Rayleigh Lecture 2007: Flow-surface interaction noise

A review is given of the theory of vortex sound with emphasis on sound production by vortex–surface interactions involving rigid and deformable, compact and noncompact moving bodies. The analysis is facilitated by use of the ‘compact’ approximation to the acoustic Greenʹs function in cases where the solid surface is either acoustically compact or, for noncompact bodies, where the surface supports locally compact regions of ‘noisy’ flow identified by the presence of singularities in the ‘Kirchhoff vector’ of Greenʹs function. The noncompact problem of the compression wave generated by a high-speed train entering a tunnel is discussed as an example of how accurate predictions of sound generation by identified distributions of vorticity can frequently be made by analytical means when the more conventional numerical approach becomes intractable.