Rans Computations of a Cavitating Tip Vortex

Abstract

The Swiss national research project Hydronet 2 gathers a consortium of industrial and academic partners supported by the Competence Center of Energy and Mobility (CCEM) and Swiss Electric Research (SER) in order to improve the hydropower plants. One of the research topic focuses on the cavitating tip vortex. Such a vortex takes place in axial turbines as Kaplan turbines used for producing hydroelectricity. This phenomenon drives a lot of drawbacks such as erosion, unsteady flow rate and a decrease of the turbine efficiency. To better understand the behaviour of the tip vortex, computations of a simple test case are performed. The test case consists in a NACA profile mounted in a channel with a gap between the NACA tip and the lateral wall. The computations are carried out with the OpenFOAM solver both in one-phase and two-phase flows. The turbulent motion is modelled with a RANS approach. For the two-phase flow computations, the phase change between liquid and vapour is achieved with the model proposed by Kunz. The results will be compared in cavitating and non-cavitating cases with the experimental data provided by the EPFL Laboratory for Hydraulic Machines. The comparisons deal with global picture of the flow, the trajectory of the tip vortex and the velocity field downstream the NACA profile.