Propulsion of flapping foils undergoing in-plane clap-and-fling and deviation motions

Abstract: This study examines the performance of two flapping flat-plate foils interacting with each other while generating thrust at a Reynolds number of 800 through two-dimensional numerical simulations. These fluid dynamics simulations were conducted with a commercial computational fluid dynamics solver implementing a finite-volume method and an overset mesh capability. The foils performed a combined motion involving pitching, heaving, and deviation. Both foils exhibit similar movements, with one foil mirroring the other. The heaving and pitching motions occur at the same frequency but with a phase shift between them. The effects of varying the phase shift and the minimum spacing between the foils during motion were first explored. The study revealed that a maximum efficiency of 0.542 can be achieved by using two foils, representing an increase of 13.5% relative to the optimal single-foil case. Then, the impacts of the deviation motion were investigated. The deviation motion was introduced with a frequency twice as fast as the other motions, and a phase shift relative to the heaving motion. The other parameters such as the minimum spacing between the foils, the heaving and pitching amplitudes, and the frequency were those of the best configuration without deviation. The numerical simulations demonstrated that deviation can increase efficiency further to a value of 0.560, a relative increase of 3.95%.