Flow interactions in Pelton turbines and the hydraulic efficiency of the turbine system

Theoretical analysis has been performed to investigate the flow interaction between the jet and the rotating buckets as well as the relative flow in the buckets of Pelton turbines. The detailed calculation of cut-off processes of the jet by the rotating buckets provides the foundation both in evaluating existing layouts of Pelton turbines and in designing new ones. For achieving regular impact of the jet onto the buckets with minimum force fluctuations, the coincidence condition has been introduced, with which the optimum number of buckets for the Pelton wheel can also be determined. The effects of both centrifugal and Coriolis forces in the rotating bucket have been outlined in detail. In using the energy law to describe the relative flow of water in the rotating bucket, the so-called invariance equation has been derived and extended to apply to all parallel jet layers. This extension greatly simplifies the calculation of relative flow and hydraulic efficiency. Detailed calculation processes have been presented to quantitatively estimate the hydraulic efficiencies and their dependence on both the operating conditions and the bucket exit shapes.