Experimental study of flow in wake robotic bird

The Robird is a robotic bird designed and manufactured by the company Clear Flight Solutions. The Robird is inspired by the Peregrine Falcon and mimics the flapping flight of its real-life counterpart. The robotic bird is used to scare off birds by pretending to be a natural enemy. Though this robotic bird proves that flapping flight by a robot is possible, the mechanism behind flapping flight is not fully understood. The goal of the present experimental study is to contribute to a better understanding of flapping wing propulsion of a robotic bird like the Peregrine Falcon based Robird. To that aim a set-up has been designed, realized and utilized for the Silent Wind Tunnel of the University of Twente. The semi span wind tunnel model corresponds to the starboard side of the full-scale robotic bird, capable to operate at realistic conditions of flapping flight in which the wing carries out a combination of a plunge and a pitch motion. In the first part of the study a 21-Pitot-tube wake rake is used to measure profiles of the time-averaged velocity magnitude along traverses downstream of the wind tunnel model for flapping frequencies in the range [2.5-4.0]Hz and free-stream velocities in the range [2.5-7.0]m/s. Utilizing a control-volume analysis then gives an estimate of the time-averaged thrust produced by the robotic bird. The results show that for Strouhal numbers above 0.1 the wake of the flapping wing has, time-averaged, a jet-like streamwise velocity profile, associated with the generation of thrust. For increasing values of the Strouhal number, up to St = 0.45, the maximum value of the jet velocity increases. For Strouhal numbers smaller than 0.27 a jet-like profile is found that is symmetric about the mid position of the flapping wing. For higher values of the Strouhal number the jet-like profile becomes asymmetric.