Acoustics of an Irrotationally Moving Perfect Gas

The propagation and radiation of sound in a stationary flow of a perfect gas is formulated as initial-boundary value problem of a hyperbolic differential equation with space dependent coefficients. This equation and a corresponding equation for sinusoidal vibrations of the source, together with a proper radiation condition, are the basis for the generalization of most fundamental theorems of conventional acoustics as, theorem of reciprocity, Helmholtz formula, energy balance, etc. The sound fields of specific sources and estimates of the influence of small regions of rotational flow (boundary layer) are discussed.