Numerical investigation of tip leakage vortex cavitation

Tip leakage vortex cavitation is a concern for axial hydraulic turbines. Generally, cavitation may occur in the core of the TLV, often leading to erosion of the runner blades and the casing. The objective of this paper is to study the effects of this phenomenon on the hydrodynamics characteristics of a standard NACA0009 blade. Numerical simulations of the present study are carried out using the ANSYS CFX. The k–ω SST turbulence model and the Schnerr-Sauer cavitation model are respectively used for the modeling of turbulence and cavitation. In the first step of this study, the effect of considering cavitation phenomenon and transient state is investigated by monitoring the coordinate of the vortex core center and comparing them with the experimental data. The steady state simulation with cavitation modeling leads to acceptable prediction of vortex core center position and the unsteady cavitation modeling further improved the accuracy of the predictions. The influence of tip clearance, incidence angle and cavitation number on the hydrodynamics characteristics of the hydrofoil is further studied. The results demonstrate that incidence angle and cavitation number have more pronounced effects on improving the lift to drag ratio in comparison to the tip clearance. According to performance curves, the maximum lift coefficient is obtained by incidence angle of 12 degree in the cavitation number range of 1<σ<1.25. (paper)