Performance and rangeability enhancement of a pump as turbine embedding variable Inlet Guide Vanes

Pumps as Turbines (PaTs), also referred to as Hydraulic Power Recovery Turbines (HPRTs) in several industrial applications, are emerging as a viable solution for smallscale hydropower applications. However, their efficiency at part-load conditions remains a significant drawback due to the lack of an inlet flow control mechanism. Therefore, this work, in collaboration with the industrial partner Nuovo Pignone srl, investigates the feasibility of enhancing the operational range of a HPRT by embedding Variable Inlet Guide Vane (VIGV). For this study, a low-specific-speed centrifugal pump is selected. This machine has been retrofitted by embedding the VIGV between the volute cutwater and the impeller while keeping the original pump body. To accommodate this modification, the impeller has been trimmed to make place to the VIGV and its kinematics in order to obtain a compact solution. A design methodology for the VIGV is presented, surveying the best practices in Francis turbine guide vane design. Computational Fluid Dynamics (CFD) analyses are conducted to evaluate the flow characteristics before and after the VIGV installation, providing insight into loss mechanisms and performance variations. The results highlight a 25% improvement in part-load efficiency. Additionally, the VIGV increased the rangeability of the machine by 0.25 of the flow rate at the best efficiency point (BEP). Furthermore, a cycle-based analysis of variable operating conditions demonstrates a 25% increase in harvested power. These findings confirm that embedding a Variable IGV substantially improves PaT performance, making them a more efficient and adaptable solution for energy recovery applications.