Simulation of flapping bird flight: closed-loop control, forces and wake topology

Colognesi, Victor [UCL] et al.

This work aims at reproducing bird flight in silico in order to shed light on its performance-enabling mechanisms. To that end, we establish an anatomical model of a bird with a pure flapping gait, the bald ibis. It combines a multibody model of the skeleton, with the corresponding joints and degrees of freedom, and a plumage model. The latter allows extracting the wing geometry and aerodynamic properties for any configuration of the skeleton. These properties are translated into a deforming immersed lifting line, which handles the sources of vorticity within a vortex particle-mesh method. The resulting multiphysics framework captures, at a high fidelity, the full flight dynamics, the required efforts and the resulting wake. A sensitivity analysis is carried out and leveraged for the design of a flight controller. Specifically, we quantity the influence of shoulder kinematic features on the aerodynamic forces and moments. The controller then uses these features as command parameters. This bird model can reach a trimmed state over various flight regimes and can handle transients between them. Finally, the accurate capture of the wake vortical structures allows their unambiguous identification and association with the time-varying aerodynamic forces produced by the bird.