A NUMERICAL EVALUATION OF VISCOUS EFFECTS ON VORTEX-INDUCED NOISE

The effect of viscosity on the noise generated by interactions of simp le axisymmetric vorticity structures is numerically investigated. A lo w Mach number is assumed, and hence the feedback of the acoustic held on the flow can be neglected. With this assumption, Lighthill's acoust ic analogy enables one to determine the farfield pressure perturbation due to vorticity motion. For a swirl-free incompressible flow, numeri cal simulations are performed with a finite difference scheme in terms of the vorticity and the stream function. The acoustics of collision and pairing of vortex rings is investigated for growing Reynolds numbe rs. Results show that the quadrupole term converges to the inviscid on e, while the acoustic term due to the energy dissipation vanishes, acc ording to the theoretical prediction of Obermeier. (C) 1996 Academic P ress Limited