Numerical study on wetted and cavitating tip-vortical flows around an elliptical hydrofoil: Interplay of cavitation, vortices, and turbulence

Abstract

Cavitation in a tip vortex remains a challenging issue in a variety of engineering problems. In this study, we perform large eddy simulation of wetted and cavitating flows around a stationary elliptical hydrofoil with the cross section of NACA (National Advisory Committee for Aeronautics) 16-020. The Schnerr-Sauer cavitation model is adopted for phase transport. The numerical results are verified by comparing with the experimental measurements. Instantaneous vorticity and pressure in both wetted and cavitating flows are studied. It is found that the cavitation promotes the production of vorticity and increases the boundary layer thickness. To further analyze the influence of cavitation on the tip vortices, each term in the transport equation of enstrophy is examined. In the cavitating flow, the dilatation and baroclinic torque terms are promoted to be equally dominant as the vortex stretching term, while in the wetted flow the stretching term is the only dominant one. The axial and azimuthal velocities in the cavity are smaller than those in wetted tip-vortical flow, while the pressure inside is nearly equal to the constant saturation pressure. A tip vortex model with four regions in cavitating flow is built and compared to the wetted flow model. A weakly meandering motion of the tip vortex is observed in the near field. To study the surface wave behaviors of the tip vortex, the space-time velocity correlation analysis is carried out. The surface wave moves at a speed smaller than the incoming flow. A dominating helical mode is found and is consistent with the analytical and experimental results.