Numerical analysis on the system instability of the cavitating flow around hydrofoil induced by the non-uniform inflow

One common type of system instabilities of partial cavitation, induced by the non-uniform inflow, was numerically investigated in the present study. Large eddy simulation (LES) method coupled with Zwart-Gerber-Belamri cavitation model and volume of fraction (VOF) are used to capture the unsteady cavitating flow around NACA66. Unlike the intrinsic instabilities caused by the cavity itself, the occurrence of system instabilities is usually accompanied by the intrinsic instabilities. Therefore, it is their nonlinear interaction that makes analyzing the system instabilities separately quite difficult. By comparing the effects of the uniform and non-uniform inflow on the cavitating flow as well as the non-cavitating flow, the influences of the system instability induced by the nonuniform inflow on the partial cavitation are analyzed tentatively. The results show that the non-uniform inflow has little effect on the cavity shape evolution, but makes the dominant frequency caused by the shedding behaviors of the cavities higher. In contrast, the non-uniform inflow significantly changes the mean velocity profile in the cavitation regions near the foil wall especially over the front part of the foil (x/C<0.5). Besides, it also makes the maximum values of the Reynolds shear stress <uv> smaller, and its normal locations closer to the foil wall. By the continuous wavelet analysis, it is observed that the large-scale coherent structures containing relatively high energy are mainly generated during the collapse stage of the cavities. The non-uniform carrier fluid may induce more large-scale coherent structures during this stage. By the discrete wavelet transform, the energy of the non-uniform cavitating flow has a more complex distribution at the expense of the energy for the large and moderate scales.