Approaching Large Eddy Simulation of Cavitating Flows for Marine Applications

Doktorsavhandling, 2006

Cavitation is a major concern in naval craft design as well as in the shipping industry. Although the nature of cavitation is not fully understood, propeller designs are presently improved by experimental analysis of the phenomena. Enhanced methods for the simulation of cavitating flow will become useful in design as well as in the efforts to characterise and understand cavitation. The thesis concerns simulation of cavitating flow using an incompressible solver employing a single continuum volume fraction approach for free surface capturing. Given the transient nature of cavitation and the flow problems targeted by the model, turbulence modelling is approached using Large Eddy Simulation, LES. The thesis concludes that the underlying method for modelling unsteady flow and in particular turbulence is of utmost importance to successful cavitation modelling, and due to resolution requirements demanded by the cavitation physics itself, LES is presented as a natural choice. A substantial part of the thesis is therefore dedicated to the evaluation of available LES methods and their application to marine flow problems. Since the work is primarily focused on marine applications, and the author believe that the implementability of the result into existing tools for e.g. ship flow computation is important, the choice of the incompressible Navier-Stokes equations becomes natural. The thesis finally concludes that the cavitation model is suitable for analysis of moderate to large scale cavitation on marine propulsors. It is observed, however, that an analysis using the presented method requires a computer effort not often available in industry