Numerical Investigation of the Pump, Energy-Dissipation and Turbine Regimes of a Radial Centrifugal Pump Converted into a PaT

Abstract

Centrifugal pumps operating as turbines (PaTs) are cost-effective for energy recovery, but the transitional energy-dissipation regime between pump and turbine modes remains underexplored. This paper presents a computational fluid dynamics (CFD) investigation of a radial centrifugal pump operating across three consecutive regimes: normal pumping, energy-dissipation, and turbine operation. A 3D numerical model is developed, validated against experimental measurements, and proven through a mesh-independence study to accurately capture global performance characteristics. Rather than the full four-quadrant map, this study deliberately focuses on the continuous path from near shut-off, through the dissipation zone, to stable turbine operation. Beyond reproducing characteristic curves and best-efficiency points (BEPs), the analysis emphasizes internal flow behaviour near regime transitions. The results reveal complex flow features—including recirculation, separation, and strongly unsteady structures—that govern these transitions. These findings provide critical physical insights into off-design operation mechanisms not captured by standard performance curves, ultimately contributing to the more reliable design and operation of PaT installations.