Study On Aerodynamic Characteristics Of A Scramjet Nozzle

Scramjet has the advantages of simple structure,high thrust to weight ratio and wide application prospect.But the flow field structure is very complex,so it is important to study the three-dimensional flow field structure of scramjet.In this paper,SST K-ω and LES are used to simulate the steady and unsteady flow field of three-dimensional scramjet nozzle.After the grid independence is verified,the dimensionless pressure value of the nozzle wall centerline and shigeya are calculated The accuracy and reliability of the experimental results are demonstrated by comparing the experimental results of Shigeya.W and others,and the necessity of three-dimensional grid computing is demonstrated by comparing with the calculation results of two-dimensional grid.Based on the analysis of the density,Mach number contour and vorticity distribution of different sections in the steady results,the structures of the expansion wave,shock wave and shear layer in the three-dimensional flow field are determined,and the formation reason and structure distribution of the streamwise vortices in the steady state are determined by the velocity vector diagram.Based on the unsteady velocity vector diagram of different cross sections,the variation law of the vortices at different positions in the flow field with time and the location of oscillation in the flow field are determined.Finally,the Fourier mode decomposition technique is used to analyze the velocity field of the streamwise vortices in the flow field,and the amplitude frequency curves on different sections are obtained.According to the time-domain evolution results,it is found that the oscillation region in the external nozzle flow field is mainly in the flow field near both sides of the upper wall boundary layer,while the wake flow field is The middle oscillation is concentrated at the streamwise vortex in the center of the flow field,and mainly shows the velocity oscillation,the flow field at other locations has oscillation phenomenon,the amplitude is not large,which is not the main oscillation form under this mode.