Preliminary design of adjustable Guide Vanes for PaTs in Pumped storage applications

Pumped-Storage Hydropower Plants (PSHPs) are a well-established technology for storing large amounts of energy and enhancing the power systems flexibility. In the framework of Micro and Mini Hydropower, Pumps as Turbines (PaTs) could represent a valid cost-effective solution also for PSHPs. Nonetheless, the lack of a control device could represent a problem, mainly with non-fixed operating conditions. Additionally, PaTs show generally a steep efficiency decrease at part load. Thus, since conventional PaTs do not present adjustable geometries, a preliminary sizing of an adjustable Inlet Guide Vane (IGV), referring to turbine mode, is proposed in this work. The aim of this work is to propose a methodology suitable to modify a baseline PaT introducing an adjustable IGV to perform a high efficient control in terms of flow rate and pressure drop. The machine selected for the proposed study is a centrifugal pump with a specific speed, nq, equal to 16. The adjustable IGV are inserted between the volute cutwater and the impeller by reducing impeller diameter. To obtain an initial solution for the stationary blades row profile, a review of Francis turbines guide vanes design methods is conducted. Finally, a numerical study on the influence of guide vanes number is performed.