Interfacial dynamics-based modelling of turbulent cavitating flows, part-2: Time-dependent computations

The interfacial dynamics-based cavitation model, developed in Part-1, is further employed for unsteady flow computations. The pressure-based operator-splitting algorithm (PISO) is extended to handle the time-dependent cavitating flows with particular focus on the coupling of the cavitation and turbulence models, and the large density ratio associated with cavitation. Furthermore, the compressibility effect is important for unsteady cavitating flows because in a water-vapour mixture, depending on the composition, the speed of sound inside the cavity can vary by an order of magnitude. The implications of the issue of the speed of the sound are assessed with alternative modelling approaches. Depending on the geometric confinement of the nozzle, compressibility model and cavitation numbers, either auto-oscillation or quasi-steady behaviour is observed. The adverse pressure gradient in the closure region is stronger at the maximum cavity size. One can also observe that the mass transfer process contributes to the cavitation dynamics. Compared to the steady flow computations, the velocity and vapour volume fraction distributions within the cavity are noticeably improved with time-dependent computations.