Understanding the shedding mechanism of partial cavitation is of importance for suppression or utilization of cavitation. To explore the condensation front mechanism of partial cavitation, flows in a three-dimensional axisymmetric Venturi are investigated by combining incompressible numerical simulation and a high-speed photography experiment at a cavitation number of 0.37 and a Reynolds number of $8.94\times {10}^4$. Based on the volume of fluid (VOF) multiphase flow model, the large eddy simulation (LES) method, and Sauer-Schnerr cavitation model are used to predict the generation and propagation process of the condensation front in the cavitating flow. The instantaneous flow topology and flow field, temporal evolution of cavity shedding, condensation front characteristics, and interaction between cavitation and vortex are expatiated. It is clearly shown that a condensation front is induced by the collapse of the cavitation cloud at the Venturi downstream and propagates inside the sheet cavity until triggering the “pinch off” of the cavity. Different from the cavitating flow on wedges or hydrofoils, a portion of vapor at the sheet cavity aft shows a negative axial velocity during the shedding process before the sheet cavity is influenced by the condensation front. This may be because of the strong squeezing effect resulting from the high-pressure downstream in the confined space of the Venturi. The condensation front satisfies the one-dimensional Rankine-Hugoniot jump condition most of the time (except for the initial propagation process) and exhibits supersonic characteristics. The predicted condensation front characteristics, such as propagation velocity and pressure rise, are identical to those found in previous studies. The supersonic regions exist on the condensation front and sheet cavity surface and in the vortices. The good agreement of the incompressible simulation results with the experimental results and the minor difference between the results of incompressible and compressible solvers prove that the condensation front is fundamentally different from traditional shock waves in aerodynamics. The density change resulting from evaporation and condensation of cavitation plays an important role in the formation and propagation of the condensation front, instead of compressibility. The findings of this work may provide a new understanding of the shedding mechanism of partial cavitation.

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• Cavitation
• Large eddy simulations
• Volume of fluid method