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Abstract

The flow in the Pelton turbine bucket is three-dimensional, unsteady, turbulent, features a free surface, and is influenced by the rotation-induced forces. It is therefore difficult to investigate how the energy transfer takes place between the water flow and the buckets inner surface. The analysis of experimentally validated CFD results provides the opportunity to have a deep insight of the flow in the buckets. This paper presents the numerical investigations of the flow in a single bucket along a bucket period for an operating point close to the best efficiency of a 4-jet Pelton turbine model. The time history of the successive events occurring during the bucket period is first briefly presented. Then, the comparison of the pressure fields and the torque contribution for 5 different zones in the bucket is carried out. Significant discrepancies between the bucket pressure and torque distribution appear, highlighting that the regions, that are the most loaded in terms of mechanical strain, do not contribute the most to the bucket torque. This seems not to be related to the radial location of the bucket zones, but to the flow patterns, that are driven by the bucket design, and operating conditions. This study shows that an analysis of the bucket pressure and torque fields is paramount to quantitatively assess the effective energy transfer in the bucket.

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