| The study of the boundary layer is a classical problem of fluid dynamics.And with the development of high-speed aircraft technology,the study of high-speed boundary layer flow is of great significance in scientific research and engineering application.The experimental model of expansion and compression combined corner is a geometry simplified from a part of the shape of high-speed aircraft.In supersonic flow,with the experiment of schlieren,particle image velocimetry,plane laser scattering technology,and high-frequency response pressure transducers,the high-speed boundary layer near the expansion corner and the shock wave boundary layer interactions near the expansion and compression combined corner are investigated.Through the study of the boundary layer near an expansion corner,it is found that within a certain range after the expansion position,the boundary layer develops in the direction of the incoming flow,the thickness of the boundary layer increases significantly,the flow turbulence decreases,the size of the flow structure increases,and the small-scale structure disappears inside the boundary layer near the wall.In the range far from the position of the expansion corner,the flow begins to develop in the direction of the wall,and the turbulence begins to return to the level of the incoming flow.Research on the boundary layer near the expansion and compression combined corner shows that with the influence of the expansion corner,the large-scale flow separation occurs in the process of shock wave boundary layer interactions near the compression ramp.And the size of the separation region increases obviously when large-scale or small-scale flow separation occurs.The pressure rise at the separation point decreases,and the range with the influence of interactions increases.When large-scale separation occurs,the characteristic low-frequency spectrum signal related to the unsteadiness of the shock wave boundary layer interaction is observed.But the fluctuation of velocity and wall pressure related to the unsteadiness of the shock wave boundary layer interaction is reduced significantly.Further investigation of the boundary layer near the compression ramp at different positions after the expansion corner shows different phenomena.When the expansion corner is closer to the compression corner,with the interactions of the expansion fans and the shock wave,large-scale flow separation occurs when the angle of the compression ramp is large.The size of the separation region is approximately equal to the size of the expansion section and the separation point is located behind the expansion corner.When the angle of the compression ramp is small,the flow direction size of the small-scale flow separation zone also increases.During the process of interactions,the pressure rise at the separation point is reduced,and the interaction influenced range is also reduced and located behind the position of expansion.When large-scale separation occurs,the unsteadiness of shock wave boundary layer interactions is significantly suppressed,the characteristic low-frequency spectrum signal of wall pressure fluctuations no longer appears.And the amount of velocity and wall pressure fluctuations within the range influenced by interactions is reduced more significantly. |
