Sound generation by vortical disturbance in a subsonic flow around a cylinder is investigated, using different vortex formulations, by solving both linearized and nonlinear Euler equations numerically. Numerical errors associated with the finite-difference discretization and boundary conditions are kept small using the high-order-accurate spatial differentiation and time marching schemes along with accurate nonreflecting boundary conditions and the sponge layer. If the radial velocity in vortex is assumed equal to zero, the intensity and directivity of acoustic wave patterns appear to be quite similar for all vortex models. If the radial velocity is taken into consideration, for single-cell vortex, there is no noticeable change happening to the acoustic wave; for two-cell vortex, although the radial velocity is still much smaller than the tangential velocity, the former plays an important role in generation and propagation of nonsymmetrical sound waves. If only initial tangential velocity or only initial radial velocity of the two-cell vortical flow disturbance is considered, the generated sound level would increase with the Mach number of mean flow while the angular distribution of sound directivity remains the same. If the two-cell vortex with both velocity components is considered, the Mach number of the background flow would change not only the amplitude of the acoustic pressure but also the directivity of sound. As the Mach number increases, the maximum amplitude of acoustic pressure will be shifted to the upper half-plane.
