Parametric Study on Tip-Gap Flow of a Hydrofoil Using Computational Fluid Dynamics

Ducted propellers are expected to provide significant hydrodynamic and hydroacoustic 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. In this work, a parametric study on the tip-gap flow of a hydrofoil was performed using computational fluid dynamics. The tip-gap height, incident angle, Reynolds number, and section profile were the investigated parameters. The extensions of the tip-leakage vortex (TLV) and tip-separation vortex (TSV) decreased for smaller tip-gap heights. The isosurface of vapour pressure in the TLV was not observed for the largest tip-gap height, whereas it remained near the leading edge for the smallest tip-gap height. The TSV and TLV were mitigated for smaller incident angles, although a lower pressure region was yielded at the leading edge even for no incident angle. The global features of the TLV and TSV were similar for different Reynolds numbers. However, a greater leakage flow was observed for a higher Reynolds number. Enlarged TLVs and expanded lower pressure regions were observed for the thinner and cambered hydrofoils.