L.M. Campos

It is shown that significant attention of sound can occur in a boundary layer, when a critical level exists (§1); the critical level is the point where vanishes the Ooppler shifted frequency, calculated from wave frequency and horizontal wavenumber parallel to the wall (§2), and its existence and location depends on the shear velocity profile (§3). The critical level acts as an acoustic "valve" (§4), amplifying waves propagating in one direction, and attenuating in the other. We solve exactly the acoustic wave equation in an exponential shear flow and show (§5) that there are solutions propagating or evanescent in the free stream. These solution are extended to the whole flow region up to wall, accross the critical level, which is a singularity of the wave equation (§6). The waveforms, amplitudes and phases of the acoustic pressure are plotted versus distance from the wall for a variety (§7) of combinations of frequencies, wavenumbers and free stream mach number, from subsonic to supersonic.

DGLR/AIAA 14th Aeroacoustics Conference, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 8 Seiten

DGLR-Bericht, 1992, 1992-03, DGLR/AIAA 14th Aeroacoustics Conference - Proceedings; S.342-349; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1992