On the dynamics of a tandem of asynchronous flapping wings: Lattice Boltzmann-immersed boundary simulations

In this paper, the flight performance of a tandem of symmetric flapping wings immersed in a viscous fluid is investigated. A harmonic motion is imposed to the wings which can travel only in the vertical direction. Specifically, the attention focuses on the role of the initial phase difference. The fluid domain is modeled through the lattice Boltzmann method. In order to account for the presence of the wings immersed in the lattice fluid background, the immersed boundary method is adopted. Once fluid forces acting upon the wings are computed, their position is updated by solving the equation of solid motion by the time discontinuous Galerkin method according to a strategy already validated by the author. A wide numerical campaign is carried out by varying the initial phase difference. Moreover, scenarios accounting for the presence of a lateral wind gust are shown. The flight conditions and performance are discussed for a wide set of configurations and compared with an in-sync configuration, showing that the wind gust reduces the performance in certain scenarios.