Boundary layer receptivity to free-stream turbulence and surface roughness over a swept flat plate

Abstract

An experimental study of the receptivity of disturbances and their subsequent development into a three-dimensional boundary layer has been carried out. The three-dimensional boundary layer was set up using a flat plate with a swept leading edge and a pressure gradient using a displacement body at the ceiling of the test section. Low level free-stream turbulence was generated with five different screens and was shown to generate traveling crossflow modes for all but the lowest turbulence level, i.e., for Tu>0.2%, where instead a stationary crossflow disturbance dominated. Stationary crossflow disturbances were triggered by small cylindrical roughness elements arranged in an array. For high enough roughness Reynolds number (Rek) stationary disturbances growing exponentially were seen and their amplitude seems to scale with Rek2.3.