Transient effects during transitions of bio-inspired flapping foils between two different schooling configurations

Recently, there has been considerable interest in developing novel energy-saving vehicles that use flapping foils propulsion systems inspired by biology. Facing increasingly complex application tasks, the coordination of multiple vehicles will be a hot issue in the future this research field. We are inspired by changes in configurations of biological collective behavior (known as schooling) in nature, focused on studying transient effects during transitions of three-dimensional bio-inspired flapping foils between two different bionic schooling configurations. Numerical simulations employing the immersed boundary-lattice Boltzmann method (IB-LBM) for unsteady hydrodynamics of flapping foils in schooling transitions were performed. Effects of different mutual transition modes between tandem and diamond schooling configurations on their thrust performance were investigated. Meanwhile, we present hydrodynamics of flapping foils in a schooling with different downstream flapping frequencies under the best transition mode. The results show that during transitions between two schooling configurations, there is an optimal energy-saving transition mode. It has nothing to do with the length of transition distance. Different downstream flapping frequencies will affect the interacting vortices between fluid and structure and then affect transient effects during schooling transition. Although the transition modes were specified, our research takes the transients effects of schooling transitions as an influencing factor to be considered for formations changes, which will provide a new idea for the design bio-inspired vehicle cluster formation.