A high-fidelity discontinuous Galerkin modeling framework for underwater acoustic propagation.

Anthropogenic noise from marine shipping and other sources poses a serious threat to marine mammals and the ocean environment. The formation and collapse of bubbles during propeller-induced cavitation is the dominant source of underwater sound produced by ships.  This work explores the physics of noise emission from deforming geometries in turbulent and multiphase flows by developing a coupled framework for flow and acoustic simulation. We are particularly interested to understand how cavitation impacts noise radiation with varying parameters.  Acoustic propagation is simulated by solving the linearized Euler equations via the discontinuous Galerkin finite element method. The acoustic solver is one way coupled to the multiphase fluid-structure interaction solver by extracting the time history of hydrodynamic pressure and density as acoustic sources. Interpolation between non-matching flow and acoustic grids is implemented to take advantage of different length scales between flow and acoustic phenomena. The acoustic solver is first validated against analytical solutions for acoustic monopole and dipole sources. The combined flow-acoustic hybrid framework is validated through the sound generation of a vortex shedding 2D cylinder at a laminar flow with Re=200. Finally, the framework is demonstrated through sound generation by a cavitating airfoil.