Large Eddy Simulation of the transient cavitating vortical flow in the wake of a hydrofoil

Abstract

The Zwart mixture cavitation model and the Large Eddy Simulation (LES) turbulence model have been combined to simulate the transient cavitating flow in the wake of a hydrofoil. The hydrofoil is a 2D NACA0009 with a truncated trailing edge which has been extensively investigated experimentally in the EPFL high-speed cavitation tunnel. The simulated flow conditions correspond to a free stream velocity of 20 m/s (Re = 2 × 106) and an incidence angle of 0° for different levels of cavitation number, ¿¿, ranging from free cavitation to cavitation flow with different amounts of vapor. Under such hydrodynamic conditions and blunt trailing edge geometry, a Von Kármán vortex street takes place that is the object of the present study in order to ascertain how cavitation modifies the vortex structure and its dynamic behavior. The numerical results show a good agreement with the experimentally measured vortex shedding frequency without and with cavitation. As observed experimentally, the numerical results also predict an increase of the frequency induced by a significant change of the vortex properties. In order to identify the effects induced by the occurrence and development of cavitation, the obtained unsteady velocity field has been analyzed via Proper Orthogonal Decomposition (POD) technique to identify and understand changes in the flow structure. It has been found that the occurrence and development of cavitation can change the contribution of the POD modes to the total velocity filed. Moreover, the appearance of cavitation seems to stabilize the flow field unsteady behavior since high order POD modes are harmonically correlated with the first couple of basic POD modes.