Meeting Abstract
P1.196 Friday, Jan. 4 Velocity fields in the near-wake of E. fuscus SCHUNK, C.*; CHIU, C.; SWARTZ, S.M.; BREUER, K.S.; Brown University, Providence RI; Brown University, Providence RI; Brown University, Providence RI cosima_schunk@brown.edu
Particle image velocimetry (PIV) in the plane perpendicular to the flight direction (Trefftz plane) provides valuable insight into flight performance and changes in lift generation that occur over the wingbeat cycle in bats. The majority of PIV studies of bat flight have visualized flow in the transverse, or Trefftz plane. However, combining measurements from a parasagittal plane with Trefftz plane measurements allow for a much more detailed understanding of the complex wake structures and can offer an improved understanding of the nature of the temporal evolution of force generation over the wingbeat, as well as the spatial distribution of the aerodynamic force over the wingspan. Here, we present a quantitative description of some of these structures we have observed previously in bat wakes, particularly the strong starting and stopping vortices that appear at the wingtip during the beginning and end of the downstroke. We trained several Big Brown Bats, E. fuscus to fly at a fixed position in the test section of a wind tunnel at wind speeds between 4.5 m/s and 7 m/s. We measured the air flow around the left wing of the bat and in the wake immediately behind it using time-resolved (200 Hz) stereo PIV. In addition, three high-speed cameras (400 Hz) captured the position and movement of the bat to reconstruct wing kinematics. We captured the wake over multiple consecutive wingbeats. Differences in the pattern and strength of starting and stopping vortices suggest that early in downstroke, as lift generation begins, the site of primary lift production travels gradually from the wingroot to the wingtip and the termination of lift generation at the end of the downstroke is sudden. This pattern may be unique in flying animals studied to date. Research supported by AFOSR.
