LES Analysis of Vortex-Vortex Interaction and Associated Acoustic Signatures

Abstract The rising levels of underwater ambient noise due to shipping have attracted the attention of international bodies such as the International Maritime Organization (IMO), International Towing Tank Committee (ITTC) and Vancouver Port, who aim to minimise radiated noise and reduce impact on marine creatures. A high-intensity turbulent noise not only brings negative impacts on a ship’s silent operation but also contributes to noise pollution that can disturb marine animals. Reconnection and breakdown of coherent vortices in propellers’ wake can produce significant pressure fluctuations, intensifying turbulent energy and contributing to a distinct noise signature. Relatively few studies have investigated the specific acoustic signatures resulting from vortex-vortex interactions. This study aims to understand these interactions and their associated acoustic signatures for a Vortex Reynold number, approximately of 2700, by examining the corresponding far-field acoustic signatures generated by these interactions. Contra-rotating and Co-rotating parallel vortex pairings with different separate distances under the same axial velocity had been modelled. These were conducted using Computational Fluid Dynamics (CFD) methods, where Large Eddy Simulation (LES) in combination with the Ffowcs Williams-Hawkings acoustic analogy (FW-H) were used to solve the hydrodynamic flow field and propagation of associated noises to the far-field. The unique acoustic signatures and hydrodynamic characteristics obtained from this investigation can provide an alternative perspective for understanding underwater acoustics, vortex-vortex interactions, and instabilities in incompressible conditions.