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Fig. 4. The magnitude and distribution of axial flow is dependent on Re.
The top schematic shows the position of the three side view panels
(0.45R, 0.55R and 0.65R) at each Re. Flows
are captured from a wing at mid-downstroke starting from rest. Columns 1 and 3
show the sectional velocity field as arrows (uy and
ux) superimposed over a pseudo-color plot of axial
velocity (uz). Next to each column are plotted the
ux and uz values along the gray broken
transect from A to B shown in i. The left two columns show flow at low
Re. Note how the maximum axial flow (uz) at low
Re occurs farther behind the vortex center than at high Re.
Also, at high Re, flow near the leading edge is much more
complicated, with a stronger axial flow component.