Propulsion characteristics of self-pitching flapping foil

As a promising form of oscillating hydrofoil propulsion, self-pitching flapping foil (SPFF) has been widely used in ocean engineering applications such as ships, underwater vehicles and ocean energy devices. Due to the complexity of its mass spring system, it is still a lack of comprehensive parametric analysis to conclude the theoretical maximum efficiency of SPFF up to now. Particular interest of this work is centered on the influence of frequency ratio (r), spring stiffness ratio (K & PRIME;), advance coefficient (J) and pitch axis (c0/c) on the propulsive performance of self-pitching flapping foil (SPFF), including induced propulsion force, propulsive efficiency and related wake structure. The analysis covers the range of full advance coefficient, which starts around 0 and ends at a thrust drop of 0. The influence of stiffness ratio (K') on the SPFF performance was discussed in the large range of 0.1-100. Special attention is also paid to the impact of system resonance on performance. By employing an appropriate combination of various parameters, the highest efficiency of SPFF could reach 87.6%, which shows it could perform a satisfactory propulsion performance as a marine propulsion. This study is expected to provide guidance on both academics and industries in relevant fields.