Numerical prediction of efficiency and cavitation for a Pelton turbine

The first part of the paper illustrates the set-up and the methodologies adopted for the numerical analysis of the flow in a 6-jet Pelton turbine with vertical axis. At first, steady state simulations of flow in a distributor for three positions of needle stroke were performed. The results were used for the calculation of flow energy losses, analysis of jet quality and setting inlet boundary conditions for runner analysis. Runner analysis was done only for the maximal opening. The purpose of runner analysis for the model size was efficiency prediction. Numerical results were validated with the results from the test rig. Simulations for the prototype were done in order to check whether water sheets evacuating from the buckets impact the previous bucket and whether there is any interaction between the evacuating water sheets and the incoming jets. Analysis was done also for one nozzle operation. In the second part of the paper cavitation prediction for the prototype of a 2-jet Pelton turbine is presented. The problem, because of computational cost, was reduced to five runner buckets and one jet. A multiphase flow consists of water, air and water vapour. For cavitation pitting the vapour has to stick to the buckets and mass transfer from vapour to water has to happen in a very short time without the presence of air. With detailed analysis of numerical results it was concluded that in this case no cavitation pitting is expected.