Receptivity of a boundary-layer flow to a three-dimensional hump at finite Reynolds numbers

The receptivity of boundary-layer flow to a three-dimensional hump (an array of humps) at a finite Reynolds number is solved with the help of an expansion of the linearized solution of Navier-Stokes equations into the biorthogonal eigenfunction system. There are two counterrotating vortices behind the roughness element that bring the high-speed fluid down into the wake region. Depending on the geometry, two relatively high-speed streaks could be observed in the wake downstream from the hump. The results for the flow-field structure are in qualitative agreement with available computational data. The quantitative discrepancy is attributed to the nonlinear character of the receptivity mechanism at the parameters considered in the computational studies.