Abstract: For the side inlet/outlet of a pumped storage power station, because its bottom elevation is lower than that of the reservoir, it is connected to the reservoir via an open channel with a reverse slope, and the reverse slope ratio usually affects flow characteristics. In the previous designs of such inlets/outlets, no recommended values of the reverse slope ratio have been available. This paper presents a numerical simulation study on the influence of different reverse slope ratios in the range of 1:1 - 1:6 on the hydraulic characteristics of the inlet and outlet. The results show that the head loss coefficient of the inlet/outlet and the velocity distribution at the trashrack cross-section are affected by this slope ratio only when operating in inflow mode. In this case, typical inlet flow patterns are featured with a recirculation zone with a significant depth forming in the upper layer of the flow in the internal adjustment section of the inlet, and a smaller slope ratio leads to a smaller area ratio of this zone; when the slope ratio is less than 1:3, no backflow occurs in the reverse slope section of the open channel. In outflow mode of different slope ratios, such backflows appear in the reverse slope section of the middle and side passages of the outlet; the recirculation zone length ratio (relative to tunnel height) in the side passage is larger than that in the middle passage, and a smaller slope ratio leads to a larger length ratio. As the slope ratio of the outlet decreases from 1:1 to 1:6, flow in its platform section diffuses more evenly into the reservoir water body; when the ratio is 1:3 - 1:4, the inlet/outlet is best in hydraulics.

Key words: pumped storage power station, side inlet/outlet, reverse slope ratio, hydraulic characteristics, numerical simulation