Numerical investigation of multistage cavity shedding around a cavitating hydrofoil based on different turbulence models

Multistage shedding in cavity flow processes is a challenging and crucial topic in cavitating flows. This paper employs three different turbulence models to obtain a more comprehensive understanding of the physical details of multistage shedding in compressible cavitating flows and compare the differences between the turbulence models. The study employs the Schnerr-Sauer cavitation model in combination with the volume of fluid (VOF) method to capture the details of the unsteady cavitating flow around NACA66. The results are compared to experimental data and validate the numerical method. The study reveals that the primary shedding process is dominated by the re-entrant jet mechanism, whereas the pressure wave mechanism dominates the second shedding process. The second shedding process generates multiple pressure waves that disrupt the stable vortex structure of the sheet cavity. Furthermore, wavelet analysis indicates that the higher-order coherent structure mainly originates from the second shedding stage, and the second shedding process is shorter than the primary shedding process. The study proposes the segmented dynamic mode decomposition (SDMD), which obtains the mode characteristics at different time scales within one cycle. Under the RANS model, the small-scale cavity collapse and vortex structure cannot be observed during the second shedding process. However, the LES model can predict more realistic multi-scale flow field information.