Unsteady Sheet Cavitation on Three-dimensional Hydrofoil

An unstructured grid computational method for solving the Euler equations for inviscid compressible unsteady flow is employed to predict the structure and dynamics of three-dimensional unsteady sheet cavitation as it occurs on stationary hydrofoils, placed in a steady uniform inflow. For phase transition an equilibrium cavitation model is employed, which assumes local thermodynamic and mechanical equilibrium in the two-phase flow region, which depends on the equations of state of the vapor and (compressible) liquid only, see (Koop 2008). The method is similar to the method developed by Schnerr, Sezal & Schmidt (2008) for structured grids. The unsteady behavior of the flow, i.e. the formation of reentrant jets, their impingement on the cavity surface, the resulting shedding of the sheet cavity and the subsequent collapse of the bubble cloud, is inertia driven and it is shown that a numerical method based on the Euler equations is capable of capturing the phenomena associated with unsteady sheet cavitation. Due to the collapse of shed vapor structures strong pressure pulses are generated continually. To be able to predict the dynamics of the pressure waves, it is essential that the fluid is considered as a compressible medium by adopting appropriate equations of state for the liquid phase, the two-phase mixture and the vapor phase of the fluid. The three-dimensional unsteady cavitating flow about model configuration (3D Twist11 hydrofoil) is calculated for which experimental data is available (Foeth 2008). It is shown that the formation of re-entrant flow and of a cavitating horse-shoe-vortex is captured by the present numerical method. The calculated results agree reasonable well with experimental observations. Furthermore, the collapse of the shed vapor structures and the resulting high pressure pulses is demonstrated.