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 (u_y and u_x) superimposed over a pseudo-color plot of axial velocity (u_z). Next to each column are plotted the u_x and u_z 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 (u_z) 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.