<p>Cavitation is an ever-present issue within the maritime industry. It occurs due to a drop in local static pressure below the saturation pressure and this can cause efficiency loss, hull/shaft vibrations, blade erosion and increased underwater radiated noise (URN) levels. Along with cavitation, URN is also a key challenge within the maritime sector. URN has a detrimental impact on the acoustic marine environment utilized by numerous marine mammals to perform key biological functions. Due to this, the International Maritime Organization (IMO) published non-mandatory guidelines in 2014 to drive the reduction of ambient ocean noise levels. Typically, the propulsion system generates most of the URN from marine vessels, especially in cavitating conditions. Therefore, reducing the cavitation volume is key to reduce URN, increasing hydrodynamic efficiency and the propeller life at sea which will improve the acoustic marine environment and reduce the associated maintenance costs of cavitation-induced damage on the propeller. Ironically, a marine mammal that is affected by such URN, is the inspiration behind this research. The Humpback whale is an incredible marine mammal, performing agile movements to capture prey and this is made possible with the small bumps on the leading-edge of the pectoral fin known as leading-edge (LE) tubercles. This concept is the focus of many applications such as the aerofoil and the tidal turbine, where it has shown to improve hydro/aerodynamic performance in stall conditions, reduce noise and contain cavitation. This is due to the counter-rotating vortices that are produced by the sinusoidal pattern, creating a high-low pressure pattern from peak to trough, energising the boundary layer and encouraging flow attachment which would typically not be possible without such a feature. This paper assesses the cavitation containment capability of the LE tubercles on a benchmark marine propeller in both heavy-cavitating and near inception conditions over a range of operational conditions using commercial code STAR CCM+, Reynolds-averaged Navier Stokes solver and the Schnerr-Sauer cavitation model to quantify the sheet cavitation present over a range of operating conditions. As demonstrated in the simulations, in heavy-cavitating conditions, a reduction in sheet cavitation with the inclusion of LE tubercles was observed to a maximum value of 2.75%. This resulted in an improvement in propulsive thrust and efficiency in all operating conditions. This is because the LE tubercles disrupt the development of the cavitation, creating a fence-like structure and which results in a restriction of fully developed cavitation in the heavier-cavitating conditions.</p>

The Influence of Leading-Edge Tubercles on the Sheet Cavitation Development on a Benchmark Marine Propeller

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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