LEADING-EDGE RECEPTIVITY IN 3-DIMENSIONAL CLASSICAL BOUNDARY-LAYERS

Theory and computations are presented for the receptivity of a three-d imensional boundary-layer flow on a flat surface to a large-scale low- frequency periodic external forcing. The basic-state boundary layer an d the disturbances are governed by the classical (non-interactive) Pra ndtl equations with a prescribed pressure gradient. The disturbance so urces in the case of (i) injection/suction through the wall or (ii) fr ee-stream oscillations interacting with irregularities in the wall geo metry are assumed to be concentrated close to a sharp leading edge whe re the main boundary layer is approximated by a similarity solution of Loos (1955). It is shown that time- and spanwise-periodic perturbatio ns introduced by (i) or (ii) develop downstream as a spatially growing instability wave of the type examined in Timoshin (1995), modified ho wever by the effects of the flow nonparallelism. An algebraic form of instability in the boundary layer on a rounded leading edge is also di scussed.