Narrow Results

Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.

A new transport equation model is proposed for simulating cavitating flows in miniature machines. In the developed model, the surface tension, viscous force, and thermal effect of cavitation are considered to reflect their influence on the cavitation bubble growth. The cavitating flow in a miniature pump is calculated by applying the proposed cavitation model. The comparison between numerical results and experimental data indicates that the new cavitation model is applicable for simulating the cavitating flow in miniature machines.

Modeling of unsteady cavitating flow is a critical issue in a lot of practical cases. The objective of this paper is to assess the practical applicability of three widely used mass transport cavitation models under RANS framework, including the Kubota model, Kunz model, and Singhal model, for predicting partial sheet cavitating flow around an axisymmetric body with hemispherical head and unsteady cloud cavitating flow around a Clark-Y hydrofoil. The results show that for the axisymmetric cylindrical body, all three cavitation models could generally predict the pressure distributions. The significant differences are found around the closure region of the attached cavity due to the magnitude and distribution of mass transfer rate. For the unsteady cavitating flow along the hydrofoil, the significant differences with different cavitation model are observed in time-averaged and time-dependent concerning the cavity shapes, multiphase structures and the cloud shedding dynamics. The Singhal model coupling the effect between the vorticity distribution and the cavity dynamics agrees best with the experimental measurements.