A computational aeroacoustics technique is developed and applied to analyze the acoustic fields generated by unsteady incompressible vortical flows. Acoustic equations are derived from the unsteady Euler equations by splitting into hydrodynamic and acoustic terms. The hydrodynamic pressure fluctuations of unsteady vortical flow fields are thermodynamically related to the hydrodynamic density fluctuations, which are acting as the sound source.
A spinning vortex-pair is adopted to represent a quadrupole sound source which can be expressed as a divergence of the motion of the vorticity. MacCormack's explicit predictor-corrector scheme is used to calculate the time-dependent acoustic fields. A non-reflecting boundary conditions are developed and proved to be successful.
Acoustic fields generated by the flow fields of a spinning vortex-pair are calculated and compared with analytical solutions. A spinning vortex-pair as a quadrupole source in the presence of an infinite flat-plate wall are also studied and the effects of the wall dipole are analyzed. Finally, the acoustic analysis code is converted into the generalized curvilinear coordinates system, and the acoustic fields generated from a quadrupole source and scattered by a circular cylinder are calculated. It is expected that present study can be applied to more general acoustic fields from general unsteady vortical flows interacting with bodies.
