Efficient flapping foil flow at high Re 2.5 x 10⁵ for large underwater vehicle

The recent development of Autonomous Underwater Vehicles (AUVs) has spurred many studies to understand the efficient swimming performance of animals. Despite these rigorous studies, the propulsive performance of those AUVs is far less efficient than animals. This study explores the possibility of propulsion parameters from animals to be applied at autonomous vehicles using high-fidelity Boundary Data Immersion Method (BDIM) simulations. We find that despite the large leading-edge vortex breakdown on the foil, the flow characteristics are still overpowered by the oscillating kinematics for the optimal Strouhal number range St=[0.2,0.4]. This is due to a laminarization process produced by the flapping motion which was previously reported at lower Reynolds number by Zurman-Nasution et al. [JFM, 2020]. The near-wall flow behavior is presented along with the hydrodynamic forces, providing a detailed explanation of this laminarization behavior. This result allows the dimension-scaling of flapping foil for large underwater vehicles.