DISTRIBUTED EXCITATION OF TOLLMIEN-SCHLICHTING WAVES BY VORTICAL FREE-STREAM DISTURBANCES

Nonlocalized receptivity to vortical free-stream disturbances is analy zed for a Blasius boundary layer over a wavy surface. Vortical disturb ances are rescaled through an interaction with steady disturbances gen erated by the surface waviness. The rescaled disturbances provide a di stributed energy transfer to the natural eigenmodes when conditions ar e close to resonance; this occurs in the neighborhood of the lower bra nch of neutral stability. Downstream of the energy transfer, the trave ling wave solution is dominated by the natural eigenmode. Forcing from the vortical disturbances is concentrated in the outer region of the boundary layer. This leads to a relatively weak receptivity as compare d to the acoustic problem. Total receptivity amplitudes are approximat ely ten times larger than for localized vortical receptivity, but appr oximately fifty times smaller than for nonlocalized acoustic receptivi ty.