National Aeronautics and

The propagation of acoustic waves originating from cylindrical and spherical pulses, in a non-uniform mean #ow, and in the presence of a re#ecting wall is investigated by Hardin and Pope approach using compact approximation of spatial derivatives. The 2-D and 3-D stagnation #ows and a #ow around a cylinder are taken as prototypes of real world #ows with strong gradients of mean pressure and velocity. The intensity and directivity of acoustic wave patterns appear to be quite di#erent from the benchmark solutions obtained in a static environment for the same geometry. The physical reasons for ampli#cation and weakening of sound are discussed in terms of dynamics of wave pro#le and redistribution of acoustic energy and its potential and kinetic components. For an acoustic wave in the #ow around a cylinder, the observed mean acoustic pressure is approximately doubled #upstream pulse position# and halved #downstream pulse position# in comparison with the sound propagation in static ambient conditions