Abstract
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.
