Skin Friction Measurements for Recirculating Normal Shock/Boundary-Layer Interaction Control

Abstract

Skin-friction measurements for a normal-shock/boundary-layer interaction with several recirculating flow control methods have been conducted in a planar Mach 1.4 wind tunnel. The skin friction has been measured along the spanwise centerline and downstream of the interaction using the laser interferometry skin-friction (LISF) technique, which optically detects the rate of thinning of an oil film applied to the test surface. Velocity profiles measured by laser Doppler velocimetry at the same locations as the LISF measurements in the interaction were also used to evaluate the skin friction. Comparison of the two measurement techniques for skin friction is found to show reasonable agreement. Various configurations of the mesoflap arrays of different shapes and thicknesses were examined, and the results were compared to cases of both a solid wall with no control mechanisms and conventional recirculating passive flow control with a porous plate. Of the various mesoflap arrays tested, one mesoflap array provided higher skin friction downstream of the interaction, and as such tends to have better recovery from flow separation. However, all values of skin friction for the mesoflap arrays and the porous plate were found to be lower than for the solid-wall reference case. As such, the flow downstream of these control systems can be more susceptible to separation for this particular condition, although the control systems may reduce viscous drag in external flows.