Experimental and Theoretical Investigations of the Flow Field at the Inlet of a Francis Runner

This paper presents and discusses CFD simulations performed in order to investigate the dynamic load inflicted to the runner blade by the outflow from stay vane and wicket gate. The CFD simulations are compared to the results from laboratory experiments in a blade cascade. LDV-measurements of velocity distribution in a cascade for various guide vane profiles were carried out. Later, pressure pulsations in a model turbine where the different guide vane profiles were implemented, was investigated. This is not treated in this paper. For the experiments, a special test rig witch is a 1:2.5 scaled homologous model of the last quarter of a high head Francis turbine, including 5 stay vanes and 5 guide vanes, was used. The velocity profile between the guide vanes were measured by LDV. An overall goal of this project is to improve the accuracy of the theoretical predictions of the dynamic pressure fluctuations at the boundary between the distributor and the runner. A better prediction of the oscillating forces on the blade is essential in order to secure structural safety.