Vorticity production at the edge of a slit by sound waves in the presence of a low-Mach-number bias flow

Vorticity production by low-frequency sound waves impinging on a screen perforated with a slit is studied in the presence of a steady low-Mach-number mean flow through it. A Kutta condition is invoked at the rim of the slit to determine the strength of the shed vortex sheets. It is found that, unlike the case of a circular aperture, the strength depends not only on the Strouhal number but also on the Mach number. An attempt is made to apply the results to the problem of transmission of sound waves through a uniformly perforated screen.