SPATIAL EVOLUTION OF CONTINUOUS-MODE PACKETS LOCALLY FORCED IN A BOUNDARY-LAYER FLOW

The excitation of two-dimensional continuous spectrum waves by the loc al harmonic force in a boundary-layer flow is considered. Analysis is performed within linearized Navier-Stokes equations for an incompressi ble parallel flow. An expression for the field of hydrodynamic disturb ances outside the forcing region is obtained by employing the method o f normal waves and the Briggs criterion which determines the direction of the wave spreading. The spatial structure of the continuous spectr um disturbances excited by a point force which models the effect of a small vibrating ribbon is determined. It is shown that a convective wa ve appears in the boundary layer at a considerable distance from the s ource.