Meeting Abstract

42.4  Tuesday, Jan. 5  Unsteady forces occur at ventral stroke reversal in the hawkmoth, Manduca sexta MOUNTCASTLE, A.M.*; DANIEL, T.L.; University of Washington, Seattle; University of Washington, Seattle mtcastle@u.washington.edu

Insect wings are compliant structures that often yield to aerodynamic and inertial-elastic loads during flapping flight. In the hawkmoth, Manduca sexta, deformations of the wings are most extreme at ventral stroke reversal as they undergo a rapid pitch reversal and substantial spanwise bending. Although the extent to which such deformations affect flight forces in insects remains generally unknown, prior results show a significant aerodynamic consequence of wing flexibility, with greater induced flows for more compliant wings. The mechanisms underlying this difference, however, are unclear. To explore this issue, we combined computational and experimental approaches to examine the forces and flow fields associated with flapping compliant wings. We use a 2-dimensional ideal flow simulation of flapping wings. This simulation derives from a distribution of sources of vorticity (vortexlets) whose combined strengths determine the flow field around them. That flow field, in turn, is used to predict both steady and unsteady aerodynamic forces. We track wing kinematics of a hovering moth and model a series of chord-wise sections with waveform equations that describe their pitching motion relative to the rigid leading edge of the wing. Our results show that the rapid pitch reversal at ventral stroke reversal itself generates an impulse that is 5-10% of the total impulse required to support the animal’s weight over an entire wing stroke. Furthermore, the forces generated during pitching in this time domain increase with pitch amplitude. These results are consistent with our prior experimental findings and suggest that transient forces arising at stroke reversals play an important role in insect flight.