A cavitation model for computations of unsteady cavitating flows

Abstract

A local vortical cavitation (LVC) model for the computation of unsteady cavitation is proposed. The model is derived from the Rayleigh–Plesset equations, and takes into account the relations between the cavitation bubble radius and local vortical effects. Calculations of unsteady cloud cavitating flows around a Clark-Y hydrofoil are performed to assess the predictive capability of the LVC model using well-documented experimental data. Compared with the conventional Zwart’s model, better agreement is observed between the predictions of the LVC model and experimental data, including measurements of time-averaged flow structures, instantaneous cavity shapes and the frequency of the cloud cavity shedding process. Based on the predictions of the LVC model, it is demonstrated that the evaporation process largely concentrates in the core region of the leading edge vorticity in accordance with the growth in the attached cavity, and the condensation process concentrates in the core region of the trailing edge vorticity, which corresponds to the spread of the rear component of the attached cavity. When the attached cavity breaks up and moves downstream, the condensation area fully transports to the wake region, which is in accordance with the dissipation of the detached cavity. Furthermore, using vorticity transport equations, we also find that the periodic formation, breakup, and shedding of the sheet/cloud cavities, along with the associated baroclinic torque, are important mechanisms for vorticity production and modification. When the attached cavity grows, the liquid–vapour interface that moves towards the trailing edge enhances the vorticity in the attached cavity closure region. As the re-entrant jet moves upstream, the wavy/bubbly cavity interface enhances the vorticity near the trailing edge. At the end of the cycle, the break-up of the stable attached cavity is the main reason for the vorticity enhancement near the suction surface. A local vortical cavitation (LVC) model for the computation of unsteady cavitation is proposed. The model is derived from the Rayleigh–Plesset equations, and takes into account the relations between the cavitation bubble radius and local vortical effects. Compared with the conventional Zwart’s model, better agreement is observed between the predictions of the LVC model and experimental data, including measurements of time-averaged flow structures, instantaneous cavity shapes, and the frequency of the cloud cavity shedding process.