Hysteretic Phenomenon of Shock Wave in a Supersonic Nozzle

In recent years, hysteretic phenomena in fluid flow systems drew attention for their great variety of industrial and engineering applications. When the high-pressure gas is exhausted to atmosphere from the nozzle exit, the expanded supersonic jet with the Mach disk is formed at a specific condition. In two-dimensional expanded supersonic jet, the hysteresis phenomenon for the reflection type of shock wave is occurred under the quasi-steady flow and the transitional pressure ratio between the regular reflection and Mach reflection is affected by this phe- nomenon. However, so far, there are very few researches for the hysteretic phenomenon of shock wave in a supersonic internal flow and the phenomenon has not been investigated satisfactorily. The present study was concemed with the experimental and numerical investigations of hysteretic phenomena of shock wave in a supersonic nozzle, and discussed the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time.     

Configuration of Shock Waves in Two-Dimensional Overexpanded Jets

An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio pe/pb of the nozzle exit pressure pe to the back pressure pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio pe/pb, even if the pe/pb is under overexpanded conditions.     

Shock wave in supersonic moist air jet for a low pressure ratio

In the present study,a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet.The unsteady,compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study.The numerical simulations have been performed for low pressure ratio and various humidities.The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur,depending on humidity of the air.     

Transient supersonic release of hydrogen from a high pressure vessel: A computational analysis

Understanding the characteristics of a hydrogen gas jet exiting from a compressed vessel during vessel rupture or venting is crucial for determining safety requirements for distribution and use of hydrogen. Such jets can undergo several flow regimes during venting, from initial supersonic flow, to transonic, to subsonic flow regimes as the pressure in the vessel decreases. A bow shock wave is a characteristic flow structure during the initial stage of the jet development, and this paper focuses on the development of the bow shock wave and the jet structure behind it. The transient behaviour of an impulsively initiated jet is investigated using unsteady, compressible flow simulations. Both the cases of a hydrogen jet exiting into quiescent hydrogen and of a hydrogen jet exiting into air are presented. The gases are considered to be ideal, and the computational domain is axisymmetric. The jet structure, including the shock wave and flow separation due to an adverse pressure gradient at the nozzle is investigated with a focus on the differences between the single- and multi-component flow scenarios.     

Passive control of unsteady condensation shock wave

IntroductionIn the case of moist air or steam rapidly expanding ina supersonic nozzle, nollequilibrium condensation occursin the flow field and the flow will be affected by thelatent heat leleased by condensationll-4]. Thereby, if theheat exceeds a certain quantity, the flow will becomeunstable and oscillations of a periodic flow occurs[5-91. Forthe unsteady condensation shock wave, it is blown thatthere are three types of oscillationslg]. These types aredescribed below:1. Mode l: A condensat…     

Characteristics of the Mach Disk in the Underexpanded Jet in which the Back Pressure Continuously Changes with Time

When the high-pressure gas is exhausted to the vacuum chamber from the nozzle, the underexpanded supersonic jet contained with the Mach disk is generally formed. The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time. The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper. The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation. The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.     

Effects of cavity-induced mixing enhancement under oblique shock wave interference: Numerical study

In this research, the effects of oblique shock on the mixing characteristics in a supersonic combustor equipped with a cavity is numerically investigated. To reveal the flow structure of the supersonic flow field under oblique shock wave interference, three-dimensional steady RANS equations and SST k-ω turbulence model are adopted. The current work focuses on comparing the interaction effects between oblique shock wave and bow shock wave, which are formed by fuel jet on fuel mixing under different conditions. The numerical analysis demonstrates that an optimal angle exists for the mixing efficiency of the ramp. The optimal angle diminishes as the jet-to-crossflow pressure ratio increases. The oblique shock wave in a certain range is conducive to enhance the penetration depth of ethylene. The smaller angle of the ramp does not cause large stagnation pressure losses.     

Self—Induced Oscillation of Supersonic Jet During Impingement on Cylindrical Body

INTaoDUCTIONThephenomenaoftheinteractionbetweenthesu-personicjetandanobstaclearerelatedtotheproblemSoftheaeronauticalengineeringsuchasthedesignoftherocketlaunchersysteml1]andillterestinginrela-tiontotheindustrialengineerings.Thefiowisshowntobethehsocomplexthreedimensionalwavpat-terncolit~shodwavesduetotheimpingemelltofasuPersonicjetonanobstacle,ManystudiesontheinteractionbrtweenthesuPersonicjetandanobstaclehavebeenreportedconcerningtheinteractionsoftheshodwaves[l]-I5l,theflowcharacteristi…     

Effects of incident shock wave on mixing and flame holding of hydrogen in supersonic air flow

The effects of incident shock wave on mixing and flame holding of hydrogen in supersonic airflow have been studied numerically. The considered flow field was including of a sonic transverse hydrogen jet injected in a supersonic air stream. Under-expanded hydrogen jet was injected from a slot injector. Flow structure and fuel/air mixing mechanism were investigated numerically. Three-dimensional Navier–Stokes equations were solved along with SST k-ω turbulence model using OpenFOAM CFD toolbox. Impact of intersection point of incident shock and fuel jet on the flame stability was studied. According to the results, without oblique shock, mixing occurs at a low rate. When the intersection of incident shock and the lower surface is at upstream of the injection slot; no significant change occurs in the structure of the flow field at downstream. However when the intersection moves toward downstream of injection slot; dimensions of the recirculation zone and hydrogen-air mixing rate increase simultaneously. Consequently, an enhanced mixing zone occurs downstream of the injection slot which leads to flame-holding.     

圆湍射流的轴对称大涡模拟

对空间发展的不可压缩圆湍射流进行了大涡模拟研究。在流动轴对称假定下,对Re数等于11300的圆浩射流流动进行数值模拟。大涡模拟很好地再现了圆湍射流中拟序结构非定常演化的前期过程,成功地捕获到了射流中Kelvin～Helmholtz不稳定性的触发与初级涡环的卷起及其第一次和第二次配对合并现象。但在流动轴对称假设下,大涡模拟不能模拟出湍流拟序涡环结构的破碎过程。对圆湍射流的轴对称大涡模拟结果进行长时间统计平均,能够预报出圆湍射流的核心区特征,但与圆湍射流的理论分析解和经典的实验数据对比发现,核心区后大涡模拟预报的流向速度降低缓慢。从控制方程的数学本质和拟序结构的物理机制上对圆湍射流在轴对称假设下产生上述大涡模拟结果的原因进行了分析与探讨。     

激波风洞中超声速燃烧现象的初步实验研究

激波风洞可以提供超声速燃烧现象研究需要的高速和高温实验模拟条件,而且在实验时间上优于膨胀管和重活塞风洞,但是由于其技术难度,很少用于超声速燃烧现象研究。文章介绍了启用激波风洞进行燃烧研究所作的改造和得到的初步实验结果。实验除测量常规流场参数和模型表面的动态参数外,主要使用二维实验模型,利用高温气体的自发光和燃烧伴随的发光现象,采用高速摄影技术来观测燃烧现象,记录到高焓流场中叠加燃料喷射和燃烧的流场,观察到自由边界条件下扩控制的超声速燃烧现象。结果表明激波风洞用于超声速燃烧研究的一些必要的技术问题已基本解决。     

Unsteady shock-flow characteristics in an over-expanded rocket nozzle

<正>A numerical investigation of transient side-loads in an axisymmetric over-expanded thrust optimized contour nozzle is presented.These nozzles experience side-loads during start-up and shut-down operations,because of the flow separation at nozzle walls.Two types of flow separations such as FSS and RSS shock structure occur.A two-dimension numerical simulation has been carried out over an axisymmetric TOC nozzle to validate present results and investigate oscillatory flow characteristics for start-up processes.Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme.Governing equations are solved by coupled implicit scheme.Reynolds Stress turbulence model is selected.Present computed pressure at the nozzle wall closely matched with experiment data.A hysteresis phenomenon has been observed between these two shock structures.The transition from FSS to RSS pattern during start-up process has shown maximum nozzle wall pressure.Nozzle wall pressure and shear stress values have shown fluctuations during the FSS to RSS transition. The oscillatory pressure has been observed on the nozzle wall for high pressure ratio.Present results have shown that magnitude of the nozzle wall pressure variation is high for the oscillatory phenomenon.     

A Study of Under-expanded Moist Air Jet Impinging on a Flat Plate

When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is under-expanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with non-equilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics are not known satisfactorily. In the present study, the effect of the non-equilibrium condensation on the under-expanded air jet impinging on a vertical flat plate is investigated numerically in the case with non-equilibrium condensation, frequency of oscillation for the flow field becomes larger than that without the non-equilibrium condensation, and amplitudes of static pressure become small compared with those of dry air. Furthermore, the numerical results are compared with experimental ones.     

The initiation and propagation of detonation in supersonic combustible flow with boundary layer

Adaptive simulations solving the Navier-Stokes equations have been conducted in order to get a better understanding on the detonation initiation and propagation in a stoichiometric H₂/O₂/Ar supersonic mixture with boundary layer. The detonation is initiated by a continuous hot jet. When reflecting on the wall, the jet induced bow shock interacts with the boundary layer and forms the shock boundary layer interaction phenomena, while in Euler result the bow shock forms Mach reflection. The investigation shows that the Navier-Stokes simulation result is structurally in better agreement with the experiment compared with that of the inviscid Euler simulation result. The bow shock interacts with the separation shock, forming the shock induced combustion behind the interaction zone. Then the combustion front couples with shock and forms Mach stem induced detonation. The Mach stem induced detonation continues to getting higher and propagating upstream, initiating the main flow. The initiated partial detonation exists with the separation shock induced combustion front, forming an “oblique shock induced combustion-partial detonation” structure in the main flow. The investigation on the influence of free stream Mach number further confirms that the boundary layer has an important influence on detonation initiation. The parametric studies also show that there exists a free stream Mach number range to initiate the partial detonation in supersonic combustible flow successfully.     

Study on Transonic Tone in an Axisymmetric Supersonic Nozzle

This paper describes experimental and numerical works to investigate noise phenomenon in supersonic flow dis- charged from a convergent-divergent nozzle. The noise phenomenon of flow is generated by an emission of ＇transonic tones＇. The results obtained show that the frequency of a transonic tone, that differs from the frequency of a screech tone due to the shock-cell structures in a jet and originates in the shock wave in the nozzle, increases in proportion to the nozzle pressure ratio. The high-order transonic tone has the directivity in the direction of the flow. As for the transonic tone＇s frequency, the separated zone was calculated by using a simple flow model con- sidering the propagating perturbation. The results of the model corresponded to the results of this experiment well.     

Passive Control of Transonic Flow Fields with Shock Wave Using Non—equilibrium Condensation and Porous wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.     

Mechanism of spontaneous ignition of high-pressure hydrogen during its release through a tube with local contraction: A numerical study

The tendency of spontaneous ignition of high-pressure hydrogen during its sudden release into a tube is one of the main threats to the safe application of hydrogen energy. A series of investigations have shown that the tube structure is a key factor affecting the spontaneous ignition of high-pressure hydrogen. In this paper, a numerical study is conducted to reveal the mechanism of spontaneous ignition of high-pressure hydrogen inside the tube with local contraction. Large Eddy Simulation, Renormalization Group, Eddy Dissipation Concept, 37-step detailed hydrogen combustion mechanism and 10-step like opening process of burst disk are employed. Three cases with burst pressures of 3.10, 4.90, and 8.45 MPa are simulated to compare against the pervious experimental study. The spontaneous conditions and positions agree well with the experimental results. The numerical results indicate that shock wave reflection takes place at the upstream vertical wall of contraction part. The interacted-shock-affected region is generated at the tube center because of the subsequent shock wave interaction. The forward reflected shock wave couples with normal shock wave and increases the pressure of leading shock wave. The sudden contraction of tube blocks the propagation of hydrogen jet and decreases the speed from supersonic flow to subsonic flow. More flammable mixture is generated inside the contraction part, as a results, the length of the flame is increased. Two mechanisms are proposed finally.     

Two-dimensional numerical simulations of shock waves in micro convergent–divergent nozzles

The steady two-dimensional Navier–Stokes equations with the slip wall boundary conditions were used to simulate the supersonic flow in micro convergent–divergent nozzles. It is observed that shock waves can take place inside or outside of the micronozzles under the earth environment. For the over-expanded flows, there is a boundary layer separation point, downstream of which a wave interface separates the viscous boundary layer with back air flow and the inviscid core flow. The oblique shock wave is followed by the bow shock and shock diamond. The viscous boundary layer thickness relative to the whole nozzle width on the exit plane is increased but attains the maximum value around of 0.5 and oscillates against this value with the continuous increasing of the nozzle upstream pressures. The viscous effect either changes the normal shock waves outside of the nozzle for the inviscid flow to the oblique shock waves inside the nozzle, or transfers the expansion jet flow without shock waves for the inviscid flow to the oblique shock waves outside of the nozzle.     

Effect of Axisymmetric Sonic Nozzle Geometry on Characteristics of Supersonic Air Jet

The effect of nozzle geometry on sonic line and characteristics of supersonic air jet was studied. Computational fluid dynamics was applied in this study. The axisymmetric nozzle geometries investigated were two different contour converging nozzles, two different conically converging sharp-edged nozzles and a sharp-edged orifice. The results show that the supersonic jet structure, sonic line and streamlines in supersonic jet are strongly influenced by the nozzle geometry, and the total pressure loss increases with the increase of Mach disk diameter. The present numerical simulation is an effective tool to evaluate compressible flows in supersonic air jet.     

Passive Control of Steady Condensation Shock Wave

IntroductionA rapid expansion of moist air or steam in asupersonic nozzle gives rise to nonequilibriumcondensation phenomena. Thereby, the nozzle flow isaffected by the latent heat released by condensation ofwater vapouf, and if the heat released exceeds a certainquantity, a condensation shock wave will occur[1-4].Many works for the passive contfol of shockboundary layer interaction using the porous wall with aplenum underneath have been repofted on the applicationof the technique tO tfansonic…