Meeting Abstract

70.4  Tuesday, Jan. 6  Computational modeling of the aeromechanics of a bat (Cynopterus brachyotis) WILLIS, D.J.*; RISKIN, D.K.; SWARTZ, S.M.; PERAIRE, J.; BREUER, K.S.; Univ. Massachusetts, Lowell; Brown Univ.; Brown Univ.; Massachusetts Institute of Technology; Brown Univ. david_willis@uml.edu

Bat flight represents a complex interaction between unsteady fluid flow and the material that composes the wing. Here, we explore bat flight aeromechanics using a computational model that exploits accurate, high resolution, in flight kinematics recordings of a bat (Cynopterus brachyotis). Using accurate reconstructions of the wing geometry, we apply a computational aerodynamics panel method to model the flow around the wings and in the wake region of the bat to hypothesize aerodynamics forces, wing surface pressure distributions, and wake vorticity distributions. As a first check of our results, we compare the time series of lift forces from our model to the accelerations of the bat body, estimated by taking into account wing inertial effects. The force predictions from the computational aerodynamics model and the estimated center of mass accelerations are compared and are found to be in good agreement. Our methods produce a hypothesized flow structure behind the bat consisting of a wake that is composed of discrete vortex rings, suggesting a down-stroke dominated flight strategy. The main difference that was observed between fast and slow flight was the change in the pressure jump distribution over the wings. In slow flight, the predicted loading is greater in the distal regions of the wing, while in fast flight the predicted loading tends to be closer to the proximal regions of the wing. This shift in loading is accompanied by large forward-aft flapping motions in slow flight and reduced forward-aft excursions in fast flight.