a b s t r a c tA novel modular pumped-storage scheme is investigated that uses elevated water storage towers and cement pools as the upper and lower reservoirs. The scheme serves a second purpose as part of the wastewater treatment process, providing multiple benefits besides energy storage. A small pumped-storage scheme has been shown to be a competitive energy storage solution for micro renewable energy grids; however, pumped-storage schemes have not been implemented on scales smaller than megawatts. Off-the-shelf runner designs are not available for modular pumped-storage schemes, so a custom runner design is sought. A preliminary hydraulic design for a pump-turbine runner is examined and optimized for increased pumping hydraulic efficiency using a response surface optimization methodology. The hydraulic pumping efficiency was found to have improved by 1.06% at the best efficiency point, while turbine hydraulic efficiency decreased by 0.70% at the turbine best efficiency point. The round-trip efficiency for the system was estimated to be about 78%, which is comparable to larger pumped-storage schemes currently in operation.
Predicting hydrokinetic turbine power generation is difficult due to complex geometry, highly turbulent conditions, and difficulty capturing the transient interface existing between air and water.A threedimensional finite volume solver was used to capture the effects resulting from free surface interaction with the aid of a Volume of Fluid(VOF) multiphase solver.Depths from free surface level to blade tip with corresponding Froude numbers of 0.71, 0.92, 1.04, and 1.31 were modelled specifically to capture the transition from subcritical to supercritical flow conditions.A sharp decrease in performance was observed at the critical Froude number (Fr=1.0).Results at subcritical conditions showed acceptable agreement with previously published single phase results where the turbine is assumed to be operating in aninfinite medium.At subcritical conditions, the propeller-based turbine studied was compared to numerical and experimental results obtained for a traditional marine current turbine (MCT).As the flow became critical, a 32.2% decrease in the power coefficient was predicted and significant wake-free surface interaction was observed.
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