Transient Force on a Rotating AR 2 Semi-Span Flat Plate

Transient forces are measured on an aspect ratio 2 semi-span flat plate rotating about its long axis (at mid-chord) across a variety of tip speed ratios (reduced frequencies). The flat plate is used as an oversimplified surrogate to Savonius-type vertical axis wind turbines. Little is presently understood about the process or importance of vortex formation and shedding throughout the rotational cycle of vertical axis wind turbines. Rotating a thin flat plate reduces ambiguity due to Reynolds number effects on the initial formation of vortices. Parametrically varying tip speed ratio highlights the influence of vortex convective time on transient force. This experiment provides an interesting bridge between the flowfields associated with flapping wings and vertical axis wind turbines. Parallels will be drawn between the two by comparing recent work in both fields. At the low reduced frequencies tested, static flat plate theory does an excellent job of describing the lift and drag from 45 degrees to 145 degrees angle of attack. Lifting surface theory described the lift curve slope well in the linear region up to stall inception