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1.
为了了解超燃冲压发动机中三维斜激波与壁面的相交情况,以冷态模拟为基础,对两种不同形状的斜劈结构产生的斜激波进行数值模拟。当斜劈展向与气流方向成45.0°时,激波和膨胀波结构呈现三维特性,并且激波在两侧壁面处的反射现象不同。以激波面上游为视角,当激波与壁面相交成锐角时会产生马赫反射;而激波与壁面相交成钝角则会以叠加膨胀波的形式减弱激波,并且使激波面的法线方向与壁面的法线方向垂直。由于两侧壁面的影响,随着高度的增加激波强度减弱,同时气体经过斜激波后偏转角度也减小。对于构型Ⅱ,有斜劈的区域产生三维斜激波会延伸到无斜劈区域,此时下壁面与斜激波相交成钝角,同样会以叠加膨胀波的形式减弱斜激波。  相似文献   

2.
    
Rotating detonation as a kind of pressure gain combustion is expected to greatly improve efficiency when applied to gas turbine engines. In this paper, the operation of rotating detonation combustor and turbine rotor blade was studied. Firstly, the analysis of the interaction between detonation wave and turbine blade shows that the compression of gas by detonation wave and reflected wave will lead to a sharp increase in the temperature at the wall of blade. When the detonation wave propagates, the oscillation amplitudes of pressure and temperature at the turbine inlet are 70% and 75% respectively, and the detonation oblique shock will change the flow trajectory of the air flow, resulting in the flow direction deviating from the incident angle. Then the comparison between detonation and deflagration shows that the total pressure of detonation is higher and will have greater work potential. The torque generated by the blades under detonation has the characteristics of high-frequency oscillation, which may be detrimental to the operation of the engine.  相似文献   

3.
    
The present study deals with the implication of the novel diamond-shaped dual strut with a backward-facing step on the combustion characteristics of a cavity-based scramjet combustor. The dual strut with diamond shape is considered for the investigation since it triggers the flow separation leading to the disturbances in the flow especially at the top and bottom wall thus serving the flame holding purpose. Firstly, the combustion characteristics of a combustor with a single strut are compared and evaluated with a dual strut based combustor to portray the effect of a dual strut. A separate study is carried out to investigate the influence of spacing in a dual strut on the performance of the scramjet combustor. Our study reveals that the dual strut with a cavity greatly affects the formation of vortices, separation region, and recirculation region which is evident from an increase in the mixing and combustion efficiency. It can be observed that the formation of vorticity and the recirculation region is found to be larger due to the strong and multiple reflections of a shock in the case of the diamond-shaped dual strut with a backward-facing step injection as compared to the single diamond-shaped strut. Further, it is observed that the spacing(D) in the dual strut also affects the mixing and combustion performance. It is found that the value of mixing and combustion efficiency decreases with an increase in spacing independent of Mach number due to the presence of larger separation regions. It can also be observed that the length of the recirculation region occupies entire the cavity making flame stable when the spacing is the least. This is desirable as far as engine performance is concerned.  相似文献   

4.
    
It is vital to analyze the flame characteristics and identify the flame states efficiently in scramjet. Flame combustion and oscillation behaviors in a hydrogen-fueled cavity-stabilized scramjet combustor have been investigated in this study. A 500 Hz high-speed PLIF (planar laser-induced fluorescence) technique with a 20-cm-wide view field is introduced to characterize the combustion flow. The spatial distribution of the flame structure under different fuel injection conditions is studied. The results indicate that the position of the flame peak shifted downstream of the cavity when increasing the injection pressure to a high level. The dynamic characteristics of flames under different flow conditions are analyzed, and the correlation between flame features and hydrogen injection conditions is obtained. These flame features include the vertical range, the flow direction position of the peak flame, the flow direction position of the centroid, the vertical position of the centroid, the flame area, and the flame circumference. For the present cases, the flame of 4.0 Mpa is more unstable than that of 1.5 Mpa under any flow conditions. Moreover, an experiment based on feature extraction results shows that the KNN (K-nearest neighbor) classifier could achieve high accuracy for flame state recognition in this scramjet combustor.  相似文献   

5.
    
This study aims to understand the flow performance of a dual wall-mounted cavities in a strut-injector mounted scramjet combustor for steady-state and transient reacting conditions. Conventionally, two-dimensional Reynolds Averaged Navier-Stokes approach is adopted to compute the steady flow, whereas the current research employs Delayed Detached Eddy Simulation for predicting the unsteady flow characteristics as well. The calculated flow patterns, density, pressure, and temperature fields of dual cavities are compared with shadowgraph and wall pressure measurements from DLR experiments. The dual cavities position substantiates to explore the interplay between wave propagation and shear layer mixing characteristics. Employing a dual cavities arrangement accelerates toward the complete combustion relative to the baseline model. The combustion zone widens in the lateral direction as the dual cavities shift the shock train downstream of the strut injector owing to intense shock shear layer interactions. These cavities' existence significantly modifies the dominating frequencies and affects the strength of the diverging section's coherent flow structures.  相似文献   

6.
    
The shorter residence period of supersonic air in a scramjet combustor makes mixing and combustion challenging. Mixing augmentation occurs at the fuel-supersonic air interface. Multiple interactions between shock waves and the shear layer may significantly affect this inter surface. In this research, an attempt has been made to analyze how multiple oblique shock waves interact with the shear layer. The primary splitter plate combustor bottom wall is modified with a wavy-wall surface to ensure the development of multiple oblique shock waves. The internal flow field with and without a wavy wall surface has been analyzed by solving the two-dimensional Reynolds averaged Navier-Stokes equations and SST k-ω turbulence model. The reaction between ethylene fuel and the air is modeled with a global one-step reaction mechanism with finite rate eddy dissipation turbulence chemistry interaction. The flow disturbances with the wavy-wall surface have been evaluated by analyzing the numerical results like the flow structure, pressure, velocity, reaction rate, vortices, turbulence intensity, and interactions among shock wave, shear mixing, and boundary layers. The oblique shock waves induced from the wavy-wall surface significantly impact the mixing of fuel and air and successful reaction mechanism from the visualization of flow structure and concern results.  相似文献   

7.
    
In this research paper, passive method has been considered to improve the mixing and combustion efficiency of scramjet combustor. Modified and innovative strut injector designs have been developed from the reference of DLR scramjet. Strut is the mechanical component which is placed in the flow stream of supersonic airflow and used to inject the fuel. The newly introduced strut injector models are named as rocket and double arrow shape strut injectors. Numerical analysis of computational domains with innovative strut injectors has been carried out by considering the ANSYS – FLUENT 15.0, which is a numerical simulation tool. Shear stress transport model (SST k−ω model) has been considered for turbulence modeling under high speed flows. From the numerical results, it is observed that the compressed air entered into the combustion chamber is at higher pressure than the basic DLR scramjet model and it reduces the ignition delay. It is also found that both the rocket and double arrow strut models increases the boundary layer separation and vortex formation and therefore it enhances the better mixing of fuel and air and finally it improves the combustion efficiency.  相似文献   

8.
Numerical study on supersonic combustion with cavity-based fuel injection   总被引：1，自引：0，他引：1  
The present study describes the numerical investigations concerning the combustion enhancement when a cavity is used for the hydrogen fuel injection through a transverse slot nozzle into a supersonic hot air stream. The cavity is of interest because recirculation flow in cavity would provide a stable flame holding while enhancing the rate of mixing or combustion. Several inclined cavities with various aft wall angle, offset ratio and length are evaluated for reactive flow characteristics. The cavity effect is discussed from a viewpoint of total pressure loss and combustion efficiency. The combustor with cavity is found to enhance mixing and combustion while increasing the pressure loss, compared with the case without cavity. But it is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss.  相似文献   

9.
Plasma assisted cavity flame ignition in supersonic flows   总被引：5，自引：0，他引：5  
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10.
When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. The pulse jet transits to spherical shock wave with the increase in the strength of shock wave. The strength is dependent on the Mach number of shock wave, which attenuates by propagation distance from the open end. In this study, the mechanism of generating the unsteady pulse jet, the characteristics of the pressure distribution in the flow field and the emission of shock wave from straight circular tube which has the infinite flange at open end are analyzed numerically by the TVD method. Strength of spherical shock wave, relation of shock wave Mach number, distance decay of spherical shock wave and directional characteristics are clarified.  相似文献   

11.
In this paper, the initiation characteristics of the oblique detonation flow field induced by single- and double-wedge surfaces of finite length in a confined space are investigated. Numerical simulations with a detailed H2/air reaction and theoretical shock polar analyses are combined to study the influence mechanism of a complex wave system structure on the characteristics of the oblique detonation. The effects of expansion waves on the oblique detonation waves (ODWs) and their flow field characteristics for different equivalent ratios and geometric sizes are analyzed in single-wedge and double-wedge structures with the same inflow parameters. The results show that the length of the induced ODW is shorter in the double-wedge structure than in the single-wedge structure. For the single-wedge structure, the strength of the expansion wave increases, the wall temperature drops, and the characteristic length of the induction zone decreases with increasing deflection angle of the second wedge. If the strength of the expansion wave is sufficiently large, the ODW is initiated. For the double-wedge structure, the ODWs interact and form a complex wave system structure, consisting of a Mach stem, two reflected detonation waves and slip lines. The length and the temperature before and after the Mach stem decrease with an increase in the strength of the expansion waves. The effects of the expansion waves on the flow field of the ODW are relatively small at a large equivalent ratio and significantly larger at a small equivalent ratio.  相似文献   

12.
The mixing concept of fuel and air is the burning issue for hypersonic vehicles (scramjet) due to the less resident time of supersonic air in the combustion chamber. So far, significant research has been done for mixing enhancement and introduced different technologies; still, there is a lack of research for mixing improvement. Shock wave and shear mixing layer are the main parameters for investigating mixing criteria at supersonic speed. In this research, an innovative fuel injection strut has been designed to develop mixing enhancement by elevating multiple interactions between the shock wave and shear mixing layer. This new strut has been designed with the reference of the DLR scramjet combustor. From the reference of a wedge-shaped strut, a revolved (wedge shape – circular 3D) wedge strut has been modeled with the same fuel injection base points. This new strut's performance has been analyzed for mixing enhancement by visualizing the development of shock wave, shear-mixing layer, and their interactions. Three-dimensional numerical analysis has been carried out by solving the Reynolds-Averaged and Navier-Stokes (RANS) equations. A comparison of results has been made for the basic wedge and new strut and identified the increase in multiple interactions of the shock wave and shear layer, which leads to an increase in mixing enhancement. For the new strut, complete mixing has been achieved within a distance of 0.180 m with an average increase in mixing efficiency of 9% and increased pressure losses of 12%.  相似文献   

13.
In this paper,some preliminary calculations and the experiments were performed to figure out the flow field,inwhich some rods were normally inserted into the main flow surrounded by a porous cavity.As a result,it is foundthat the starting shock wave severely interacts with the rods,the bow shock wave,its reflections,and the porouswall,which are numerically well predicted at some conditions.Moreover,inserting the rods makes the pressureon the upper wall in the porous region increase when the main flow in the porous region is completely supersonic.The calculations also suggest that three rods cause the widest suction area.  相似文献   

14.
    
The objective of this study is to apply the finite difference method (FDM) scheme to generate profiles of velocity, vorticity, pressure, temperature, and density of the flow field inside the chamber of a rotating detonation engine. In addition, this study discusses the Kuo's algorithm used in the computation of Chapman-Jouguet (CJ) variables. A new computational algorithm is introduced to compute the CJ variables, the shock, and the post-shock conditions. Five different fuels are tested, H2–O2, H2-air, CH4-air, C2H6-air, and C2H2-air. The results show good performance for the FDM scheme, and the new algorithm is adopted in this study to perform all CJ calculations. The new algorithm's results are compared with the experimental data available for the tested fuels and show close results. Another important result is that the highest vorticity forms along the slip line of the combustion chamber, then it gradually shrinks along the path of the slip line.  相似文献   

15.
ＵｎｓｔｅａｄｉｎｅｓｓｏｆＳｈｏｃｋＷａｖｅ／ＢｏｕｎｄａｒｙＬａｙｅｒＩｎｔｅｒａｃｔｉｏｎｉｎＳｕｐｅｒｓｏｎｉｃＣａｓｃａｄｅＵｎｓｔｅａｄｉｎｅｓｓｏｆＳｈｏｃｋＷａｖｅ／ＢｏｕｎｄａｒｙＬａｙｅｒＩｎｔｅｒａｃｔｉｏｎｉｎＳｕｐｅｒｓｏｎ...  相似文献   

16.
The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand the detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee's total variation diminishing (TVD) scheme is used to solve the unsteady two-dimensional compressible Euler equations. The Mach number Ms of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two-parallel tube  相似文献   

17.
In this paper, a thermal wave in the bath of superfluid helium II is measured by a new type of superconductor temperature sensor under different heat fluxes and bath temperatures, and at the same time, a thermal shock wave is also studied experimentally and theoretically. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 419–425, 2001  相似文献   

18.
INTRODUCTIONUnsteadycompressiblegasflowthroughaductisoftenencoullteredinmanyengineeringapplicationsandhasbeeninvestigatedbymanyresearchers.Whenapressurewavegeneratedinsideaductisdischargedfromanopenendoftheduct.animpulsivewave,whichcanbefrequentlycha...  相似文献   

19.
Introduction The elbow is one of the important elements used in pipe lines, and it is very important to clarify the propagating phenomena of shock waves through the elbow for engineering applications. Although some investigations of the propagating shock in the single and double elbows have been carried out[1?The working gas is air. The numbers of the grid in the computational domain are 251·(a) Type 4-1 (b) Type 4-2 Fig.3 Pressure distributions on each wall the merging with the 2nd shock…  相似文献   

20.
    
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.  相似文献   

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