An Experimental Investigation of Passive Shock/Boundary - Layer Interaction Control on an Aerofoil: Unsteady Pressures.

Abstract

During an experiment at high subsonic speeds on a two-dimensional aerofoil with a passive system for the control of shock waves, unsteady pressure measurements were performed via a porous skin and an undersurface cavity. Passive control caused by the pressure gradient across the shock wave induces a secondary flow through the surface and underlying cavity. This secondary flow causes an injection into the upstream boundary layer and a suction from the boundary layer upstream of the shock. With this, the main shock wave is weakened. The stationary measurement does not show reduced drag as expected but an increased overall drag instead. The unsteady pressures show an increase in the higher frequency fluctuations downstream of the shock, indicating a thickening of the boundary layer which is the reason for the increase in the viscous drag. This report was prepared as the final technical report of the DLR Institute of Aeroelasticity's contribution to the EU Euroshock programme.