As an abstraction of natural samara flight, steadily rotating plates in a free-stream flow have been studied. Particle image velocimetry on span-normal planes has been conducted to show that increasing rotation, as captured by the dimensionless parameter of tip speed ratio, causes a transition of the mean wake topology from that of a bluff body to that of a stable leading-edge vortex. Despite its notable effect on topology, a change in tip speed ratio has negligible effect on leading-edge circulation at a given spanwise position, local effective angle of attack and local effective velocity. The effective angle-of-attack distribution was held constant at different tip speed ratios by comparing rotating plates with different twist profiles. The shear-layer velocity profile at the leading edge was also resolved, allowing quantification of the vorticity flux passing through the leading-edge shear layer. Interestingly, the observed equilibrium values of circulation are not sensitive to changes in shear-layer vorticity flux.
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