研究者詳細 - 坪井　伸幸

論文 - 坪井　伸幸

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Investigation of liquid n-heptane/air spray detonation with an Eulerian-Eulerian model 査読有り国際誌

Jourdaine N., Tsuboi N., Hayashi A.K.

Combustion and Flame 244 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

A two-dimensional numerical simulation of detonation in a reactive dispersed liquid droplet cloud is performed with an Eulerian-Eulerian method. This study aims to investigate the model and the effects of two-phase sub-models on the propagation of a detonation through an n-heptane spray. Firstly, the simulations are compared to the experiments conducted in the thesis of Mohamed El-Amine Benmahammed [1]. Three simulations are carried out for a mono-dispersed/one sample cloud of droplets with a mass corresponding to equivalence ratios of 0.8, 1.0, and 1.3. The Eulerian-Eulerian method predicted the experimental detonation velocity and gaseous phase thermodynamic properties with reasonable accuracy. Secondly, an investigation of the effects of the mobilization of the droplet size poly-dispersity on the detonation properties was carried out. For a droplet Sauter mean diameter of 30 µm, the effect of the number of droplet samples used for modeling the poly-dispersity modifies the front structure and detonation properties. For instance, comparing 15 samples of droplet size to a unique sample, the detonation velocity decreases by 2.0 %, and the mean detonation cell width increases by 10 %.

DOI： 10.1016/j.combustflame.2022.112278

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Effects of a Recess on Coaxial Cryogenic Injections at Supercritical Pressure 査読有り国際誌

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

Journal of Propulsion and Power 38 ( 4 ) 581 - 591 2022年01月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

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

DOI： 10.2514/1.B38552

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Difference between 2D and 3D NS calculations for RDE pressure gain 査読有り国際誌

Hayashi A.K., Nihonmatsu R., Ito T., Tsuboi N., Ozawa K., Otsuka Y., Ishii K.

AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025 2025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）

RDE pressure gain (PG) analyses by NASA group in 2018 show that PG is one of the evaluations for RDE performance problems by comparing experimental data. Our groups (Hayashi, Tsuboi, and Ishii) have started the evaluation of RDE by PG from 2022 and presented our first results in AIAA SciTech 2023, January which can improve the PG value. The present presentation will provide what can affect a big and positive value to PG value through numerical analyses.

DOI： 10.2514/6.2025-1398

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Correction: [3D Numerical Simulation on Disk Type RDE used Hydrogen-Air Premixed Gas and Non-premixed Gas with Multi-Ports Injection] (American Institute of Aeronautics and Astronautics Inc, AIAA) 査読有り国際誌

Ito T., Tsuboi N., Ozawa K., Hayashi A.K.

AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025 2025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）

Correction Notice A. Comparison of propagation transition ・No.1: Before Figure 4 shows the temperature contours of the instantaneous field for each case. case 1 and case 2, which are nonpremix cases, show more unburned gas pockets than the premix case. Another feature of the non-premix case is the presence of a thin high-temperature region on the wall behind the wavefront. Figure 5 shows the time history of pressure at the outer wall. The vertical axis is the circumferential angle and the horizontal axis is time. The detonation propagation frequency was read from this pressure history, and Case 1 to Case 3 were in an overdriven state with respect to the cj velocity. In the case4, the propagation velocity was 4% lower than the cj velocity because of three wavefronts. This is due to the pressure drop caused by the increased number of propagating wavefronts [12]. After Figure 4 shows the temperature contours of the instantaneous field for each case. In Case 1, although a clear plane wave is not generated, a small area on the outer surface contains a high-temperature and high-pressure region. Case 2 also does not produce a plane wave, and many pockets of unburned gas are observed. In Case 3, the detonation wave is flat, and a high-temperature region is also observed in the oblique shock wave area on the radial side. In Case 4, the premixed gas inflow was large, resulting in a three-wave front. Figure 5 shows the time history of pressure at the outer wall. The vertical axis is the circumferential angle, and the horizontal axis is time. The detonation propagation velocity read from this pressure history is shown in Figure 6. Case 4 has three wavefronts, so the propagation velocity is 4% lower than the CJ velocity. This is due to the pressure drop caused by the increased number of propagating wavefronts [12]. The reason for this is that the geometry of the DRDE causes the shock waves to hit curved surfaces, and the overlapping of the shock waves creates a high-pressure zone on the wall surface. ・No.2 Add the following figure (Figure presented).

DOI： 10.2514/6.2025-1974.c1

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3D Numerical Simulation on Disk Type RDE used Hydrogen-Air Premixed Gas and Non-premixed Gas with Multi-Ports Injection 査読有り国際誌

Ito T., Tsuboi N., Ozawa K., Hayashi A.K.

AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025 2025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）

A three-dimensional viscosity simulation of a rotating disk detonation engine (DRDE) using the Navier-Stokes equations with the UT-JAXA reaction mechanism for H2-air Premix and Non-premix gas is presented. The purpose of this study is to visualize the propagation pattern in the DRDE combustor, to investigate the effect of the injection method on the propagation pattern, and to evaluate its impact on stable detonation propagation and DRDE performance. The results show that the injection method affects the generation of new detonation waves, that the injection method has no significant effect on the Pressure Gain, and that DRDEs have comparable performance in Pressure Gain compared to RDEs.

DOI： 10.2514/6.2025-1974

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Two-dimensional detailed numerical simulation of ammonia/hydrogen/air detonation: hydrogen concentration effects and transverse detonation wave structure 査読有り国際誌

Kohama S., Ito T., Tsuboi N., Ozawa K., Hayashi A.K.

Shock Waves 34 ( 2 ) 139 - 154 2024年04月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Numerical simulations on ammonia/hydrogen/air detonation are performed using a detailed reaction model to investigate the cellular instability and detonation dynamics as a function of hydrogen content. The UT-LCS model that includes 32 species and 213 elementary reactions is used in the present simulations. The fifth-order target compact nonlinear scheme captured the unstable detonation dynamics and the complicated flow structure including the propagation of a sub-transverse wave. The simulation performed with different hydrogen dilutions shows that the detonation propagates at the Chapman–Jouguet velocity for all cases, and the cell size for the ammonia/hydrogen mixing ratio α=0.3 becomes approximately 10 times larger than that for α=1.0 (hydrogen/air mixture). A transverse detonation produces a finescale cellular structure on the computed maximum pressure history. This complex shock formation is similar to those of a spinning detonation and two-dimensional propane/oxygen detonation. The cellular irregularity increases with decreasing hydrogen content because ammonia destabilizes the detonation cellular structure with a reduced activation energy of more than approximately 8.

DOI： 10.1007/s00193-024-01181-6

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Study of Nozzle Choking Effect on Pressure Gain of Disc Rotating Detonation Engine 査読有り国際誌

Hayashi A.K., Otsuka Y., Ishii K., Ito T., Tsuboi N., Ozawa K.

AIAA SciTech Forum and Exposition, 2024 2024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）

The present study performs the disc-type rotating detonation engine experiments for the various mass flow with the various nozzle configuration ratio of A8/A3,2, where A3,2 and A8 denote the air slit and the nozzle exit area, respectively. The pressure gain is evaluated based on the equivalent available pressure determined from the measured thrust and the air-prenum pressure. As a results, regardless of the value of A8/A3,2, Equivalent available pressure (EAP) increases monotonically with the increase of the mass flow rate. However, for the same mass flow rate, the EAP for A8/A3,2=0.2 is about three times larger than that for A8/A3,2 =0.6 and 0.8. For A8/A3,2 = 0.2, the mass flow rate and pressure gain are positively correlated and the naximum pressure gain of -0.19 is obtained at the mass flow rate of 278 g/s. For A8/A3,2= 0.6 and 0.8, the pressure gain show a decreasing trend with increasing mass flow rate. The effect of A8/A3,2 on the pressure gain is found to responsible for the flow choking in the air slit of the combustion chamber.

DOI： 10.2514/6.2024-1034

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Two-Dimensional Detailed Numerical Simulation on Ammonia/Hydrogen/Air Detonation : Hydrogen dilution effects and sub-transverse wave structure in transverse detonation 査読有り国際誌

Shui Kohama, Nobuyuki Tsuboi, Kouhei Ozawa, Koichi A Hayashi

29th International Colloquium on the Dynamics of Explosions and Reactive Systems Papaer 176 2023年07月

Analysis on Pressure Gain of Rotating Detonation Engine 査読有り国際誌

A. K. Hayashi, Y. Otsuka, K. Ishii, K. Yoshidomi, T. Ito, N. Tsuboi, K. Ozawa

The 34th International Symposium on Shock Waves T04-0282 2023年07月

Effects of Reynolds Number and Ramp Angle on Gortler Vortices over a Compression Ramp 査読有り国際誌

Kalash Dixit, Ritu Raj Kumar, Nagabhushana Rao Vadlamani, Nobuyuki Tsuboi

The 34th International Symposium on Shock Waves T19-0135 2023年07月

Numerical Simulation on DDT in Real and Large Scale Combustion Chamber Using a Combustion Velocity Model and Ignition Model with a Detailed Chemical Reaction System 査読有り

Ichiro Nakamori, Takayuki Tomizuka, Atsuo Takahashi, Fumitomo Onishi, Mikhail Kuznetsov, Takashi Kodama, Yoshikazu Tamauchi, Naoya Sato, A. Koichi Hayashi and Nobuyuki Tsuboi

29th International Colloquium on the Dynamics of Explosions and Reactive Systems Paper 127 2023年07月

Detailed Numerical Simulation on Dimethyl Ether/Oxygen Premixture Detonation Using Reduced Chemical Reaction Model -Disturbance of Cellular Structure- 査読有り国際誌

Kubota Daiki, Tsuboi Nobuyuki, Ozawa Kohei, Hahashi A. Koichi

29th International Colloquium on the Dynamics of Explosions and Reactive Systems Paper 193 2023年07月

Operation characteristics of a disk-type rotating detonation engine 査読有り国際誌

Ishii K., Ohno K., Kawana H., Kawasaki K., Hayashi A.K., Tsuboi N.

Shock Waves 33 ( 3 ) 267 - 274 2023年04月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

In the present work, operation characteristics of a disk-type rotating detonation engine (DRDE) with a constant chamber area were experimentally studied for various total mass flow rates and a wide variety of equivalence ratios of hydrogen–air mixtures. From the direct visualizations, the rotating detonation wave was found to propagate near the outer wall of the combustion chamber, regardless of the wave mode. For the present test conditions, single- and double-wave modes are observed, depending on the equivalence ratio of the mixture. The pressure gain was evaluated based on a one-dimensional flow model together with the chamber static pressure measured with the capillary tube average pressure technique. Although the present DRDE configuration provided a negative pressure gain for all the test conditions, it was found that the single-wave mode was superior to the double-wave mode in terms of the pressure gain.

DOI： 10.1007/s00193-023-01133-6

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Influence of tube cross-section geometry on high-pressure hydrogen-flow-induced self-ignition 査読有り国際誌

Asahara M., Yokoyama A., Tsuboi N., Hayashi A.K.

International Journal of Hydrogen Energy 48 ( 21 ) 7909 - 7926 2023年03月

記述言語：英語掲載種別：研究論文（学術雑誌）

Self-ignition within a cylindrical tube that discharges high-pressure hydrogen results in flame formation. Because rectangular tubes are used to visualize fuel-flow dynamics, the influence of the tube cross-section on the self-ignition characteristics is investigated. As experimental investigation of the mechanisms underlying the self-ignition phenomenon in cylindrical tubes is difficult, three-dimensional numerical simulation is employed. Following the bursting of diaphragm by high-pressure hydrogen with a storage pressure of 9.0 MPa and a temperature of 300 K, initial self-ignition occurs at the center of the rectangular tube sidewall. This is because of the mixing of air and hydrogen induced by the bow-shock reflection-generated jet flow and resulting adiabatic shock compression-induced temperature increase. This temperature rise induces a secondary self-ignition at the tube corners. In the cylindrical tube, a solitary ring-shaped self-ignition occurs near the sidewall. The flame evolutions in rectangular and cylindrical tubes reveal similar flame-spreading trends, which indicates similar bow-shock reflection-induced self-ignition mechanisms.

DOI： 10.1016/j.ijhydene.2022.08.210

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Numerical Study of Cryogenic Hydrogen Jet in Crossflow under Supercritical Pressure: Comparison of Tandem and Twin Jets 査読有り国際誌

NAKATSUKASA Tomohito, AMANO Taishi, ARAKI Takahide, TERASHIMA Hiroshi, TSUBOI Nobuyuki, OZAWA Kohei

Journal of Evolving Space Activities ( 宇宙技術および科学の国際シンポジウム ) 1 ( 0 ) n/a 2023年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

The present study numerically investigates the flow fields of the twin- and tandem-jet in crossflow (JIC) under supercritical pressure. An ILES/RANS method is applied. In the present JIC, cryogenic hydrogen jets are vertically injected to warm temperature hydrogen crossflow through circular injector holes. The results show that the penetration of cryogenic jets into the crossflow is more enhanced with the tandem-jet than with the twin-jet. The higher jet penetration with the tandem jets is caused by a downstream jet behavior less influenced by the crossflow. Nevertheless, a mixedness analysis indicates that the mixing state at a downstream position is almost similar between the tandem and twin jets.

DOI： 10.57350/jesa.29

CiNii Research

Visualization of the physical destruction process of additive-manufactured regression sensor structures 査読有り国際誌

Ozawa Kohei, Neki Tomoya, Tsuboi Nobuyuki

Science and Technology of Energetic Materials ( 一般社団法人火薬学会 ) 84 ( 2 ) 24 - 31 2023年01月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

Advanced closed-loop control of thrust and mixture ratio of hybrid rockets can be realized by combing a fuel mass flow rate control technique with a real-time fuel regression measurement. One of the promising techniques to realize real-time fuel regression measurement is the multi-material-additive-manufactured solid fuel with an integrated sensor probe structure. In this work, the destruction process of its regression sensor structure was visualized by the high-speed video from the top view of the sensor structure. The acquired high-speed video revealed the destruction process and its relationship with the time history of the voltage on the sensor structure. One of the findings is that unevenness or bumps of the rung form hot spots with strong emission, leading to the dropping-off and entrainment of the fragmented rung into the diffusion flame. Another important finding is that the destruction process of the rung starts before the rapid voltage increase, but it precedes the more intensive and frequent destruction. The post-processing of the sequential frames of the high-speed video successfully provided the observation of the fuel surface behind the diffusion flames. These reconstructed videos visualized the motions of the fragmented rung remaining on the fuel surface. The physical destruction process of the regression sensor structure revealed in this study can contribute to the improvement of the sensor structure design to avoid the unexpected off-nominal responses previously observed.

DOI： 10.34571/stem.84.2_24

CiNii Research

Validation of Soave–Redlich–Kwong equation of state coupled with a classical mixing rule for sound speed of non-ideal gas mixture of oxygen-hydrogen as liquid rocket propellants 査読有り国際誌

Takahashi R., Tsuboi N., Tokumasu T., Tsuda S.I.

Journal of Thermal Science and Technology ( 一般社団法人日本機械学会・社団法人日本伝熱学会 ) 18 ( 1 ) 22-00365 - 22-00365 2023年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

Numerical simulations of inlet jets flow of propellants in the main combustion chamber equipped in a liquid rocket engine have been conducted by compressible CFD technics employing a van der Waals-type equation of state (EOS) and chemical reaction models. Various simulations have been already conducted both for combustion and non-combustion state in the chamber; however, the accuracy of EOS for the mixture of propellant employing a classical mixing rule (CMR), particularly for the sound speed, has not been understood well. Therefore, we have validated the applicability of Soave–Redlich–Kwong (SRK) EOS as one of the van der Waals-type EOSs coupled with the CMR for the sound speed using molecular dynamics (MD) simulations against an imaginary model of oxygen-hydrogen mixture system. We found that SRK EOS coupled with a well-employed CMR can reproduce the sound speed in the MD simulations within a relative error of several percent and that the CMR hardly increases the deviation of the SRK EOS in the single component. The present results suggest that the SRK EOS with the CMR cannot be the main factor to cause critical errors in the CFD based on RANS, which will give reliability to current CFD simulations for internal flows in a combustion chamber of a liquid rocket engine.

DOI： 10.1299/jtst.22-00365

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CiNii Research

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3D Evaluation of Premixed Gas Injection Ports Number on Flow Field in Disk RDE 査読有り国際誌

Ito T., Tsuboi N., Ozawa K., Hayashi A.K.

AIAA SciTech Forum and Exposition, 2023 2023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）

Three-dimensional viscous simulations on the DRDE (disk-type rotating detonation engine) are presented using the Navier-Stokes equations with the H2-air UT-JAXA reaction mechanism. The purposes of this study are to visualize the propagation pattern inside the DRDE combustor, to investigate the number of injection ports on the propagation pattern, and to evaluate their effects on the stable propagation of detonation and the performance of the DRDE. The results show that the number of injection ports affects the generation of new detonation waves; that the number of injection ports is related to the number of propagating detonation waves; that when two detonation waves are propagating, they have a characteristic form of propagation that they approach and leave each other.

DOI： 10.2514/6.2023-0577

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Numerical Study on Pressure Gain of Rotating Detonation System 査読有り国際誌

Koichi Hayashi A., Ito T., Tsuboi N., Ozawa K., Ishii K., Dzieminska E., Obara T., Maeda S., Mizukaki T.

AIAA SciTech Forum and Exposition, 2023 2023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）

The study of pressure gain (PG) for disc type - rotating detonation engine (D-RDE) is performed numerically to figure out how their PG can be increased. The mixture system of H2/O2 is applied to see a difference in PG between two different dimension calculation. The numerical system is performed using the 2D- and 3D- compressible Navier-Stokes equations with the UT-JAXA hydrogen combustion mechanism. The experimental data from H2/air mixture for PG are also obtained to compare with the previously obtained numerical data. The present numerical results show that the PG of D-RDE is almost no difference or a bit smaller than that of regular RDE. To get an increase of PG, the relation between injection pressure and exit pressure of chamber, P8/P3,1, we have to check the area ratio between the fuel injection total area and the exit area, the effect of mass flow rate on PG, and the back pressure effect on PG.

DOI： 10.2514/6.2023-2565

Kyutacar

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Numerical study on unsteady characteristics of high-pressure hydrogen jet ejected from a pinhole 査読有り

Asahara M., Iwasa T., Tsuboi N., Hayashi A.K.

International Journal of Hydrogen Energy 47 ( 74 ) 31709 - 31728 2022年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

The aim of this study was to delineate the unsteady fluid dynamics of the high-pressure hydrogen jet to clarify the relationship between the forced ignition position and the flame development characteristics in a high-pressure hydrogen jet leaking from a pinhole. The Navier–Stokes equation for a compressible multi-component gas was used to simulate a high-pressure (82 MPa stagnation pressure) unsteady hydrogen jet ejected into the atmosphere through a pinhole (diameter = 0.2 mm). The results indicated that the flapping jet at the base of the jet formed a cloud of highly concentrated hydrogen that flowed downstream. A correlation was observed between the spatio-temporal distribution of hydrogen concentration and velocity was observed. The unsteady high-pressure hydrogen jet obtained by simulation will be used in subsequent studies focusing on flame development under forced ignition.

DOI： 10.1016/j.ijhydene.2022.05.079

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