Numerical study of boundary-layer receptivity on a swept wing

Authors: Tempelmann, D., Schrader, L.-U., Hanifi, A., Brandt, L.B., Henningson, D.S.H.
Document Type: Conference
Pubstate: Published
Journal: AIAA Paper
Volume: 2011-3294  
Year: 2011


Direct numerical simulations (DNS) of the flow over a wing with 45 degrees sweep and -4 degrees angle-of-attack are presented. This flow configuration was investigated in a series of wind-tunnel experiments at the Arizona State University (ASU). Here, we examine the boundary-layer receptivity to surface roughness and to single vortical free-stream modes. The roughness is modeled by a shallow circular disk and is identical with one single element of the spanwise roughness array considered in the ASU experiments. The boundary layer develops a steady crossflow mode downstream of the roughness. The spatial evolution of the modal amplitude obtained by the DNS is in excellent agreement with a solution to the nonlinear parabolized stability equations (NPSE) while being lower than that measured in the experiments. The reasons for this discrepancy are yet to be determined. Possible explanations are the presence of traveling crossflow waves due to background free-stream turbulence in the experiments or the slight difference between the numerical and experimental pressure gradients at the roughness site. Stationary crossflow vortices can also be triggered by zero-frequency free-stream vortical modes. We consider two types of mode, carrying streamwise and vertical vorticity. Both modes give rise to nonmodal disturbances near the leading edge, which soon evolve into a steady crossflow mode. The boundary layer is found to be somewhat more receptive to the streamwise-vorticity mode than to the chordwise vorticity.