Transition Mechanisms in Sheet to Cloud Cavitation.

We investigate sheet to cloud cavitation over a wedge using numerical simulations performed at Reynolds number, Re=200,000, and cavitation numbers ranging from σ=1.44 to σ=2.18. The multiphase fluid is described using a homogeneous mixture model, and the governing equations are the compressible Navier Stokes equations for the liquid/vapor mixture, along with a transport equation for the vapor mass fraction. The numerical method, a characteristic-based filtering approach for shock and interface capturing, is first validated by comparison with experiments, showing good agreement. A systematic parametric investigation for different cavitation numbers is then carried out. The two primary mechanisms known to destabilize the sheet cavity, viz. the re-entrant jet and condensation shock mechanisms, are captured in the simulations. The observations are then used to propose a novel description of the condensation shock mechanism, which can be initiated by a re-entrant jet that transforms into a shock front as it travels upstream through the vapor cavity. The results presented here are part of an ongoing investigation on identifying the physical conditions that lead to the transition between the re-entrant jet and condensation shock mechanisms, a knowledge of which is yet to be elucidated.