Research on the suppression mechanism of a tip leakage vortex over a hydrofoil with double-control-hole structure

Abstract

Tip leakage vortex (TLV) usually exists at a small tip clearance in axial-flow energy conversion machines, which may induce flow loss, vibration, noise and vortex cavitation. In this work, the double-control-hole (DC hole) at the leading edge of a hydrofoil is used to suppress TLV by inducing a passive jet. The SST-CC model by adding a rotation-curvature correction (CC) term into the original shear stress transport (SST) k-ω and Zwart-Gerber-Belamri (ZGB) model were applied to investigate the controlling effect under different Reynolds numbers (Re). The results show that TLV is decomposed and new vortices are generated when changing Re. By guiding the high-pressure flow from the pressure side (PS) to the suction side (SS) of hydrofoil vertically, the TLV core pressure is increased and local cavitation is suppressed. When the inflow velocity gradually increases to 7.5 m/s, 10 m/s and 12.5 m/s, the velocity swirl intensity at the TLV core is suppressed by nearly 50%, 36.4% and 28%, respectively, showing a downward trend. Based on the vorticity equation, it is observed that the distribution of TLV vortex bending terms is changed. Also, the vortex bending term and the vortex stretching term are suppressed in specific directions. Further analysis of the suppression mechanism of DC hole indicates that this structure can increase the turbulent kinetic energy of TLV, which destabilizes the flow field. Besides, the velocity circulation in the downstream region of TLV can be reduced, which can suppress the TLV effectively.