Effects of source convection on vortex sound

The amplification of vortex sound due to the source convection is numerically investigated in this paper. To this aim, the dynamics of two axisymmetric vortex filaments is computed for different values of the vortex circulation and the convection velocity. According to Lighthill's acoustic analogy, the unsteady flow field provides the source term of a nonhomogeneous wave equation: this is integrated using a Green's function approach, to obtain the acoustic pressure. In order to understand how the convection affects sound emission, different formulations have been used to evaluate the convolution integral. Results obtained at different convection velocities show that an amplification of the sound radiated in the forward direction is observed as long as the difference in retarded times of the source is accounted for.