Characterisation of sheet cavity noise of a hydrofoil using the Ffowcs Williams Hawkings acoustic analogy
Abstract Concerns about pollution of the marine environment with ship induced noise and the scarcity of available numerical methods have recently stimulated significant amounts of research in hydroacoustic modelling. In this work, Large Eddy Simulation (LES) is used with Schnerr Sauer mass transfer cavitation model and a porous Ffowcs Williams Hawkings (FW H) acoustic analogy in order to simulate sheet cavitation on a NACA0009 hydrofoil. The aim is to investigate how well the proposed method captures the dominant noise sources associated with periodic sheet cavitation. The study further focuses on practical aspects, such as the importance of the non linear FW H term and convergence of the acoustic solution depending on the choice of the integration surface. This is done by correlating the radiated noise with integral and local flow quantities, such as cavity volume, lift coefficient and local vapour content. A key finding of the study is that the simulation framework is capable of correctly capturing the monopole nature of the sound generated by an oscillating cavity sheet. Results indicate that the numerical method is incapable of accurately resolving the flow during the final collapse stages of smaller cavity clouds, mainly due to mesh density limitations and the use of an incompressible flow assumption. Lack of small scale bubble structures also causes the high frequency range of the noise spectra to be under predicted. Despite certain limitations the presented method offers a significant insight into the nature of cavitation dominated noise and allows for some of the dominant sound generating mechanisms to be categorised.