Modelling Cavitation Mechanisms Using Large Eddy Simulation

Doktorsavhandling, 2013

Cavitation often brings negative effects such as performance degradation, noise and vibration, and material damage, being one of the limiting factors when designing propulsion systems. On the other hand, cavitation must be endured for an efficiently propelled system. Therefore it is of great interest to learn about the cavitation mechanisms in order to avoid negative cavitation effects and improve the general performance of propulsors. Experiments can offer direct visualization of this complex process however analysis is quite limited. Together with accurate numerical predictions, a more complete picture of the cavitation process may appear, allowing detailed investigations to help improving both the understanding of the mechanisms and the design. In this thesis, numerical simulations of cavitating flow on hydrofoils and propellers are carried out using Large Eddy Simulation (LES) in combination with a single fluid mixture assumption based on a Volume-Of-Fluid (VOF) implementation and Transport Equation-based Methods for the mass transfer between the phases. The investigated mechanisms are mainly related to cavitation erosion, including large-scale hydrodynamic mechanisms that could initiate the focusing of the collapse energy, as well as the moderately small-scale processes associated with the final collapse and rebound phase. The overall simulation results are encouraging, having a satisfactory agreement with experiments, but maybe more importantly helping in better understanding the experimentally observed phenomena that are otherwise not possible to obtain from the experiment alone. The main conclusion of this thesis is that for studying the details of a cavitating flow field, LES is a useful and reliable tool from academic perspective to improve the knowledge regarding cavitation erosion; for industrial purposes it also has a great potential to guide the actual development of the design tools and principles.