Exploring cloud cavitation and cavitation vortex dynamics with partially averaged Navier–Stokes turbulence models

Cavitation occurs due to low static pressures, which generally develop from high Reynolds number flow conditions. Cavitation can lead to the development of an unstable flow state. One such regime is cloud cavitation for flow over hydrofoil. Investigation of cavitation formation, its propagation mechanisms and mitigation are, thus, necessary for achieving a stable flow condition for hydrofoil. This paper investigates cavitation flow over hydrofoil numerically. The cost-effective and improved Partial Averaged Navier–Stokes turbulence model is used. In PANS simulation, an implicit filter called fk is introduced and adjusted to represent the ratio of unresolved (ku) to resolved (k) turbulent kinetic energies. The simulations are performed for a range of filter parameters (1 ≤fk≤ 0.5) to resolve the turbulent flow. The study is conducted at an angle of attack of 3° and a cavitation number of 0.9, which facilitates the formation of cloud cavitation. This turbulence model eliminates turbulent viscosity overprediction in the cavity area near the trailing edge (TE) when the resolution parameter is lowered to fk = 0.5. Compared to experimental results, fk = 0.5 closely matches the maximum cavity length (1.87%) and time period (0.2%). Further, cavitation vortex dynamics is discussed, and it is observed that vortex starching (ω→·∇)V→, vortex dilation ω→(∇·V→), and baroclinic torque (∇ρm×∇pρm2) are the main factors that alter the vortical flow generated due to cavitation at hydrofoil suction surface and downstream of TE. Finally, dynamic mode decomposition is applied to the vorticity field to find the dominant coherent structures. Strouhal number of Mode 2 (0.124) is near to cloud shedding (0.121).