Heaving foil propulsion performance under combined base and perturbation signal inputs

The thrust variation, efficiency, and wake evolution of a flapping foil were investigated for a variety of base and perturbation frequencies. The study was inspired by the complex environment in which fish swim. In this numerical study, the waveform of the perturbation signal was adjusted by the waveform parameter k. The results demonstrate that the addition of perturbations increases thrust in the majority of cases, with square wave perturbations having the most substantial effect. However, the addition of a perturbation signal reduces the propulsion efficiency; a square wave perturbation significantly reduces the propulsion efficiency, while a sinusoidal or approximate sawtooth wave perturbation slightly decrease the propulsion efficiency. The change in the wake structure is closely related to the perturbation signal waveform, base frequency magnitude, and perturbation frequency magnitude, according to the wake structure analysis. The present work provides useful findings for optimizing underwater vehicle motion parameters.