Sound radiation from the motion of point vortices outside a circular cylinder at low Mach number

Sound radiation due to the unsteady motion of point vortices in incompressi ble ideal fluid outside a circular cylinder is analyzed using the asymptoti c matching technique and the mirror method. It is found that when three or more point vortices distribute evenly in a concentric circular orbit around the cylinder, the outer-field sound radiation caused by the motion of thes e vortices will nearly disappear. This new discovery is of great significan ce for the vortex noise control and the development of the acoustic stealth theory.