Abstract: The pumping stations along the Yangtze River have been used for the bidirectional tasks of water diversion and drainage such as irrigation, storm drainage, and water environment control. Influenced by the tidal level in the river, these bidirectional pumping stations often operate near zero head, while the actual flow rates exceed the design value by up to 30%. This leads to an increase in the hydraulic loss of flow passages, a disorder in flow patterns, and a potential of hydraulic vibrations, thereby affecting the operation safety of the pump systems. This study examines the flow behaviors and pressure fluctuations for a low-head pumping station through CFD simulations, and verifies the calculations using scale model tests. The results show that under the super-low head condition, large-scale backflows occur in the blind end of its inlet and outlet passages, and the one at the outlet has a great intensity and causes a significant increase in hydraulic loss. At all the measuring points in the inlet passage, the dominant and secondary frequencies of fluctuations are 6 and 1/8 times the pump rotating frequency respectively. in the outlet, the dominant frequencies are irregular, but the amplitudes at different locations are similar and low-frequency fluctuations are dominant.

Key words: pumping station, super-low head, two-way passage, pressure fluctuation, numerical simulation