Research on Internal Flow Characteristics in the Buckets of Pelton Turbines under Kilometer-Head Range

Against the backdrop of global energy transition and carbon neutrality strategies, the elevation of head parameters exerts multidimensional impacts on the performance and operational stability of Pelton turbines. This heightening tendency is prone to induce flow instability and issues like back-side bucket impact. Therefore, this study addresses the critical scientific problem of transient flow instability inside Pelton turbine buckets under extreme hydraulic conditions at kilometer-scale heads. A three-dimensional unsteady Computational Fluid Dynamics (CFD) model encompassing the complete runner flow domain was developed. Coupled with a multiphase flow calculation approach, this model was employed to analyze the flow evolution characteristics in Pelton turbines operating within the kilometer-head range. The results reveal that regions with a larger water volume on the bucket working surface exhibited relatively higher internal pressure. Conversely, despite a smaller water volume, localized areas impacted by high-velocity jet filaments also experienced significant pressure. A small negative pressure zone was consistently observed near the back-side of the bucket cutting edge. This phenomenon is attributed to local flow acceleration and separation. Consequently, the probability of cavitation occurrence increases, adversely affecting the hydraulic performance of Pelton turbines operating under kilometer heads.