Acoustic analysis of a forced-oscillating cylinder in flow using a hybrid method

Abstract

An acoustic analysis based on a hybrid methodology is performed for a transversely forced-oscillating circular cylinder with the aim of understanding the sound generation mechanism. The sound is predicted both in moving-observer and moving-medium systems using the unsteady near-field flow solutions as input. Different forms of integration formulation, the effect of placement of the data surface, the impact of surface closure and averaging among various closed surfaces are investigated over a range of F=0.2 to 1.4 where F is the frequency ratio of cylinder oscillation to the natural vortex shedding frequency. The results show that the sound is mainly radiated from the cylinder surface, induced by the unsteady aerodynamic loading and cylinder movement. The impact of the hydrodynamic structures of the cylinder wake on the predicted sound signal varies in different regimes of F. For 0.2≤F≤0.7, the hydrodynamic perturbation introduces spurious noise sources on the intersecting portion of the permeable data surface. For 0.8≤F≤1.05, the mean flow of the wake affects sound propagation through a convective effect, which must be taken into account in hybrid prediction. For 1.1≤F≤1.4, the effect of the wake flow on the sound generation, propagation and prediction is small. The accuracy of hybrid prediction can be significantly improved by both the open permeable surface and surface-averaging.