Abstract
Methods to predict underwater acoustics are gaining increased significance, as the propulsion industry is required to confirm noise spectrum limits, for instance in compliance with classification society rules. Propeller–ship interaction is a main contributing factor to the underwater noise emissions by a vessel, demanding improved methods for both hydrodynamic and high-quality noise prediction. Implicit large eddy simulation applying volume-of-fluid phase modeling with the Schnerr-Sauer cavitation model is confirmed to be a capable tool for propeller cavitation simulation in part 1. In this part, the near field sound pressure of the hydrodynamic solution of the finite volume method is examined. The sound level spectra for free-running propeller test cases and pressure pulses on the hull for propellers under behind ship conditions are compared with the experimental measurements. For a propeller-free running case with priory mesh refinement in regions of high vorticity to improve the tip vortex cavity representation, good agreement is reached with respect to the spectral signature. For behind ship cases without additional refinements, partial agreement was achieved for the incompressible hull pressure fluctuations. Thus, meshing strategies require improvements for this approach to be widely applicable in an industrial environment, especially for non-uniform propeller inflow.
Highlights
The rapid growth of shipping activities in the last century has created a substantial increase in anthropogenic noise in the oceans
We report an industry-oriented feasibility study of an Implicit large eddy simulation (ILES)-based numerical noise evaluation method, by analyzing the near-field acoustic emissions of two free-running propellers and their induced turbulence in the propeller slipstream, with one applying a vorticity-based a priori mesh refinement
There is the round robin test measurements of University of Genoa (UNIGE) [22], while the same simulation was performed in a quasiinfinite domain by SINTEF Ocean, conducted with STAR-CCM+ and LES with a standard
Summary
The rapid growth of shipping activities in the last century has created a substantial increase in anthropogenic noise in the oceans. The underwater background noise levels have intensified by up to 3 dB per decade in specific frequency bands in some regions [1], which could be a source of deleterious effects on marine biology [2,3], especially when considering the comparatively short timescale of the transformation and the long lifespan of some species, such as cetaceans or testudines. Integrated behind a ship, the turbulence and cavitation is strongly affected by the non-uniform inflow, which creates unsteady vortex structures and fluctuating cavity regions with respect to a blade’s fixed coordinate system. Underwater sound emission is a direct effect of the propeller’s operation in the vessel’s wake field and several interactions with the ship’s hull, as well as increased cavitation with higher vessel speeds, for which not all mechanisms are fully understood [7]. Contemporary propeller designs often purposefully allow for non-erosive cavitation patterns to reach higher efficiencies, which are primarily stable sheet cavitation fluctuating only with reductions in inflow velocity in the wake field and tip vortex cavitation, which is the main contributor to volume-based sound sources in the propeller slipstream [8]
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