Comparative Analysis of the Hydrodynamic Performance of Dual Flapping Foils with In-Phase and Out-of-Phase Oscillations

In the context of the plain river network, conventional water pumps suffer several drawbacks, including inadequate efficiency, poor security, and costly installation costs. In order to improve the hydrodynamic insufficiency problem and enhance the hydrodynamic performance and applicability of flapping hydrofoils, this paper proposes a bionic pumping device based on dual flapping foils. Based on the finite volume method and overlapping grid technology, the numerical simulation and experimental verification of the hydraulic performance of two typical motion modes of in-phase and out-of-phase oscillations are conducted, thereby providing a theoretical foundation for improving and optimizing the design of flapping hydrofoils. The results show that the out-of-phase oscillation has better hydraulic performance compared to the in-phase oscillation. The formation of the tail vortex structure plays a crucial role in determining the hydraulic efficiency of dual flapping foils, with in-phase oscillation forming a pair of vortex streets and out-of-phase oscillation forming two pairs of vortex streets. The pumping efficiency of the out-of-phase oscillation is significantly higher than that of the in-phase oscillation, reaching up to 38.4% at a fixed frequency of f = 1 Hz, which is an increase of 90.5% compared to the in-phase oscillation. The characteristic curve of the in-phase oscillation shows an “S” type unstable oscillation phenomenon, namely the hump phenomenon, while the out-of-phase oscillation does not show such a phenomenon, which can effectively expand its application range. In addition, the applicable head of the out-of-phase oscillation hydrofoil is lower, which can better meet the requirements of ultra-low head conditions.