The receptivity problem for O(1) wavelength Görtler vortices

In this paper we make an investigation of the receptivity of boundary layer flows to Görtler vortex modes. A study by Denier et al. (1991) of the generation of vortices by wall roughness elements concluded that such elements are extremely poor as mechanisms to stimulate short wavelength modes. That work also examined the equivalent problem pertaining to O(1) wavelength modes but that analysis was flawed. We re-examine this problem here and demonstrate how the form of the wall roughness is crucial in determining the vortex stability characteristics downstream of the roughness. In particular we investigate the cases of both isolated and distributed forcing functions and show that in general a distributed function is much more important in generating vortices than are either isolated roughness or free-stream disturbances.