Characteristics and mechanisms of the tip leakage cavitating flow around a NACA66(mod) hydrofoil under different cavitation states

The purpose of the present study is to shed light on the characteristics and mechanisms of tip leakage cavitating flow under different cavitation states, especially for the tip leakage vortex (TLV) and tip leakage vortex cavity (TLVC). The large-eddy simulation and a newly proposed Burgers vortex cavitation model have been used for the numerical simulations. Three modes of TLV have been summarized according to the development features of the TLV circulation Γ with different cavitation states. At the ascending stage, Mode I has 30.5% and 229.5% more averaged values of Γ than Mode II and Mode III, respectively. However, at the declining stage, the averaged values of Γ for Mode I are 33.2% and 1461.3% larger than those of Mode II and Mode III, respectively. Detailed analysis of the relative axial velocity and the pressure gradient in the TLV core shows that the adverse pressure gradient has a huge effect on the stability of the TLVC. The interaction between the cavitation and vortex was investigated by using the vorticity transport equation. It is found that stretching and dilatation terms are the most critical factors during the development of the TLVC, however, they play different roles in different positions.