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Computational studies of the flow around rounded and ducted tip hydrofoils Ingvarsdottir, Hildur

Abstract

All lifting surfaces that terminate in a moving fluid create tip vortices. Tip vortices on marine propellers reduce the efficiency of the blades and can cause cavitation. Cavitation is an undesirable effect since it can cause pitting and erosion of the propeller and surrounding equipment and is a source of vibration and noise. Several tip devices have been proposed to suppress the tip vortex roll-up and reduce the strength of the tip vortices. One of those is a flow-through duct installed at the tip of a propeller blade. In this research the flow over ducted and rounded tip hydrofoils was studied using the finite-volume flow solver CFD-ACE(U) and a k-e turbulence model. First the flow over two rounded tip hydrofoils, which were selected based on experimental data available, was studied with validation in mind. It was shown that away from the tip of the hydrofoil the sectional lift was predicted within 2% of experimental data whereas close to the tip the difference in lift reached up to 12%. The spanwise location of the vortex core was shown to be well predicted. This study was followed by studying the flow over a ducted tip hydrofoil. For comparative purposes a rounded tip hydrofoil of the same cross-section and aspect ratio run under the same flow conditions was studied. A good agreement in flow pattern was achieved between the computational results and available experimental data. A good agreement was also achieved between the maximum axial and tangential velocity immediately downstream of the hydrofoil. The computations showed that the ducted tip hydrofoil sheds less bound circulation over the majority of the wing span than does the rounded tip hydrofoil. The tip vortex from the ducted tip hydrofoil is shed in the shape of a duct instead of a concentrated circular vortex from the rounded tip hydrofoil.

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