Generation of Supersonic-Flow Disturbances by Two-Dimensional Roughness in a Turbulent Boundary Layer

Supersonic-flow disturbances generated by two-dimensional roughness on the wall of a wind-tunnel test section are simulated. The case of a small roughness height compared to the thickness of the turbulent boundary layer on the wall is considered. The studies involve numerical simulations taking into account the turbulent boundary layer on the wall and experiments using a hot-wire anemometer. The effect of the height and width of the two-dimensional roughness and the flow Mach number on supersonic-flow disturbances are studied. It is established that the presence of the two-dimensional roughness causes a stationary free-stream disturbance in the form of an N-wave and the occurrence of a region with increased nonstationary pulsations over a wide spectrum. Increasing the height of the two-dimensional roughness is shown to increase the amplitude and spatial scale of the disturbance generated in the flow. For a small roughness width, the free-stream disturbance takes the shape of an N-wave; as the width increases, the disturbance amplitude remains unchanged and the N-wave splits into two shocks. The spatial scales of the mean-flow disturbance are compared for a fixed roughness geometry and Mach numbers of 2 and 2.5.