Effect of vortex profile on sound generation in a non-uniform flow Original Research Article

Propagation of acoustic waves caused by deformation of self-similar vortices in the non-uniform flow is studied by numerical modeling using high-order compact approximation. Since the profile of shedding vortices may vary dramatically, zero-circulation Taylor vortex model and non-zero circulation Vatistas vortex model were considered to compare generated acoustic waves. Stagnation flow at flat plate (case A) and flow around non-rotating rigid cylinder (case B) are taken as prototypes of real-world flows with strong gradients of mean pressure and velocity. Near-wall deformation of initial vortex by the stagnation flow leads to sound radiation from the generated pressure quadrupole. Gradually decaying velocity profile of the Vatistas vortex creates substantially wider pressure quadrupole than that for the Taylor vortex. As a result, both the amplitude and sector of influence for acoustic waves coming out of the Vatistas vortex are larger than those for the Taylor vortex. For case B, two various vortex core sizes were considered: (a) the vortex core diameter is much smaller than the rigid cylinder diameter, and (b) the vortex core size is comparable with the cylinder diameter. The influence of relative vortex core diameter on the directivity of wave propagation has been investigated for both Taylor and Vatistas profiles. Generation of sound by deformation of vorticity dipole leads to formation of a three-spot wave with maximum acoustic pressure at the centerline. In this case, mutual cancellation of waves weakens the influence of vorticity profile and core size on the amplitude and directivity of acoustic waves.