 査読有り

R. Iida, M. Asahara, A. Hayashi, N. Tsuboi

25th International Colloquium on the Dynamics of Explosions and Reactive Systems No.273 2015年08月

Behavior of Methane/Oxygen Gas Detonation near Propagating Limit in Small Diameter Tube:Effect of Tube Diameter 査読有り

K. Yoshida, K. Hayashi, Y. Morii, K. Murakami, A. Susa, N. Tsuboi, A. Hayashi

25th International Colloquium on the Dynamics of Explosions and Reactive Systems No.139 2015年08月

3D Numerical Simulation on Rotating Detonation Engine: Effects of Converging-Diverging-Nozzle on Thrust Performance 査読有り

Seiichiro ETO, Yusuke WATANABE, Nobuyuki TSUBOI, Takayuki KOJIMA, A. Koichi HAYASHI

25th International Colloquium on the Dynamics of Explosions and Reactive Systems No.132 2015年08月

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