Aero-thermoacoustics (The Generation of Sound by Turbulence and by Heat Processes)

Abstract

An analysis of the general equations of motion of a viscous compressible fluid leads to the identification of three modes (vorticity, compression and entropy modes) of energy associated with the fluid. Interaction between these modes gives rise to acoustical phenomena, of which some are of great interest to the study of aircraft noises.The first part of this report deals with acoustical effects resulting from the interaction of a vorticity and a compression mode. It considers in detail the generation of sound from turbulence as encountered in a jet and in a boundary layer, and the scattering of sound from turbulence.In the remaining part the interaction of the entropy mode with the compression mode is discussed. Special emphasis has been placed on the study of heat-maintained vibrations as encountered in Rijke's phenomenon and in flame-driven oscillations.The article concludes with a speculative discussion of acoustical phenomena in which the couplings between the three modes are equally important.