Numerical investigation into the effects of tip vortex cavitation on propeller underwater radiated noise (URN) using a hybrid CFD method

Abstract

This study explores the influence of tip vortex cavitation (TVC) on propeller induced URN using a hybrid CFD method. The cavitating flow around the model and full-scale benchmark propeller belong to the Newcastle University's research vessel, The Princess Royal, operating under uniform, inclined and non-uniform flow conditions were solved using DES and mass transfer model. The recently developed advanced mesh refinement (V-AMR) technique was incorporated into the calculations for better modelling tip vortex flow and realising the TVC in the propeller slipstream. This technique enabled the inclusion of the nonlinear noise sources, mainly represented by turbulence and vorticity, including TVC, effectively for the accurate prediction of propeller URN. The numerical calculations were conducted in conditions where only the sheet cavitation was modelled without the V-AMR technique and where the sheet and tip vortex cavitation was modelled together using the V-AMR technique to understand the contribution of TVC to the overall propeller URN. The results were first validated with the available experimental data obtained in the model scale test campaign in the cavitation tunnel and sea-trial data for the propeller's hydrodynamic performance characteristics, cavitation extensions and URN. The results showed that the contribution of TVC to the overall propeller URN was minimal in conditions where the stable and structured TVC was present (i.e., under uniform flow conditions). However, when the propeller was operating under inclined and non-uniform flow conditions where the cavitation dynamics and vortex pulsation were dominant, the unstructured and unstable TVC was observed compared to the observations of TVC under uniform flow conditions. The unstructured TVC created several spikes, which can be associated with its strong cavitation dynamics and possible collapsing/bursting phenomena. These spikes created by the TVC and observed in the time domain acoustic pressure signal consequently contributed to the propeller URN at the different frequency ranges of the noise spectrum and increased the URN levels up to 15 dB under non-uniform flow conditions compared to the propeller URN predictions when only the sheet cavitation was present.