Suppressing tip vortex cavitation through passive deformation of a hydrofoil. II. Twisting

In this paper, we investigate geometric twisting as a passive control strategy to mitigate tip vortex cavitation (TVC) in marine propellers and hydrofoils. Large eddy simulation of tip vortex flow past an elliptical NACA (National Advisory Committee for Aeronautics) 66(2)-415 hydrofoil in various twisting configurations is conducted in non-cavitating and cavitating conditions. Twisting is parameterized by the twisting span and tip-twisting angle, and a variety of twisting configurations are investigated. The configurations include quarter-, half-, and full-span twisting with tip-twisting angles ranging from −9° to 9°. An analysis of tip vortex core pressure in non-cavitating conditions and tip vortex cavity in cavitating conditions reveals the potential of geometric twisting by positive tip-twisting angles in alleviating TVC. To ensure practicality, the effect of twisting on hydrodynamic performance is evaluated. Partial-span twisting with positive tip-twisting angles leads to no adverse impact, or even a slight improvement, in hydrodynamic performance. Examining the integrated performance index indicates improved performance in twisted cases with positive tip-twisting angles, considering both hydrodynamic performance and TVC intensity simultaneously. A detailed investigation of the flow field reveals that the variations in the spanwise loading distribution, tip vortex–wake interactions, and boundary layer behavior are the major mechanisms involved in TVC mitigation achieved by twisting. The findings demonstrate geometric twisting as an effective and practical TVC mitigation strategy for hydrofoils and marine propellers, which offers suppression of cavitation without compromising and potentially improving hydrodynamic performance.