Search

Cavitating flows always include micro-bubbles and macro-cavities over a wide range of length scale, and understanding the vorticity force evolution induced by cavitation is also a challenging issue. In the present work, a hybrid multiscale cavitation model incorporated with the large eddy simulation approach is applied for comprehensively revealing the unsteady cavitating flow features. The macroscale cavities are captured by the volume of fluid (VOF) method while the microscale bubbles are modeled using a discrete bubble model (DBM) in the Lagrangian way. Simulations of the cavitating flow on a twist hydrofoil are performed and validated against the experimental result. Good agreement in terms of cavity morphology and shedding frequency is obtained. Applying the multiscale cavitation model, the microscale cavitation bubbles that are unable to be predicted by the VOF method are well represented especially in the region near the trailing edge. To investigate the vorticity force evolution, the force element method is adopted to quantitatively analyze the change of force elements along with the evolution of the cavity. The overall effect of cavitation on the lift and drag forces is also investigated. Finally, the superiority of the multiscale VOF-DBM model is attested compared with the original VOF method. [ABSTRACT FROM AUTHOR]

For understanding tip-leakage cavitating flow features, the present work aims to implement a multiscale model to comprehensively reproduce the complicated phase structure. The volume of fluid (VOF) interface capturing method is applied to simulate macroscale cavities, while a discrete bubble model using the Lagrangian formulation is newly developed to take the microscale bubbles into account. The Schnerr–Sauer cavitation model is incorporated into the VOF model to calculate the mass transfer rate between phases from the macroscale point of view. For microscale bubbles, the simplified Rayleigh–Plesset equation is adopted to simulate the bubble growing and collapsing stages. An algorithm for coupling the approaches simulating macroscale cavities and microscale bubbles is also implemented to achieve multiscale simulation. Unsteady flow features are simulated using the large eddy simulation approach. The results show that an anti-diffusive compression scheme for the spatial discretization of volume fraction equation is relatively accurate for simulating the tip-leakage cavitating flow. Applying the multiscale model, the tip-leakage cavitating flow features with multiple time and space scales including the formation of glass cavity tube and the transport of bubble clouds can be revealed. Suitable model parameters including the coefficient of saturated pressure, and the bubble evaporation and condensation coefficients are studied. [ABSTRACT FROM AUTHOR]