Numerical and experimental studies on unsteady shedding mechanisms of cloud cavitation

The unsteady characterics of cloud cavitating flow around a hydrofoil are investigated by the experimental and numerical methods. Experiments on a hydrofoils are carried out in a rectangular test section of a cavitation tunnel. A high-speed video camera is used to visualize the unsteady flow structures. The calculations are conducted on the two-dimensional hydrofoil section, based on a single-fluid model of the cavitation: the liquid/vapor mixture is considered as a homogeneous fluid whose composition is regulated by mass tranfer equation. The RNG κ-ε turbulence model with modified eddy viscosity coefficient is used in the computation, and the coefficient is related to the vapor and liquid densities in cavitated regions for simulating the cavitating flow. The experimental and numerical results show the unsteady features of the peridical cloud cavity departure; the increasing of a local pressure is a main factor to induce ruture of a cloud cavity; an interaction between the re-entrant jet and the cavity interface in the closure region can lead to the increasing of the local pressure; the adverse pressure gradient is mainly responsible for the generation of the re-entrant jet.