How Wingbeat Kinematics Affect the Wake Structure of a Flapping Wing Robot

The aerodynamic wake of a flier such as a bird or bat encodes the history of the force output of the flier. Additionally, it will impart forces and moments on a flier behind the lead flier. It's unclear how the structure of the wake is influenced by wingbeat kinematics, and here we aim to explore this question systematically with a flapping robot. We perform PIV behind a flapping robot mounted in a wind tunnel test section, and operating at a range of wingbeat frequencies (0 - 10 Hz), flapping amplitudes (10 - 30°, measured peak-to-centerline), and wind speeds (4 - 6 m/s). The robot uses a single DoF flapping motion, but the wings pitch passively due to deformation of the wing membrane. The PIV measurements are compared with the mechanical power required to generate the prescribed kinematics and the aerodynamic forces, measured using a force sensor.