ACOUSTICS IN MOVING MEDIA ACOUSTICS IN MOVING MEDIA

fillment of the requirements for the degree of Doctor of Philosophy. This thesis is concerned with two types of problems in-volving moving fluids and sound. The first problem is to determine the qualitative conditions necessary for instability due to infinitesimal acoustic disturbances. The particular technique used here is to as-sume that the disturbances are fixed in space while the fluid flows past them. This viewpoint is applied to the questions of turbulence onset and resonator excitation. The second problem is to examine some of the quantita-tive properties of an interface between two media in relative motion. In particular, the sound field due to a source near such an interface is calculated. It is shown that the sound field can be approximated in a closed form by a saddle point integration, and this will be a valid approximation for distances from the source which are large as com-pared to the wave length of the emitted sound. This situation is gen-eralized to the study of the characteristics of a channel formed by two parallel velocity discontinuity interfaces. Then, it is further generalized to include the possibility of a plate or membrane along the interface separating the two media in relative motion. The sta-bility of the interface is discussed as each of the various cases arises