Experimental investigations of the boundary layer receptivity, on the sharp leading edge of a flat plate, to acoustic waves induced by two-dimensional and threedimensional perturbers, have been performed for a free-stream Mach number M ∞ = 5.92. The fields of controlled free-stream disturbances were studied. It was shown that two-dimensional and three-dimensional perturbers radiate acoustic waves and that these perturbers present a set of harmonic motionless sources and moving sources with constant amplitude. The disturbances excited in the boundary layer were measured. It was found that acoustic waves impinging on the leading edge generate Tollmien-Schlichting waves in the boundary layer. The receptivity coefficients were obtained for several radiation conditions and intensities. It was shown that there is a dependence of receptivity coefficients on the wave inclination angles.

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The objective of this review is to provide a critical evaluation of linear stability theory for wall-bounded shear flows, with an emphasis on results, not techniques. The results deal with applications to different flowfields related to aircraft systems. Because the flight condition is usually a low-disturbance environment, stability plays an important role in the transition process. Linear stability theory is not a new topic, so emphasis is placed on the most recent accomplishments.