Yang Lin

To improve the pumping performance of biomimetic flapping-wing devices in small river channels, this study introduces high-frequency disturbances in the heave direction based on traditional pitch–heave motion. A systematic investigation of the forces and hydrodynamic performance is conducted using numerical simulations, with vortex contour analysis to explore the evolution mechanism of the wake vortex structure. The results show that high-frequency disturbances cause the instantaneous thrust to exhibit an amplitude modulation feature, with thrust oscillating approximately f_p/f_b times within one base frequency cycle. As the disturbance frequency increases, the average thrust also increases. There is a significant frequency-dependent difference in performance: at low disturbance frequencies (f_p/f_b ≤ 16), changes in thrust, pressure difference, and flow rate are limited, with little improvement in pumping efficiency; at intermediate frequencies (16 < f_p/f_b ≤ 32), wake coherence and jet momentum flux are significantly enhanced, and both thrust and pumping efficiency reach their maximum (up to 47%); at high disturbance frequencies (f_p/f_b > 32), although the vortex structure is further strengthened, input power increases sharply, leading to a decrease in efficiency. Overall, moderate disturbance frequencies can effectively enhance the thrust and pumping performance of the flapping wing, while excessively high frequencies do not offer an advantage due to the high energy cost.

The bionic pumping system can effectively improve the hydrodynamic conditions in plain river networks, thereby mitigating the frequent algal blooms in these regions. This study employs numerical simulations to investigate how heave amplitude and chord length affect the hydrodynamic performance of both multi-hydrofoil and single-hydrofoil systems. The operating frequencies for the two configurations are selected by combining these results with the flow velocity threshold required to suppress algal blooms. The results show that the pumping efficiency of the multi-hydrofoil system increases with chord length and heave amplitude, and the optimal parameter combination is c = 0.18W and h_max = 0.7c. For the single-hydrofoil system, efficiency first rises and then falls, peaking at c = 0.16 W and h_max = 0.6c. Under the algal bloom suppression threshold of 0.15 m/s, the multi-hydrofoil system meets the criterion across the entire cross-section at 0.10 Hz, making it suitable for raising flow velocity throughout the water body and for comprehensive bloom suppression. By contrast, the single-hydrofoil system produces an uneven wake with lower velocities in the upper region, so even at higher operating frequencies, it cannot cover the entire cross-section; it is therefore more appropriate for localized velocity enhancement and localized suppression of algal accumulation.

This study aims to optimize bionic hydrofoil propulsion performance and establish design guidelines for efficient transmission mechanisms by comparing three mechanisms (crank-slider, cylindrical cam, and synchronous belt drive). Through 3D modeling, virtual assembly, and ADAMS simulations, dynamic responses of slider displacement and driving force/torque were obtained, revealing that the crank-slider consumes the least energy, followed by the cylindrical cam, with the synchronous belt being the most energy-intensive. Further CFD analysis demonstrated that while the crank-slider generates drag intermittently, the cylindrical cam and synchronous belt sustain continuous thrust. All mechanisms achieve effective water propulsion below their critical frequencies (0.25 Hz, 0.75 Hz, and 1.4 Hz, respectively). Propulsion efficiency peaks at 26.0% (crank-slider) and 24.7% (cylindrical cam) at 0.25 Hz but declines at higher frequencies, whereas the synchronous belt reaches 24.3% efficiency at 1 Hz with superior frequency adaptability. The synchronous belt emerges as the optimal solution for efficient flapping propulsion due to its motion continuity and frequency adaptability. This work elucidates the critical impact of transmission mechanisms on hydrofoil hydrodynamics, providing foundational insights for mechanism design and performance optimization.

To improve hydrodynamic conditions and self-purification in plain river networks, this study optimized an existing hydrofoil-based pumping device and redesigned its flow channel. Using the finite volume method (FVM) and overset grid technique, a comparative numerical analysis was conducted on the pumping performance of hydrofoils operating under simple harmonic and quasi-harmonic flapping motions. Based on the tip vortex phenomenon observed at the channel outlet, the flow channel structure was further designed to inform the structural optimization of bionic pumping devices. Results show both modes generate reversed Kármán vortex streets, but the quasi-harmonic mode induces a displacement in vorticity distribution, whereas that of the simple harmonic motion extends farther downstream. Pumping efficiency under simple harmonic motion consistently outperforms that of quasi-harmonic motion, exceeding its peak by 20.2%. The pumping and propulsion efficiencies show a generally positive correlation with the outlet angle of the channel, both reaching their peak when the outlet angle α is −10°. Compared to an outlet angle of 0°, an outlet angle of −10° results in an 8.5% increase in pumping efficiency and a 10.2% increase in propulsion efficiency.