Hydrodynamic characteristics and performance of the 3-DoF three-phase motion of hydrofoil inspired by sea lion foreflipper

As ocean exploration deepens, new demands on propulsion methods are proposed due to the complex underwater environments. Marine animals exhibit excellent locomotion properties, which provide a promising direction for the development of high-performance underwater robots. The unique hydrofoil-paddle propulsion mode of the sea lions foreflippers is a key contributor to their efficient locomotion. Inspired by this, the present work simulates the hydrofoil motion of California sea lion foreflippers with a transient computational fluid dynamic model using dynamic mesh technology to investigate its hydrodynamic characteristics and performance. The result shows that thrust generation during the recovery and power phases is dominated by lift-based propulsion, while during the paddle phase it is dominated by drag-based propulsion. Maximum thrust in a stroke cycle occurs in the power phase, while maximum efficiency at the same motion speed of the hydrofoil is achieved in the paddle phase. The effects of the motion parameters, including Strouhal number (St) and the dimensionless flapping amplitude (h), on the hydrodynamic performance are also investigated. Analysis results show that the optimal thrust and efficiency are achieved in the St range of [0.220, 0.293] and h range of [1.0, 1.864], with the highest efficiency of 25.27% occurring at St = 0.293 and h = 1.846. The present work provides valuable theoretical guidance for designing the bionic robotic foreflippers.