Computational study of tip-leakage flow around a static hydrofoil

The flow field in the tip gap region between a rotating blade and a static casing is commonly referred to as tip-leakage flow (TLF). This flow is observed in many fluid mechanics applications such as axial turbomachinery and ducted propulsors. TLF features complex vortical structures with a high susceptibility to cavitation inception in water. The present work adopts the Reynolds-Averaged Navier-Stokes (RANS) equations, solved using ANSYS Fluent, to simulate the TLF of a static hydrofoil at a Reynolds number of 3×106. This configuration was recently studied experimentally at the Australian Maritime College Cavitation Research Laboratory for tip gap spacing between 3.36 ∼ 53.8 mm (0.1 to 1.6 times the maximum hydrofoil thickness). The objective of this study was to resolve the different vortices that exist within the TLF and accurately predict their minimum pressures, which is an important parameter for cavitation inception prediction. Computational fluid dynamics (CFD) simulations matched the experimental conditions, with the hydrofoil chord at an incidence angle of 6 degrees to the freestream flow and the same ceiling (casing) boundary layer thickness as in the experiment. Single-phase computations were carried out to assess the performance of different numerical configurations e.g. eddy viscosity and Reynolds stress turbulence models, wall resolved and wall functions, and grid resolution. Despite cell counts approaching 500 million, grid convergence of the simulations was not achieved with the predicted minimum vortex pressure still decreasing with grid refinement. However, comparison of the predicted tip-leakage vortex trajectory, and the predicted region where the static pressure fell below the vapour pressure, showed good agreement with observed cavitation regions from the experiments.