The laminar boundary layer instability excitation of an acoustic resonance

✍ Scribed by F.S. Archibald

• Publisher: Elsevier Science
• Year: 1975
• Tongue: English
• Weight: 935 KB
• Volume: 38
• Category: Article
• ISSN: 0022-460X
• DOI: 10.1016/s0022-460x(75)80054-x

✦ Synopsis

Tollmien-Schlichting waves on a 10C4 airfoil spanning the working section of a low speed wind tunnel have been discovered as the source of excitation of the Parker fl-mode resonance. The feedback loop of the self-excited resonance is completed by acoustic coupling to the origin of the instability at the critical Reynolds number and occurs within the inner region of this laminar boundary layer instability. The coupling frequency range and amplification rate are predictable from instability theory. In the self-exciting system the sound enables the boundary layer to remain attached and laminar to the trailing edge which is far past the mid-chord separation point calculated by using Thwaites' method. In this case the unsteady Kutta condition does not hold to the order of the instability pressure fluctuations in the boundary layer.