Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments

Abstract

The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode.The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation.The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results.The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.