Effect of the operating head for hydraulic performance and flow of a Pelton turbine

The unsteady multi-phase flow simulation in rotating buckets of a model Pelton turbine under various operating heads was performed with the SST-CC turbulence model. The hydraulic performance of the turbine and the flow pattern in the rotating bucket under different operating heads were discussed. The results showed that there was an optimal operating head for the Pelton turbine. The waste of the additional kinetic energy carried by the outflow under off-design heads accounted for the decline in the turbine efficiency. Moreover, the temporal and spatial distribution of the outflowing loss varied with operating head. In the case of high operating head, the outflowing loss last only a short period of time after the water sheet flow started to discharge, and the obvious region of loss was near the bucket root. In the case of low operating head, the outflowing loss occurred during the second half of jet-receiving for the bucket, with the position of high outflowing velocity distributed along the entire brim.