The weakly compressible and incompressible fluid flows in the penstock of a pumped storage power station are simulated under the load rejection condition by solving three-dimensional, unsteady and turbulent N-S equations along with an involved time-dependent flow rate subroutine, respectively. A couple of important time-dependent parameters, such as pressure, flow rate in several measurement sections in the penstock, water level in the surge tank, pressure at the penstock outlet as well as flow patterns in the penstock, have been obtained. The predicted transient pressure profiles are compared with the measurements. The pressure given by the weakly compressible fluid model is closer to the experimental data than those obtained by the incompressible fluid model and one-dimensional cha-racteristics method, showing a 0.16% better accuracy and 10.87 m pressure reduction at the penstock outlet. Compared with one-dimensional characteristics method, numerical simulation has more advantages in clarifying flow patterns in a penstock and tracking instantaneous water level in the surge tank. These results may be useful for understanding load rejection condition of hydro-turbine and provide some new ideas for simulating an unsteady flow in pumped storage power stations.
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