Influence of boundary-layer state on development downstream of normal shock interactions

Abstract

Flat plate experiments investigating flow development downstream of normal shock wave–laminar boundary layer interactions are reported. Laminarity is desirable for low drag, but problems are expected at shock interactions due to separation, leading to un- steadiness and large boundary layer growth. A flat plate with elliptical leading edge profile is used to generate a laminar boundary layer, which encounters a Mach 1.2 normal shock at a Reynolds number of 1.6x10^6. Upstream of the interaction, the boundary layer is too thin for detailed measurement, but schlieren images are presented and laser Doppler ve- locimetry results reported downstream. For comparison, similar measurements are then made with trips located upstream. Far downstream, shape factor and skin friction are seen to be independent of incoming boundary layer state, contrary to expectations: although separation does occur in the laminar case, it is very thin and the anticipated impact on the boundary layer health is not seen. In fact, an equilibrium turbulent boundary layer is recovered far sooner downstream and is thinner than in the tripped cases, which exhibit attached turbulent interactions. In summary, normal shock wave–laminar boundary layer interactions did not exhibit the anticipated detrimental effects, and instead appear quite benign.