Unsteady dynamics of cloud cavitating flows around a hydrofoil

Abstract

The unsteady dynamics of cloud cavitating flow around a hydrofoil are investigated by joint experimental and numerical methods. Experiments 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 visualized data are analyzed by using a home made soft ware. The drag and lift under the cavitation condition are measured. The spectral analysis for the measured date is conducted. The computations 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 transfer equation. The RNG k- ? turbulence model with modified eddy viscosity coefficient is used for the computations, and the modified coefficient is related to the vapor and liquid densities in cavitated regions for simulating the cavitating flow. A good agreement is obtained between experimental data and numerical simulations. The cloud cavitating area is divided in two parts: attached vapor sheet in the foreside of the cavity, and unsteady two-phase mixture in the rear region in the process of cavity breaking off. The local pressure increasing induced by the re-entrant jet is the main reason to lead the cloud cavity. The adverse pressure gradient in the rear area of the cavity is mainly responsible for the generation of the re-entrant jet.