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UID:6451@i2m.univ-amu.fr
DTSTART;TZID=Europe/Paris:20210414T090000
DTEND;TZID=Europe/Paris:20210414T100000
DTSTAMP:20241120T201436Z
URL:https://www.i2m.univ-amu.fr/evenements/aerodynamics-of-dragonfly-fligh
 t-impact-of-wing-kinematics-and-morphology/
SUMMARY:Xiaohui Liu (Department of Mechanical and Aerospace Engineering\, T
 he Hong Kong University of Science and Technology\, Hong Kong Special Admi
 nistrative Region of China): Aerodynamics of dragonfly flight: impact of w
 ing kinematics and morphology
DESCRIPTION:Xiaohui Liu: Micro air vehicles (MAVs) are operated in the size
  region under the same environmental conditions as natural flyers. Insects
  are a good teacher for bioinspired designs of MAVs\, and dragonflies are 
 highly aerobatic insects having high aspect ratio wings in tandem. The for
 ewing and the hindwing of a dragonfly have different geometry that could b
 e an evolutionary specialization for better aerodynamic performance via so
 phisticated wing pitch control. Firstly\, the dragonfly wing surface struc
 ture is reconstructed with FTP\, and the wing deformation under two differ
 ent wing speed are measured. It shows that dragonfly wing is corrugated ov
 er the whole surface\, especially in the root and leading-edge region. Com
 pare with forewing\, the hindwing is easier to occur chord deformation due
  to larger chord length. Secondly\, we measured the flow around the flappi
 ng wings using time-resolved particle image velocimetry (TR-PIV) to invest
 igate the consequences of shape and the pitching mechanisms of the wings o
 n the aerodynamics of dragonflies. The flow fields and pitching angle vari
 ations of the naturally actuated wing of the dragonfly were compared with 
 that of the same wing artificially actuated only by flapping motion. We fo
 und that the trailing edge vortex dynamics and the wake were affected by t
 he wing shape only for the in-vivo experiment with muscle induced pitching
 . Under the in-vivo with muscle induced pitching\, the hindwing took more 
 part in generating horizontal momentum with larger pitching magnitude\, du
 e to the larger chord length compared with forewing. Meanwhile\, when ther
 e was only pitching due to the wing membrane deformation of artificially a
 ctuated flapping\, a slight difference in the surrounding flow structures 
 was found between the hindwing and the forewing\, and the net flow in one 
 period was reduced nearly to zero. Thirdly\, we measured the kinematic par
 ameters of the wings in two different flight modes (normal flight mode (NF
 M) and escape flight mode (EFM)). When the specimens switched from normal 
 to escape mode the flapping frequency was invariant\, but the stroke plane
  of the wings was more horizontally inclined. The flapping of both wings w
 as adjusted to be more ventral with a change of the pitching angle that re
 sulted in a larger angle of attack during downstroke and smaller during up
 stroke to affect the flow directions and the added mass effect. Noticeably
 \, the phasing between the fore and hind pair of wings varies between two 
 flight modes. It is found that the momentum stream in the wake of EFM is q
 ualitatively different from that in NFM. The change of the stroke plane an
 gle and the varied pitching angle of the wings diverts the momentum downwa
 rds\, while the smaller flapping amplitude and less phase difference betwe
 en the wings compresses the momentum stream.\nIOSSB Seminar
CATEGORIES:Interdisciplinary online seminar series on
 Biolocomotion,Virtual event
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