A well posed acoustic analogy based on a moving acoustic medium

Abstract

For flows of a lossless gas, the stagnation enthalpy obeys a linear convected wave equation with coefficients which depend on the flow variables. This equation is self-adjoint and one has a reciprocity relation between source and observer. It fulfills for subsonic flow a quadratic conservation equation implying stability. It is taken as basis for an acoustic analogy and is applied to the sound generation by the collision of a convected vortex and a rigid cylinder.