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SUMMARY:Evolution of the leading edge vortex over an accelerating rotating
  wing - Elimelech\, Y\, Kolomenskiy\, D\, Moffatt\, HK (Israel Institute o
 f Technology\; CERFACS Toulouse\; DAMTP\,Cambridge)
DTSTART:20120726T134500Z
DTEND:20120726T140500Z
UID:TALK39067@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Flapping flight is a subject of interest for more than two dec
 ades. During this time it has been found that a stable leading edge vortex
  is responsible for the high lift that flapping and revolving wings can pr
 oduce. However\, many of these studies were limited to Reynolds numbers of
  few hundred\, which characterize insects. Recently\, the interest on desi
 gning and realizing miniature hovering vehicles requires expanding our und
 erstanding of the basic flow mechanism which govern such wing maneuvers at
  higher Reynolds numbers. In this study the flow field over an acceleratin
 g rotating wing model is analyzed in various Reynolds numbers ranging from
  250 to 2000 using particle image velocimetry. These experimental results 
 are compared with three-dimensional and time-accurate Navier-Stokes flow s
 imulations. The study depicts the characteristic size and time scales of t
 he leading-edge vortex. The results show that the topology of the leading-
 edge vortex is Reynolds number dependent\; i n comparison to a diffused an
 d detached leading-edge vortex at Reynolds number 250\, at Reynolds number
  2000 the leading-edge vortex is not stationary and can cover up to about 
 75 percent of the local wing chord. Furthermore\, it is shown that the spa
 nwise velocity component increases considerably at Reynolds number of 1000
  and above. Moreover\, in Reynolds number 250 the circulation within the l
 eading-edge vortex during wing acceleration exceeds its asymptotic value w
 hich develops over steadily revolving wings. At Reynolds number 1000 and a
 bove\, on the other hand\, the circulation within the leading-edge vortex 
 evolves much slower. These findings shed new insights about the difference
 s between the aerodynamic characteristics of steady revolving wings and fl
 apping ones and will be utilized to investigate the stability of the leadi
 ng-edge vortex in wider range of Reynolds numbers.\n
LOCATION:Seminar Room 1\, Newton Institute
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