Nuclei content effects on cavitation inception noise predictions using viscous CFD and Lagrangian bubble tracking

Cavitation inception noise, particularly for tip vortex cavitaiton, forms an important part of ship acoustic signature that affects detectibility thresholds of vessels and indicates the onset of erosion risk. Numerical modelling of this phenomenon using Eulerian models is challenging due to the need to resolve very small bubble radii of the order of tens of micrometres on a grid encompassing a propeller blade or a model-scale hydrofoil. This work proposes a Lagrangian bubble tracking approach coupled with a viscous CFD code, ReFRESCO, that allows the onset of acoustic cavitation to be predicted. The model is validated with published experimental data for an elliptical foil, showing satisfactory agreement in terms of absolute noise levels as well as accurate reproduction of the noise spectrum shape. Several sensitivity studies are later undertaken with the aim of quantifying the importance of bubble size distribution spectrum, ambient volume fraction, and cavitation number on the radiated noise levels. It is shown that all of the aforementioned parameters can have substantial influence on the radiated noise. This highlights the need for accurate validation data, including detailed nuclei measurements, for future studies, but also stresses the extreme difficulties in accurate scaling of model-scale cavitation inception noise results to full scale ships operating across a wide range of conditions.