著者

小原 哲郎 大八木 重治 高藤 亮一 蔡 品

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 B編 (ISSN:03875016)

巻号頁・発行日

vol.67, no.659, pp.1680-1686, 2001-07-25 (Released:2008-03-28)

参考文献数

14

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Experiments are carried out to investigate behavior of shock wave diffraction from a safety-engineering point of view. Because, once the shock wave is released into an ambience, high pressure and negative pressure lasting for relatively long period have possibility to cause serious damages against human bodies as well as general buildings. Therefore, it should be one of the most significant subjects to attenuate the shock wave efficiently within a short distance from the source. In this report, a cavity is installed at an open end of a shock tube and flow-fields behind diffracted shock wave are visualized using schlieren photography. In addition, piezo-electric pressure transducer is flush mounted on the surface of reflector, which is installed at test section, and pressure histories are recorded with wide frequency response. Lastly, numerical simulation using the TVD finite difference scheme is performed to compare with the experimental results. As a result, (i) the pressure histories on the reflector coincides well between the numerical and experimental results, (ii) flow-fields behind the shock wave are clarified, (iii) maximum pressure behind reflected shock wave can be attenuated by installing several cavities inside the open end of the shock tube.

著者

高藤 亮一 山中 昭央 小原 哲郎 蔡 品 大八木 重治

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 B編 (ISSN:03875016)

巻号頁・発行日

vol.65, no.639, pp.3602-3607, 1999-11-25 (Released:2008-03-28)

参考文献数

12

被引用文献数

2 2

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As is well known when a shock wave is emitted from an open end of a tube, an expansion wave and a vortex ring are generated behind the shock wave. Furthermore, a contact surface, slip line and these wave interactions may cause considerably complicate flow-fields. In this study, shock waves of Mach number 1.3, 1.6 and 2.2 are produced utilizing diaphragm-less shock tube of 50 mm diameter and c. a. 10 m total length, and the flow-fields are visualized with an aid of schlieren optical techniques. A cylindrical reflector is installed at test section and stagnation pressure behind reflected shock wave is measured with wide frequency response. A numerical analysis is also carried out to investigate these flow-fields using Predictor-Corrector TVD finite difference scheme. As a result, (i) the contour of diffracted shock wave is well coincided between experimental and numerical results, (ii) pressure histories behind reflected shock wave are clarified, (iii) an empirical formula is obtained between Mach number, non-dimensional distance from the open end of the tube and non-dimensional pressure just behind reflected shock wave.

著者

前田 慎市 倉持 悠希 小野 涼 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.850, pp.17-00049-17-00049, 2017 (Released:2017-06-25)

参考文献数

21

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This study addressed a deflagration-to-detonation transition (DDT) process after interaction of the convex flame with a planar shock wave. High-speedvideo cameras and schlieren optical technique were utilized to observe the DDT as well as shock-flame interaction processes. A double-diaphragmshock tube was used to produce the shock wave, while the flame was produced by igniting a premixed gas of stoichiometric methane-oxygenat the observation section. Experiments were conducted by changing Mach number of the incident shock wave, Ms and a distance of flame front from the end wall, x0. As a result of schlieren photographs, flame propagation behaviors at initial stage were classified into four patterns, named as (a) coupling, (b) concave, (c) partial coupling and (d) convex type. The propagation patterns of flame were highly dependent on the initial position of flame front, x0. Under the experimental conditions, DDT was not observed when the flame had been propagated revealing (a) coupling (observed with the conditions of x0 > 110 mm) and (d) convex type (x0 < 50 mm). However, the DDT was observed following that the flame had been propagated revealing (b) concave or (c) partial coupling (50 < x0 < 110 mm). Furthermore, it was elucidated that DDT was typically caused through the following processes. (i) When the convex flame interacted with planar shock, the unburned gas was penetrated into burned gas inducing Richtmyer-Meshkov instability. (ii) The flame was highly accelerated at boundary layers behind the reflected shock. (iii) After accelerated flame propagated through the unburned shocked region, local explosion was occurred on the wall followed by detonation onset.

著者

永井 厚司 岡部 俊彦 キム ギョンミン 吉橋 照夫 小原 哲郎 大八木 重治

出版者

一般社団法人 日本燃焼学会

雑誌

日本燃焼学会誌 = Journal of the Combustion Society of Japan (ISSN:13471864)

巻号頁・発行日

vol.52, no.159, pp.86-93, 2010-02-15

参考文献数

27

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<p>Pulse detonation engines (PDEs) are expected to be the next-generation engine systems, and are expected to have applications in various fields. One of the fundamental problems faced during the development of PDEs is the deflagration to detonation transition (DDT). In order to realize a PDE, it is essential to shorten a parameter of detonation transition called a detonation induction distance (DID). However, the mechanism underlying the DDT process and methods to shorten DID in narrow channels have not yet been understood. An experimental study on DDT process in a narrow rectangular channel with a height of 1-5 mm and a width of 8 mm was carried out by employing pressure transducers, ionization probes, and sooted plate technique in oxyhydrogen mixtures. The effects of the tube height and equivalence ratio on pressure detonation limits were discussed. Detonation velocity, DDT process, and DID were discussed on the basis of pressure history and soot track record. Overdriven detonation and attenuated detonation were observed in the narrow channel. The DID value measured on the basis of the soot track record in the present study was in the range of the empirical formula obtained by the other researchers.</p>

著者

前田 慎市 吉木 一秀 菅野 祥一郎 冨田 啓太 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.17-00019-17-00019, 2017 (Released:2017-08-25)

参考文献数

26

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Shock-induced combustion around a spherical body was experimentally investigated by launching the projectile at supersonic speed into a combustible mixture. This study focused on occurrence conditions for an unsteady combustion which was characterized as combustion instabilities with an oscillating combustion front. A spherical body of 4.76 mm dimeter was used as the projectile, and its flight Mach numbers were ranged from 3.5 to 7.5. Four types of combustible mixtures, which were stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures diluted with argon or nitrogen (2H2 + O2 + 3Ar, 2H2 + O2 + N2, C2H4 + 3O2 + 12Ar, C2H4 + 3O2 + 2.5N2), were used and their initial pressures were varied between 25 and 100 kPa. The combustion regimes around the projectile were observed by using a schlieren optical system and high-speed camera. The combustion regimes generally varied from the steady combustion with smooth combustion front to the unsteady combustion with oscillating combustion front, when the projectile Mach number or the initial pressure increased. The occurrence conditions for the unsteady combustion were expressed by the two dimensionless parameters; dimensionless heat release rate, q*t* and dimensionless induction length, lind*, which were defined by the post-shock state and flow velocity on the stagnation streamline of the projectile and by assuming the chemical reaction as a constant-volume explosion. The q*t* included a temperature gradient in a reaction zone, and represented the strength of the pressure wave driven by the heat release reaction. The lind* included an induction time, and represented the distance between the shock wave and the location where the heat release reaction started. The unsteady combustion occurred when these two dimensionless parameters were above the critical values, and the trend of occurrence condition of the two combustion regimes could be explained by introducing the parameters.

著者

前田 慎市 及川 陽介 星野 隆介 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.17-00039-17-00039, 2017 (Released:2017-08-25)

参考文献数

10

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A detonation wave propagating in a straight tube (detonation tube) was reflected off the end wall of the tube, and the pressure profile produced by the propagation of the reflected shock wave was experimentally investigated. The detonation wave was initiated at the opposite end of the reflection end, and two ignition conditions were tested. First, ignition at the closed end of the tube (called as “closed ignition end condition”), where the fluid motion was negligible, was evaluated. Second, ignition at the open end of the tube (called as “opened ignition end condition”), where the burned gas flowed toward the vacuum tank attached to the detonation tube, was evaluated. Karnesky et al. (2013) suggested the empirical model in order to represent the pressure profile near the reflection end in the closed ignition end condition. In this paper, the empirical model of Karnesky et al. was modified in order to represent the pressure profile in the opened ignition end condition, and the effect of two ignition conditions on the pressure profiles was discussed. In these models, the pressure profile at the reflection end was empirically formulated by using two empirical parameters, and a uniform pressure distribution between the reflected shock wave and the reflection end was assumed. In this paper, the empirical parameters were normalized by the characteristic parameters for the propagating reflected shock wave. These parameters expressed the conditions of the combustible mixture and the length of the detonation tube. In the opened ignition end condition, the model well represented the measured pressure profile created by the propagating detonation wave and reflected shock wave in the entire length of the detonation tube because the rarefaction wave existed in the entire region behind the detonation wave, and the pressure behind the reflected shock wave had an approximately uniform distribution. Conversely, the model was applicable for a limited duration for the closed ignition end condition because a pressure gradient gradually developed behind the reflected shock wave when the reflected shock wave began to propagate in the plateau region behind the rarefaction wave.

著者

前田 慎市 青島 亮太 黒澤 哲朗 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.846, pp.16-00269-16-00269, 2017 (Released:2017-02-25)

参考文献数

20

被引用文献数

1

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Detonation transition was experimentally investigated using flame jetting through the orifice of a small sub-chamber, which was equipped on the side wall near the closed end of the main channel (square inner closs section, 50 mm on a side) filled with a stoichiometric hydrogen-oxygen mixture at an initial pressure of 80 kPa. The number of sub-chambers and orifice diameters were changed as 1, 2, 4 (called as FJ1, FJ2, FJ4, respectively) and 3, 5, 7 mm, respectively, and the facing flame jets were collided with each other in FJ2 and FJ4. Two regimes of detonation transition were observed: (i) deflagration-to-detonation transition (DDT) accompanied by flame acceleration process and (ii) direction initiation of a detonation near the flame jetting section. The flame propagation distance required for detonation transition was one-half to one-third for regime (i) compared to single-spark ignition without flame jet, and below one-sixth for regime (ii). Except for the case of regime (ii), observed for an orifice diameter of 5 or 7 mm of FJ4, the detonation transition distance had no significant effect on the types of flame jetting and orifice diameters. Time-resolved schlieren recordings showed that the choked jet of combustion products drove the shock wave preceding the flame front, and induced multi-dimensional flame motion and repeated shock-flame interactions in the confinement. These behaviors enhanced flame velocity at the ignition end by a factor of 4 to 7 in FJ1 and FJ2, compared to single-spark ignition. The effect of these enhanced flame velocities on DDT distances was consistent with the semi-empirical model of flame acceleration process in a smooth tube. The schlieren recordings and pressure measurements at the closed end indicated that the possible factors for the initiation of detonation in regime (ii) were the mixing of reacted and unreacted gas induced by the repeated strong shock-flame interaction and the hot spot formed by shock-shock interaction driven by the facing flame jetting.

著者

前田 慎市 菅野 祥一郎 古藤 亮平 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

pp.14-00332, (Released:2015-01-16)

参考文献数

26

被引用文献数

1

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The gaseous detonation driven gas gun was developed for accelerating the projectile to a supersonic speed. The gas gun was simply consisted of two straight stainless-steel tubes. The one was the detonation tube and the other was the launch tube. The detonation tube was 50 mm inside diameter with 2180 or 4280 mm long, and the launch tube was 5 mm inside diameter with 1040 mm long. Chapman-Jouguet detonation wave was initiated in the detonation tube, and the projectile was accelerated in the launch tube via combustion products behind the detonation wave. The spherical projectile of 4.76 mm diameter was made of high-density polyethylene with 52 mg mass. The driver mixture was stoichiometric hydrogen-oxygen premixed gas with initial pressure ranging from 120 to 450 kPa. The gas gun was successfully operated, and the maximum projectile velocity of 1400 m/s was obtained for the conditions that the detonation tube was 4280 mm long and the initial pressure of the driver gas was 450 kPa. The results of the longer detonation tube demonstrated that the projectile velocity was 1.15 - 1.25 times higher than the case of shorter detonation tube. This velocity change of the projectile could be explained by the pressure increase at the inlet of the launch tube by using longer detonation tube. The reason of the pressure increase has a possibility that the length of Taylor wave behind the detonation wave becomes longer for the case of longer detonation tube.

著者

小原 哲郎

出版者

埼玉大学

雑誌

若手研究(B)

巻号頁・発行日

2001

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パルスデトネーションエンジン(PDE)は,これまでのジェットエンジンの構造と大きく異なる.すなわち,PDEではエンジン筒内に燃料と酸化剤をパルス状に噴射させて,混合気を着火しデトネーション波を発生させ既燃気体をノズルによって噴射し推力を得るのが基本原理である.しかしながら,PDEはまだ構想あるいは試験段階にあり,実用化するには至っていない.そこで,申請者はPDEの開発に必要な基礎データを得ることを研究目的とし,本研究課題を遂行した.まず,研究の初年度において,PDEの試作機を構築し,実験を開始した.本年度においては系統的に実験を進め,主に以下の知見が得られた.(1)本装置におけるデフラグレーション波からデトネーション波への遷移過程(DDT過程)では,混合気の点火位置を管端より下流の側壁上で行うことで上流と下流へ伝ぱする2つのデトネーション波を生成し,特にスラスト壁付近で生じる過大デトネーションは点火位置から非常に短距離で生じることを明らかにした.(2)筒内に噴射するした際の混合気の初期圧力や当量比の影響について調べ,燃焼後の圧力変化について明らかにした.また,量論混合比においてDDT過程への短縮効果が大きいことを明らかにした.(3)本装置により作動周波数50Hzまでのパルス作動が可能なことを明らかにした.また,得られる比推力は作動周波数によらず一定となること,すなわち推力がサイクル速度に比例して増加することを明らかにした.(4)エンジン筒内に挿入する内部障害物はデトネーション波の伝ぱ持続性を高め比推力が増加すること,また管の長さの増加はノズルのように作用し比推力を増加できることが明らかとなった.