Detailed directivity measurements of aerodynamic sound sources

The sound radiated by a vibrating surface can be modelled using combinations of elementary sources but for aerodynamic noise sources it is less clear how to do so. It is proposed here that the arrangement and number of ideal sources required to represent aerodynamic sources may be revealed by their directivity pattern. Presented in this paper are some aerodynamic sound source directivity results obtained from a loudspeaker robot in the University of Salford's full anechoic chamber. This novel use of the apparatus produces plots of sound pressure amplitude on a spherical surface obtained by incrementally rotating the aerodynamic sound source with respect to a fixed microphone. Balloon plots of aerodynamically generated sound source directivity are presented and the representation of aerodynamic sound sources using elementary sources or multipoles is discussed.