Numerical study on the influence of boundary-layer thickness on tip-leakage flow for a hydrofoil

Abstract: This study numerically analyses the influence of boundary layer (BL) thickness on the tip-leakage flow for a stationary hydrofoil, presenting the effectiveness of computational predictions. The commercially available computational fluid dynamics (CFD) package Simcenter STAR-CCM+ 2302, which employs a finite-volume method solver, was adopted for the simulations. The shear stress transport (SST) turbulence model was adopted, and steady simulations were performed to evolve the computations. The distinct BL thicknesses were simulated by adjusting the boundary condition on the inlet of the computational domain. The computed trajectories of the tip-leakage vortex (TLV) agreed with those obtained in the experiment (Russell et al., 2024). The leakage flow (transverse flow in the tip clearance) became more significant with decreasing the tip gap, supporting the shift of the TLV away from the hydrofoil suction face. The incipient cavitation numbers predicted with CFD for the thicker BL (δ99 = 70 mm) were smaller than those for the thinner BL (δ99 = 30 mm), which was consistent with the decreased cavitation event rates with increasing BL thickness reported in the experiment. A high turbulence region extended downwards for the thicker BL, and more significant interactions of the TLV with the BL flow yielded. The higher ambient turbulence and interactions with the BL flow induced fluctuations of the TLV trajectories for the thicker BL and increased the pressure near the vortex core due to the interruption of the TLV coherence. Keywords: tip-leakage flow, boundary-layer thickness, CFD