Swept-wing boundary-layer receptivity to free-stream vortical disturbances

Abstract

Abstract Content of image described in text. Direct numerical simulations are performed to investigate the receptivity of a swept-wing boundary layer to unsteady free-stream vortical disturbances in the nose region of the airfoil. An infinite wing with a sweep angle of 35 Superscript ring ∘ $^\circ$ and at free-stream Mach number of 0.65 has been employed, and single Fourier modes of vortical disturbances are introduced far upstream. It is shown that leading-edge-parallel vortical two-dimensional waves are most receptive, but the induced travelling crossflow modes are typically too small in amplitude to directly trigger transition. The interaction with roughness elements, however, enhances the amplitudes substantially for one type of free-stream disturbances, and travelling-wave dominated transition occurs. The investigation may help in understanding the problem of unreliable transition control by the upstream-flow-deformation or distributed-roughness-element technique in flight, where at the same time a proper working is typically reported in wind-tunnel experiments.