Experimental investigation of asymmetric streamwise vortices in a turbulent boundary layer

摘要

The induced flow-field behind passive vane type vortex generators subject to controlled inflow asymmetry (or skewed inflow) is investigated in this paper. The vortex generators are scaled on the order of approximately a quarter of the boundary layer height at the location of the VGs and are mounted on a flat plate inside a turbulent boundary layer wind tunnel. Stereoscopic-Particle Image Velocimetry is used to measure the flow field aft of the VG array. Evolution of salient vortex properties is presented and sensitivity to the skew angle is demonstrated. The integral boundary layer properties are additionally analysed. More pronounced local effects are seen with increasing yaw angle due to the increasingly asymmetric vortices. The effect on spanwise averaged shape factor is similar to the axial flow case, in this specific case with a zero-pressure gradient turbulent boundary layer. However, it appears that increasing skew delays the process of streamwise-momentum en-trainment, causing a slower overall development of the shape factor, compared to the axial flow case. This may have important implications for flow control on airfoils experiencing strong pressure gradients.