Analysis of cavitating flow structure by experimental and numerical investigations

The unsteady structure of cavitating flows is investigated by coupled experimental and numerical means. Experiments focus on the structure and dynamics of sheet cavitation on the upper side of a two-dimensional foil section in the ENSTA cavitation tunnel. Various flow conditions are investigated by varying the pressure, the flow velocity, and the incidence of the foil section. High-frequency local measurements of volume fractions of the vapour phase are performed inside the liquid/vapour mixture by X-ray absorption method. The numerical approach is based on a macroscopic formulation of the balance equations for a two-phase flow. The assumptions required by this formulation are detailed and they are shown to be common to almost all the models used to simulate cavitating flows. In the present case we apply a single-fluid model associated with a barotropic state law that governs the mixture density evolution. Numerical simulations are performed at the experimental conditions and the results are compared to the experimental data. A reliable agreement is obtained for the internal structure of the cavity for incidence varying between 3 degrees and 6 degrees. Special attention is paid to the mechanisms of partial and transitional instabilities, and to the effects of the interaction between the two sides of the foil section.