The analysis of the influence of viscosity on diffraction of aircraft noise by edges is exemplified by the mathematical problem of diffraction of an acoustic plane wave by a thin rigid screen. The linearized equations of compressible fluid mechanics with viscosity included are considered with the overall disturbance field regarded as a sum of acoustic and vorticity fields. Each such field, for disturbances of fixed frequency, is governed by a separate Helmholtz equation, but they are coupled by the no-slip and nonpenetrability conditions at the screen’s surface. With viscosity taken into account, the perturbation-induced fluid velocity near the edge is not infinite, but is nevertheless very large when the viscosity is small, even though the velocity vanishes identically at the surface.

This content is only available via PDF.
You do not currently have access to this content.