On local boundary-layer receptivity to vortical disturbances in the free stream (Q2774092)

The author presents a second-order asymptotic theory based on the triple-deck formulation. The asymptotic approach allows to treat vortical perturbations with a fairly general vertical distribution, and confirms \textit{A.J. Dietz's} conclusion [J. Fluid Mech. 378, 291-317 (1999)] that for the convecting periodic wake in his experiments, the receptivity is independent of its vertical structure and can be fully characterized by its slip velocity at the edge of the boundary layer. As in the case of distributed vortical receptivity, dominant interactions that generate Tollmien-Schlichting waves take place in the upper deck as well as in the so-called edge layer centred at the outer reach of the boundary layer. The author derives a superposition formula in the case of multiple roughness elements. A comprehensive comparison is made with Dietz's experimental data, and an excellent quantitative agreement has been found for the first time, thereby resolving some uncertainties about this receptivity mechanism.