Sound radiation by a bubble encountering a vortex ring

Abstract

The dynamics of a bubble and subsequent acoustic radiation interacting with a vortex ring created by an underwater nozzle are studied both theoretically and experimentally. The velocity field of the flow containing the bubble may be represented as a ‘‘basic flow’’ related to the vortex ring and a ‘‘secondary flow’’ related to the bubble motion [G. Chahine, 20th Symposium on Naval Hydrodynamics (1994)]. The ‘‘bubble flow’’ is assumed to be irrotational satisfying the Laplace equation. The vortex related velocities are given by the stream function and are taken into account by imposing ‘‘correct’’ kinematics and dynamic boundary conditions at the bubble surface. The interaction of the bubble with a vortex ring has been shown to cause severe deformation. Under special circumstances the deformed bubble may be at resonance with these vortex filaments and force it to radiate sound to the far field. The boundary integral technique (BIT) is employed to solve governing equations. The BIT is utilized to simulate the ‘‘bubble flow,’’ its surface distortions and subsequent acoustic radiation. The critical parameters responsible for the acoustic re-excitation of the bubble encountering the vortex filaments are discussed in some details. Some conclusions are arrived at on the acoustical characteristics of the bubble encountering a fully developed turbulent flow field. [Work supported by ONR.]