Propulsive performance analysis of a full-active rotating flapping foil

The conventional heaving flapping-foil propulsion system, which couples heaving and pitching motions, shows considerable application potential in the field of underwater propulsion owing to its performance advantages. To further advance underwater propulsion technology, this study proposes a fully active rotating flapping foil propulsion device with compound rotating–pitching motion. A three-dimensional flapping foil of a National Advisory Committee for Aeronautics (NACA) section 0012, subjected to coupled rotating and pitching motions, is simulated using the finite volume method, the sliding mesh technique, and user-defined functions. The research analyzes the effects of maximum angular displacement, pitching amplitude, and nominal rotational speed on its propulsive performance. Results indicate that increasing the maximum angular displacement can effectively enhance the thrust generated by the rotating flapping foil. However, with the increase in pitching amplitude, the mean thrust coefficient of the rotating flapping foil first increases and then decreases, suggesting that an optimal pitching amplitude exists for the rotating flapping foil propulsion system. Further analysis was conducted on the effect of nominal rotational speed on the propulsive performance of the rotating flapping foil. It was found that the nominal rotational speed exhibits a positive correlation with the generated thrust: the higher the nominal rotational speed, the greater the thrust output of the rotating flapping foil. Furthermore, compared with conventional heaving flapping foils, the rotating flapping foil achieves a 22.5% increase in thrust under identical operational conditions. The full-active rotating flapping foil proposed in this study exhibits excellent hydrodynamic performance, paving a new way to develop underwater propulsion technology.