Influence of the tip gap size on the development of the tip-leakage vortex using Large Eddy Simulations

etc15 Tracking Number 39

In hydraulic turbines, the tip-leakage vortex is responsible for flow instabilities and for promoting erosion due to cavitation. To better understand the flow in the tip region, LES computations are carried out to compute the flow around a NACA0009 blade including the gap between the tip and the wall. The influence of the gap size is investigated by computing two gap widths. The validation of the results is performed by comparisons with experimental data. The simulations are also used to investigate the flow in the tip gap region. Depending on the gap width, the vortex flow topology differs from one case to the other. At large gap widths, the tip-leakage vortex merges with the tip-separation vortex. On the contrary, at small gap widths, the tip-leakage vortex move upward and no tip-separation vortex is clearly identified. Part of these observations are validated by comparisons with experimental visualizations of the cavitating tip-leakage vortex.