Hydrodynamic response of tandem bionic dual-hydrofoil pump to relative foil spacing and frequency variations

A compound harmonic motion-based tandem bionic dual-hydrofoil pump is developed to optimize hydrodynamic conditions and hydrologic exchange frequency in plain river networks suffering from flow stagnation and degraded self-cleaning functions. This study employs the Finite Volume Method (FVM) and overset mesh technology to investigate the hydrodynamic performance of the tandem dual-hydrofoil pump. A total of 11 different relative foil spacings and 4 flapping frequencies are selected as experimental variables. Through numerical simulations, the effects of relative foil spacing and flapping frequency on the hydrodynamic performance of the tandem dual-hydrofoil pump are systematically analyzed, with a comparative study against a single flapping foil. The results demonstrate that the optimal relative foil spacings for both propulsive and pumping efficiencies were identified at R = 0.25 and R = 3.0, whereas the least favorable performance occurred at R = 1.0 and R = 3.5. Notably, while the tandem configuration's peak pumping efficiency surpassed single-foil performance by 34.1 %, it never reached twice the single-foil baseline. The flapping frequency primarily affects the head and flow rate of the tandem bionic dual-hydrofoil, but has little influence on the pumping and propulsive efficiencies. • The vortex street offset is the key factor affecting the pumping and propulsion efficiencies of the dual-hydrofoil pump. • Compared to a single hydrofoil, the dual-hydrofoil pump has higher efficiency at R=0.25, 3.0 but lower at R=1.0, 3.5. • Relative spacing alters the tandem pump's flow field, thus affecting its hydrodynamic performance. • Efficiencies peak at R=0.25 and R=3.0, but reach minima at R=1.0 and R=3.5 for small and large spacings, respectively.