The interaction between bucket number and performance of a Pelton turbine.

The Pelton turbine is a type of hydraulic turbine suitable for medium, high and ultra-high head hydropower exploitation. As energy conversion units, the Pelton turbine has numerous design parameters affecting its energy conversion efficiency. In this paper, a three-dimensional unsteady simulation was conducted to analyze the influence of bucket number on the hydraulic performance and internal flow behavior of a model Pelton turbine. Five different bucket numbers in a total runner were selected for numerical examination, including the optimal number of 21 determined by the empirical formula. As the bucket number increased with the same operating conditions, the predicted hydraulic efficiency of the Pelton turbine rose to the maximum under optimal bucket number and then decline. Compared with the optimal bucket number of 21, the hydraulic efficiency of the Pelton turbine with 15, 17 buckets decreased by 2.8 % and 1 % respectively. By analyzing the variation of torque coefficient and water sheet flow under different bucket numbers, the interacting mechanism between bucket number and performance of the Pelton turbine was discussed. Numerical result indicated that the phase difference of the single bucket torque coefficient affected by the flow pattern exerted an influence on mean of the runner torque coefficient and hydraulic efficiency. This paper provides an in-depth understanding of the bucket number to the flow mechanism in the bucket for exploring the energy conversion efficiency of the Pelton turbine. • Disclosed the interacting mechanism of bucket number on Pelton turbine performance. • Studied the water sheet flow behavior in a Pelton turbine with 5 bucket numbers. • Disclosed the effect of each bucket on runner torque with 5 bucket numbers. • Bucket cutout leakage flow caused the efficiency drop at low bucket numbers. [ABSTRACT FROM AUTHOR]