Meeting Abstract
The interaction between turbulence and bird flight is presented using three types of birds: European Starling (Sturnus vulgaris), Western Sandpiper (Calidris mauri), and American Robin (Turdus migratorius) at The Advanced Facility for Avian Research, Western University, Ontario, Canada. The near wake of freely flying birds was measured using high speed, time-resolved, particle image velocimetry (PIV), simultaneously with imaging the wing kinematics, using high-speed cameras. The system samples the flow field continuously for 20 minutes, which enables us to capture the wake evolution over multiple flap cycles. The acquired PIV images were used to generate vector maps, which combined with the wings’ kinematic images, enable the association of the near wake features with the wing configuration and bird’s location in the wind tunnel. Time series of the vorticity fields have been expressed as composite wake plots, which depict segments of the wing beat cycle for various span-wise locations in the wake. The composite wake plots reveal various characteristics of the wake during the upstroke (US) and downstroke (DS) phase of the flapping as well as the transition between the US to DS and vice versa. In addition, some of the features presented are the result of stream-wise vortices interacting in the wake. Comparison between the near wake fields behind the three birds reveals remarkable similarity in their wake structure. We have identified over multiple wingbeat cycles the presence of what appears to be an inclined vortex ring, generated during the upper half of the wing beat cycle. The compositions of the measured vorticity fields provide a quantitative description of the vortex ring and other flow patterns.
