A multiobjective optimization for improving the turbine output and efficiency of a counterrotating type pump-turbine unit operated at turbine mode was carried out in this work. The blade geometry of both the runners was optimized using a hybrid multiobjective evolutionary algorithm coupled with a surrogate model. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model were discretized by finite volume approximations and solved on hexahedral grids to analyze the flow in the pump-turbine unit. As major hydrodynamic performance parameters, the turbine output and efficiency were selected as objective functions with two design variables related to the hub profiles of both the runner blades. These objectives were numerically assessed at twelve design points selected by Latin hypercube sampling in the design space. Response surface approximation models for the objectives were constructed based on the objective function values at the design points. A fast nondominated sorting genetic algorithm for the local search coupled with the response surface approximation models was applied to determine the global Pareto-optimal solutions. The trade-off between the two objectives was determined and described with respect to the Pareto-optimal solutions. The results of this work showed that the turbine outputs and efficiencies of optimized pump-turbine units were simultaneously improved in comparison to the reference unit.
It is difficult, for renewable energy resources, to provide constant power with excellent quality for the grid system. This serial research proposes a power stabilization system with a pumped storage to guarantee the power quality and capacity, while the energy resources are at unstable and/or fluctuating conditions. The power stabilization system with the counter-rotating type pump-turbine unit was prepared and operated at the pumping and the turbine modes. The experiments have verified that this type pump-turbine unit is reasonably effective to stabilize momentarily/instantaneously the fluctuating power from the renewable energy resources.
Abstract. This serial research proposes the hybrid power stabilization system with the counter-rotating type pump-turbine unit, to stabilize momentarily fluctuating power from renewable energy resources. In this paper, the experiments are verified that this type pump-turbine unit is reasonably effective to stabilize momentarily/instantaneously the unstably fluctuating power from renewable energy resources. Furthermore, an optimization for improving the hydrodynamic performance at turbine mode of this pump-turbine unit is carried out by using numerical analysis based on three-dimensional Reynolds-averaged Navier-Stokes equations. As a result, the optimization yielded a maximum increase in efficiency of 2.68% at the best efficiency point compared to a reference design. Detailed internal flow fields between the reference and optimum designs are analyzed and discussed in this work.
Pumped storage system contributes to adjust the electric power unbalance between day and night, in general. The pumping operation, however, may be unstable in the rising portion of the head characteristics, and/or bring the cavitation at the low suction head. To simultaneously overcome both weak points, the authors have proposed a superior pumping unit that is composed of counter-rotating type impellers and a peculiar motor with double rotational armatures. This paper discusses the operation at the turbine mode of the above unit. It is concluded with the numerical simulations that this type unit can be also operated acceptably at the turbine mode, because the unit works so as to coincide the angular momentum change through the front runners/impellers with that thorough the rear runners/impellers, namely to take the axial flow at not only the inlet but also the outlet without the guide vanes.
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