| Ramjet wih embedded rocket,as one of the power plant schemes which can effectively meet the requirements of high altitude penetration and mobile interception of high-speed aircraft,has a good development prospect.The subsonic-supersonic flow mixing in the combustion chamber has an important influence on the performance of the engine,and is also a very important basic research topic in the field of fluid dynamics.In this paper,an experimental system for the investigation of subsonic and hypersonic mixed flow of rocket gas and subsonic ramjet air in the combustion chamber of an embedded rocket ramjet is studied.The flow aerodynamic parameters and the flow field are studied by using ice crystal tracing plane laser scattering(IC-PLS),schlieren technique,temperature measurement technique and large eddy simulation(LES)The influence of geometric parameters and thermal conditions on the development characteristics of subsonic-supersonic shear layer is obtained.The flow field structure of subsonic-supersonic shear layer and the influence law of different parameters on the development of shear layer are obtained.The hybrid enhancement characteristics of lobes are proposed and verified,which provides theoretical basis for efficient combustion organization and optimization design of embedded rocket ramjet.The main contents and conclusions of this paper are as follows(1)Based on IC-PLS technology,the influence of pressure matching on the development characteristics of subsonic-supersonic shear layer is studied.It is found that the pressure mismatch of subsonic-supersonic shear layer is not conducive to the growth of shear layer.The calculation formula of dimensionless shear layer thickness growth rate considering pressure mismatch is established.It is considered that the inhibition effect of pressure mismatch on the development of shear layer mainly depends on the change of actual convective Mach number and the compression effect caused by the pressure difference.(2)Schlieren technique and large eddy simulation(LES)are used to study the effect of confined scale on the flow field structure and development characteristics of subsonic-supersonic shear layer.The results show that the limited scale has a critical effect.When the confined scale is larger than the critical value,the confined space has little effect on the development of the shear layer;when the confined scale is less than the critical value,the development of the shear layer will be limited by the wall The growth rate of shear layer thickness decreases with the decrease of limited scale.The critical value of dimensionless restricted scale is 5.6 when the dimensionless length is25.(3)The results show that when the exit height of supersonic flow is small,the initial development of shear layer will be disturbed,and the initial thickness of shear layer will increase faster;however,the interaction between the upper and lower shear layers in the downstream will restrict its development;on the whole,the growth rate of shear layer thickness will be affected by the central flow The limitation of scale.(4)Large eddy simulation(LES)and IC-PLS were used to study the influence of the thickness of the separator on the development and evolution of the subsonicsupersonic shear layer.It was found that with the increase of the thickness of the separator,strong disturbance occurred in the backflow region behind the steps of the baffle,which promoted the rapid instability and rolling up process of the transverse vortex in the shear layer,thus accelerating the roll up of the flow direction vortex and enhancing the mixing of the subsonic-supersonic flow.(5)The effect of wedge-induced shock wave on the development of shear layer in ultrasonic flow was studied by using ic-pls technology.The 3D fine flow field structure of interaction between wedge induced shock wave and subsonic-supersonic shear layer was obtained.The results show that wedge induced shock can promote the development of shear layer when the wedge angle is less than 10 ° and is not conducive to the development of shear layer when the wedge angle is greater than or equal to 10 ° If it is caused by the strong compression effect behind the shock wave,it is also found that the large-scale vortex can induce the shock wave to bend.(6)Based on the experimental system of hot subsonic-supersonic shear layer in confined space and large eddy simulation method,the influence of supersonic flow temperature on the growth characteristics of subsonic-supersonic shear layer is studied.The results show that the increase of supersonic flow temperature makes the compressibility of subsonic-supersonic shear layer increase and the initial thickness of shear layer decrease;meanwhile,the increase of temperature difference promotes the increase of temperature gradient,the acceleration of heat transfer and the increase of temperature shear layer In the downstream of the flow field,the combination of the upper and lower shear layers further accelerates the air mixing.(7)Based on the understanding of the development characteristics and influence law of subsonic-supersonic shear layer,two kinds of mixing structures,sinusoidal lobe and rectangular lobe,were designed,and the experimental research on mixing technology of subsonic-supersonic shear layer was carried out by using ic-pls technology.The results show that the sinusoidal lobe structure has better mixing effect than the rectangular lobe structure;the wavelength of the sinusoidal lobe structure has a great influence on the mixing effect,and the mixing effect is very strong when the wavelength is big,but it will bring negative impact if the wavelength is little.Under the condition of this paper,when the ratio of the lobe wavelength to the flow length is greater than or equal to 1,the lobe structure can have a strong mixing effect. |
