In this study, a counter-rotating-type pump-turbine unit was optimized to improve the pump and turbine mode efficiencies\nsimultaneously.Numerical analysis was carried out by solving three-dimensionalReynolds-averagedNavierââ?¬â??Stokes equations using\nthe shear stress turbulence model. The hub and tip blade angles of the rear impeller (in the pumpmode) were selected as the design\nvariables by conducting a sensitivity test. An optimization process based on steady flow analysis was conducted using a radial basis\nneural network surrogate model with Latin hypercube sampling. The pump and turbine mode efficiencies of the unit were selected\nas the objective functions and they combined into a single specific objective function with the weighting factors. Consequently, the\npump and turbine mode efficiencies of the optimum design increased simultaneously at overall range of flow rate, except for low\nflow rate of turbine mode, compared to the reference design.
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