A novel flow control method suppressing tip leakage vortex of a hydrofoil applied for ducted devices

In bladed energy conversion machines, the tip leakage vortex (TLV) is a prevalent phenomenon, which can lead to both flow losses and cavitation. Numerous scholars in recent years have proposed effective methods for TLV suppression, utilizing either active or passive control strategies. This work focuses on the implementation of the hole-pit (HP) structure located at the leading edge 2%-25% chord position of the hydrofoil to induce passive jets and separate flows for suppressing TLV structures. The rotating curvature correction (CC) shear stress transport (SST) k-omega turbulence model and Zwart-Gerber-Belamri (ZGB) cavitation model are employed to clarify the control effect and mechanism of HP structure through numerical analysis and experimental verification. The results reveal that the passive jet and pit-separated flow from the HP structures effectively divide the TLV into distinct segments, giving rise to new vortical structures. These vortical structures are categorized hole separation vortex (HSV), pit separation vortex (PSV), newborn tip separation vortex (NTSV), and weakened tip leakage vortex (WTLV). The control ability of HP structures in different schemes is strongly correlated with their number and arrangement. Optimal control effects are achieved when the HP is positioned near the separation vortex over the top of the foil. Specifically, when the number of drainage holes is 3 or 4, the theoretical TLV cavitation length is suppressed by at least 63.93%. The passive jet induced by the HP structure alters the distribution of different kinds of energy losses in tip clearance and TLV core through the effect gap leakage flow, leading to a sharp rise in the value of total energy loss. This results in a weakening of gap leakage flow energy and TLV intensity, accompanied by a raised vortex core pressure. Thus, the research successfully realizes the purpose of suppressing both TLV and TLV cavitation.