Investigation of unsteady cavitating flow around a hydrofoil using GAS method

Cavitation significantly impacts the performance of hydraulic machinery. However, cavitation is complex, and the evolution of complex vortical structures in cavitating flow requires further investigation. In this study, the unsteady cavitating flow around a NACA0009 hydrofoil with gap sizes of 1 and 10 mm is simulated using grid-adaptive simulation (GAS), which is a novel hybrid method that modifies the turbulent viscosity based on the Kolmogorov energy spectrum. The prediction accuracy of GAS is validated by comparing with experimental and LES results, demonstrating its superiority compared to the scale-adaptive simulation. A detailed study on the effect of gap size with an emphasis on the evolution of complex vortical structures is performed. It is discovered that the gap size plays a crucial role in the development of complex flow structures, as well as their interactions. Moreover, as the gap size increases, the two-layer structure of tip leakage vortex (TLV) becomes more pronounced. The inner TLV core region is generated by the vorticity transport from tip to the TLV. The outer layer structure is formed by the mainstream, tip separation vortex and leakage flow. The complex outer layer significantly influences the stability of the TLV and cavities. The investigation on the TLV structure in this study of cavitation flow aligns with the previous conclusions in compressors, indicating that two-layer structure of the TLV is a universal phenomenon.