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Fig. 9. Schematic reconstruction of wake pattern during wing–wake interaction
in fruit fly model wings and effect of heaving motion during clap-and-fling.
(A,B) The graphs show chordwise wing segments during clap-and-fling at the end
of the upstroke, during the clap, and during the fling phase before the two
wings separate for the downstroke. The low-pressure region evolving between
the wings during the fling pulls fluid around the leading and the trailing
wing edge into the opening cleft. Inflow of fluid during fling potentially
increases during heaving down motion, as shown in A, and decreases when the
wings move upwards at the beginning of the downstroke, as shown in B (cf.
length of black straight arrows). (C) Simplified hypothetical analytical
simulation modelling the inflow velocity between both leading wing edges
during fling. Angular velocity during dorsal wing rotation and wing size are
taken from a tethered flying fruit fly. The model predicts a reduction in flow
velocities into the opening cleft during upward heaving motion whereas flow
velocity increases during downward heaving compared to a wing beat without
heaving motion (blue). (D) Heaving rate and direction plotted against vertical
force augmentation during clap-and-fling wing beat. Pictogram illustrates the
change in stroke angle (
, black), the wing's angle of attack
(
m, blue) and heaving angle (
, green). Heaving rate
was derived from the angular change within a time window of 0.1 stroke cycle
after the wing has started the downstroke. (E) Effect of heaving up and down
motion during fling on vertical force coefficient of a single wing (left),
absolute vertical force augmentation when flapping both wings (middle) and
relative vertical force augmentation due to clap-and-fling (right). NS, not
significant; ***P<0.001 significance level.
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