Wall pressure fluctuations in supersonic boundary layers over compression ramps with different turning angles

Abstract

In the present study, we investigate the influences of shock intensity on wall pressure fluctuations by performing direct numerical simulations of the supersonic turbulence boundary layers over compression ramps with different turning angles. We found that as the turning angle increases, the low-frequency motions of the separation shock are enhanced, accompanied by the enlarged energetic pressure structures with the lower convection velocities. By inspecting wavenumber-frequency spectra under the assumption of streamwise homogeneity, we further identified two energetic modes convected at different velocities. The one with the lower convection velocity, namely the `slow mode', inherited from the upstream pressure fluctuations of the turbulent boundary layer, is decelerated when passing through the oblique shock, during which the `rapid mode' with pressure fluctuations convected at higher speeds are generated. The increasing turning angle decelerates the slow mode and intensifies the fast mode. The reconstruction of the flow field suggests that the rapid mode is associated with the shear layer generated adjacent to the interaction zone while the slow mode with the G{\"o}rtler vortices on the ramp.