SWARTZ, S*; GALVAO, R; IRIARTE-DIAZ, J; ISRAELI, E; MIDDLETON, K; ROEMER, R; TIAN, X; BREUER, K; Brown University; Brown University; Brown University; Brown University; Brown University; Brown University; Brown University; Brown University: Unique characteristics of aerodynamics of bat flight: evidence from direct visualization of patterns of airflow in the wakes of naturally flying bats

The interaction of animal wings with the surrounding fluid is similar to, but quite distinct from, that of the wings of human-engineered aircraft. All animal fliers move their complex, deformable wings, via more or less complicated motions, to produce lift and propulsion. To understand the mechanistic basis of bat flight, we must have detailed information regarding flight forces. One means to achieve this is to employ quantitative flow visualization methods to the structure of the wake footprint left behind flying animals. To visualize and quantify the structure and behavior of the wakes of slow forward flight in Cynopterus brachiotis, we employed Particle Image Velocimetry (PIV). By adapting this technique to naturalistic flight in these bats, we successfully obtained the first detailed, 3D documentation of the structure of bat flight wakes. PIV clearly demonstrates that these wakes differ significantly from those of non-flapping models similar in size and shape to bats, and from those of both flying birds and insects. Bat flight wakes are complex in structure, with many small-scale flow structures in addition to regions of concentrated vorticity. Wake structure changes dynamically over the course of the wingbeat cycle, but does not conform to any published models of flight gaits.