| Cavitation is a phenomenon that frequently occurs in fluid-handling machinery, ranging from all types of pumps, turbines, and propellers to various piping systems and hydraulic structures. Cavitation research has been pursued for over a century and an enormous quantity of literature on cavitation has been generated. Cavitation modeling is challenging and is still in the development stage due to its inherent complexity of the physics involved. There are basically three objectives in this thesis work. First, an existing virtual single-phase natural cavitation model is used to extensively explore the unsteadiness of sheet/cloud cavitation on two hydrofoils (NACA 0015 and CAV2003). Five discrete vortex shedding mechanisms are identified in this research. Second, this existing virtual single-phase natural cavitation model is further modified to take into account the effect of incondensable gas that comes out of solution due to the cavitation evaporation process. This was motivated by the observation that the computed mean velocity distribution in the wake of a cavitating hydrofoil, without the effect of incondensable gas, agrees well with experimental data close to the trailing edge but deviates systematically further downstream. This revision shows a significant improvement on the computed mean velocity distribution in the wake compared to that without the incondensable gas effect and the results are in agreement with those from experiments. These are two new findings that are absent in literature. Third, a two-phase, fully compressible flow model based on Large Eddy Simulation (LES) for ventilated cavitating flows is developed and is successfully implemented in the simulation of an axisymmetric underwater body. |
