Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion

A numerical solution procedure using the mesh-superposition approach, known as the Chimera method, together with the OpenFOAM toolbox environment is used to compute the forces generated by large amplitude heaving and pitching foil. The possibility of fitting thrust prediction laws, based on classical potential flow theories, with the numerically computed forces is explored, for a Reynolds number of 5 104. It is shown, first for a pure heaving motion and subsequently by adding a harmonic pitching motion, that theoretical scaling may be fitted to numerical time-averaged thrust data, even in the case of large amplitude motions. The thrust-prediction law is shown to still apply to pitching-rotating motions, such as those of blades in cycloidal propulsion devices, the mean pressure correction due to the additional surging motion being small. The synchronized rotation-pitching of three foils typical of a cross-flow propeller configuration is addressed as well. The numerical global thrust results are shown to be in general agreement with the theoretical prediction, but also with blade-embedded load cell measurements for an experimental device developed by the French Naval Academy Research Institute.

Automated summary

The Chimera method, in combination with the OpenFOAM toolbox, is used to numerically compute the forces generated by large amplitude heaving and pitching foil. The study explores the possibility of fitting thrust prediction laws, based on classical potential flow theories, with the numerically computed forces at a Reynolds number of 5×104. The results show that theoretical scaling can be applied to numerical time-averaged thrust data even in the case of large amplitude motions, and the thrust-prediction law is still applicable to pitching-rotating motions.