Journal
JOURNAL OF EXPERIMENTAL BIOLOGY
Volume 216, Issue 24, Pages 4567-4579Publisher
COMPANY OF BIOLOGISTS LTD
DOI: 10.1242/jeb.089672
Keywords
von Karman vortex; Manduca sexta; unsteady flows; turbulence; stability; wind tunnel
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Funding
- Air Force Office of Scientific Research grant [FA9550-10-1-006]
- National Science Foundation (NSF) [IOS-0920358, DBI-1152304]
- Direct For Biological Sciences
- Div Of Biological Infrastructure [1152304] Funding Source: National Science Foundation
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Shedding of vortices is a common phenomenon in the atmosphere over a wide range of spatial and temporal scales. However, it is unclear how these vortices of varying scales affect the flight performance of flying animals. In order to examine these interactions, we trained seven hawkmoths (Manduca sexta) (wingspan similar to 9 cm) to fly and feed in a wind tunnel under steady flow (controls) and in the von Karman vortex street of vertically oriented cylinders (two different cylinders with diameters of 10 and 5 cm) at speeds of 0.5, 1 and 2 m s(-1). Cylinders were placed at distances of 5, 25 and 100 cm upstream of the moths. Moths exhibited large amplitude yaw oscillations coupled with modest oscillations in roll and pitch, and slight increases in wingbeat frequency when flying in both the near (recirculating) and middle (vortex dominated) wake regions. Wingbeat amplitude did not vary among treatments, except at 1 m s(-1) for the large cylinder. Yaw and roll oscillations were synchronized with the vortex shedding frequencies in moths flying in the wake of the large cylinder at all speeds. In contrast, yaw and pitch were synchronized with the shedding frequency of small vortices at speeds <= 1 m s(-1). Oscillations in body orientation were also substantially smaller in the small cylinder treatment when compared with the large cylinder, regardless of temporal or non-dimensional spatial scale. Moths flying in steady conditions reached a higher air speed than those flying into cylinder wakes. In general, flight effects produced by the cylinder wakes were qualitatively similar among the recirculating and vortex-dominated wake regions; the magnitude of those effects, however, declined gradually with downstream distance.
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