Transient flow calculation for sloping ceiling tailwater tunnels and their body-type design for hydropower stations

A study is made on the methods for calculation of the unsteady freesurface pressurized flow in tailwater tunnels with a sloping ceiling and their bodytype design, and an introduction is given to their operational characteristics. Based on the improved slot model, a transient flow calculation is performed to verify the scheme of canceling the tailwater surge tank at a largescale hydropower station, and a separation point treatment method for the unsteady freesurface pressurized flow is proposed. Aiming at tailwater tunnels with different top and base slopes and different bottom widths, a comparative analysis is made on the calculated results under some adverse conditions. The results indicate that, by reasonable selection of the bodytype parameters, the tailwater tunnel with a sloping ceiling can replace the tailwater surge tank, so it is feasible to cancel the surge tank, and that the gradient of the top slope has a great effect on the tailwater system, while the effects of the gradient of the base slope and bottom width are relatively small.