Roughness-induced receptivity to crossflow vortices on a swept wing

Abstract

The generation of stationary crossflow vortices on the 45 degree swept NLF (2)-0415 airfoil at the Arizona State University Unsteady Wind Tunnel (AIAA Paper No. 96-0184, 1996; Ph.D. thesis, Arizona State University, 1996) is analyzed using a finite Reynolds-number linear receptivity theory. The receptivity theory is based on the locally-parallel flow approximation and also neglects surface curvature. The vortices are excited by a spanwise periodic array of circular roughness elements located near the attachment line. The amplitudes of the crossflow vortices at the source location are computed and compared with the experimental results. In general, the agreement is remarkably good. This suggests that the combined effect of nonparallel flow and surface curvature on the receptivity is not significant for the range of conditions considered. The linear analysis captures the receptivity variations with Reynolds number, roughness geometry, and roughness location. When the roughness height is small, the initial amplitudes of the roughness-generated crossflow vortices are well predicted using the finite Reynolds-number receptivity theory. Nonlinear effects appeared to become significant only when the roughness height exceeds about 10% of the local boundary layer displacement thickness.