An Experimental Investigation of Passive Shock/Boundary Layer Interaction Control on an Airfoil: Unsteady Measurements

Summary

During an experiment at high subsonic speeds on a two-dimensional airfoil with a passive system for the control of shock waves, unsteady pressure measurements were performed via a porous skin and an underneath 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.