The Scattering of Sound by a Vortex Sheet

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Abstract
The effect of the radiation from an acoustic point source on the vortex sheet separating two fluids in relative motion is investigated. A supersonic speed of flow is allowed for and sources which are either harmonically varying or pulsed in time are included. It is discovered that waves due to Helmholtz instability are always present and dominate other disturbances whatever the Mach number M. This contrasts strongly with excitation by a line source where instability disappears when M > 2□2. There is a bow wave moving ahead of other disturbances and, if M > 2, a second bow wave appears, behind the first bow wave but in front of other waves. If M > 2, there is a neutral stability wave which is singular at its front. In addition, if M > 2□2, further waves are generated which display the same kind of singularity.

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