Numerical investigation of the effects of free surface on tip-leakage vortex cavitation behaviors over a NACA0009 hydrofoil

Tip-leakage vortex (TLV) cavitation is complex and challenging multiphase flow problem in propulsion equipment. In this paper, the large-eddy method and the Schnerr-Sauer cavitation model are combined to simulate a NACA0 0 09 hydrofoil near the free surface. The numerical method used is validated by comparing the characteristics of TLV cavitation with available experimental data. The results show that the free surface affects the evolution of the cavitation and the characteristics of the hydrodynamic load. The lift and drag coefficient of the TLV hydrofoil decreases for the near free surface case, but the pulsation frequency of the lift coefficient increases. Meanwhile, the mechanism of the TLV near the free surface is found by comparing that case to a no free surface scenario. Moreover, an improved dynamic mode decomposition (DMD) method is used to investigate the unsteady cavitation flow characteristic of the TLV. The results show the main flow features of the TLV cavitation including the coherent structure and energy distribution are closely related to the existence of free surfaces by analyzing the first two modes based on the DMD method. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study combines the large-eddy method and the Schnerr-Sauer cavitation model to investigate the complex multiphase flow phenomenon of TLV cavitation near the free surface. The research shows that the free surface affects the evolution of cavitation and the characteristics of hydrodynamic load, and an improved dynamic mode decomposition method is used to analyze the unsteady flow characteristics of TLV cavitation.