Receptivity Investigations

Abstract

For the most part, our investigations have been experimental. They have involved the use of a low-noise, low-turbulence, subsonic wind tunnel with a test cross-section 15” by 15”. Laminar boundary layers are grown on a polished aluminum flat plate with internal damping. The plates are all 1/2” thick and are fitted with a 6:1 semi-elliptical leading edge. The first experiments, reported by Shapiro [1977], involved excitation by a nearly plain, pure tone, acoustic wave travelling downstream over the test plate. A now classic standing wave pattern was found in the boundary layer (Figures 1 and 2). The wavelength of the standing wave was that of a Tollmien–Schlichting (T-S) wave at the frequency of the acoustic wave.