The jet discharged from the nozzle of a Pelton turbine is a key item of such hydropower systems and its precise shape and position are highly relevant to the optimum design of the turbine buckets to match the incoming flow. Experimental investigations, primarily with laser Doppler anemometry, have been used to identify the important fluid dynamic structures of the jet and its free surface. It is shown that weak secondary flows generated by the bends or bifurcations in the distributor of the Pelton turbine system are still present in the jet leaving the injectors. These cause small flow disturbances which affect the shape, orientation, and the topology of the jets and lead to a shift of the jet core from the axis of the nozzle.

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.

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