Abstract: To solve the problem of insufficient hydrodynamic force in plain river networks, a bionic flapping hydrofoil in compound harmonic motions is used to push water under ultra-low head operating conditions. Based on the finite volume method (FVM) and the overlapping moving grid technology, the optimal position of the hydrofoil pivot is determined by using numerical simulations and experimental tests. The result shows that an inverse Karman vortex street appears as the wake of the flapping hydrofoil, and the pivot position affects the deflection degree of the street, the strength of the leading edge vortex, and the time change in its instantaneous state. As the pivot moves towards the trailing edge, the water pushing efficiency rises first and then declines with an optimal value 2% - 5% higher at L = 0.2c than that of the pivot near the leading edge. The hydraulic characteristic curve of a flapping hydrofoil features similar to that of a traditional pump, and its maximum head is lower than 1 m. The maximum head gradually lowers as its pivot moves towards the trailing edge to meet the requirement of ultra-low head conditions.

Key words: flapping hydrofoil, numerical analysis, overlapping grid, experimental verification, water pushing performance, ultra-low head