A static and dynamic model for hydraulic transient calculation of three-throttled-orifice surge tank was established based on the basic equations of surge tank, by using structure matrix method (matrix analysis of structure?). Control conditions in an engineering practice were calculated by a simplified model and a three-throttled-orifice model respectively. The results indicate that the maximum pressure at the volute end, the maximum rising rate of unit speed and the water level extremum of the surge tank are basically identical by using these two models, but the minimum pressure at draft tube inlet is significantly different. The three-throttled-orifice model was found capable of calculate the flow between throttled orifices at constant state and the pressure behavior at draft tube inlet during the transition accurately. The selection of the resistance factor is discussed in the end, and it is proved that the resistance factor is allowed to have a certain tolerance in the transition calculation, which will not obviously affect the maximum pressure at draft tube inlet and water level extremum of the surge tank. This research can provide reliable reference for the transient calculation of three-throttled-orifice surge tank in similar engineering practice.

The downstream of a pumped storage power station is equipped with an impedance surge chamber, and the tailrace tunnel is connected with the connecting pipe through bifurcated pipes and bends. The layout type is special, and the water flow conditions are complex. Considering the complexity of the layout of the impedance surge chamber with long connecting pipe and the actual situation of engineering construction, this paper studies the flow pattern and flow coefficient at the bottom of the surge chamber under the typical layout. The variation laws of flow velocity distribution, pressure distribution and inlet and outlet flow coefficient at the bottom of the surge chamber with different layout schemes are obtained.

The Downstream Surge Chamber of a pumped storage power station adopts impedance with an upper chamber layout. The tailrace tunnel is connected with the connecting pipe through a right-angle bifurcated pipe and bend. The layout type is special and the water flow conditions are complex. To study its hydraulic characteristics, a three-dimensional flow field mathematical model of the connecting pipe at the bottom of the surge chamber is established, and the variation law of hydraulic characteristics under different diversion ratios and confluence ratios is studied. The results show that for the resistance loss of the surge chamber with the complex bottom flow, the three-dimensional numerical simulation can achieve a better simulation effect, and the calculation results are in good agreement with the theoretical analysis results. Because the elbow is at the bottom of the surge chamber, the sudden expansion and contraction between the connecting pipe and the big well will cause additional hydraulic losses, its head loss coefficient is greater than that of the conventional impedance surge chamber, and the flow coefficient is smaller than that of the separate impedance hole.