The sound field due to an elliptic cylinder in rectilinear motion

The sound field induced by a cylinder moving perpendicular to its length in an inviscid, compressible fluid is determined. The cylinder has elliptic cross section with semimajor axis a-prime and its velocity, characterized by U0, varies on the timescale t0 = a-prime/U0 and is small compared with c0, the mean sound speed in the fluid. It is also assumed that a-prime is very much less than c0t0, a characteristic wavelength, so that the cylinder is compact. By using a modified matching argument, an asymptotic solution for the velocity potential is obtained. In particular, the acoustic field at distances much greater than a-prime is described in terms of moving line source and multipole potentials whose singularities lie at the center of the cylinder.