Abstract
Ducted propellers are expected to provide significant hydrodynamic and hydracoustic benefits for underwater vehicles. However, ducted propellers typically have a tip gap between the blades and duct surface, which can cause flow instabilities and cavitation resulting in undesirable noise. Therefore, understanding the tip-gap flow mechanism is critical for managing the hydroacoustics of these propulsors. This study focused on a fundamental analysis of a tip-gap flow of a hydrofoil using computational fluid dynamics. The Reynolds-averaged Navier-Stokes (RANS) turbulence model was primarily used to compute the mean global features of the tip-gap vortices, whereas a large-eddy simulation (LES) was used to resolve the crucial turbulent structures. A mesh refinement study was performed by decreasing the mesh size in the tip-gap region. The computed vortex topology in the tip-gap region was similar to that obtained in an experiment. Further analysis of the tip-gap flow was conducted, and several remarks are discussed regarding the formations of tip-separation vortex, tip-leakage vortex, and induced vortex yielded. The LES computed the complex vortex structures, and the result was compared with that obtained with the RANS simulation.
