WAKE OF A LOW ASPECT RATIO PITCHING PLATE, St = 0.43
J. H. J. Buchholz and A. J. Smits
A rigid plate of aspect ratio S/C=0.54 (S=span, C=chord)
is pitched in a uniform flow about its leading edge. The
double-amplitude to span ratio is A/S=0.31. The
leading edge is hinged to the trailing edge of a
stationary symmetric 2-D airfoil. Fluorescent dyes are
introduced through a series of holes on each side of the
airfoil support. The Reynolds number based on the
chord of the plate and the freestream velocity U is 640.
Different flow regimes can be identified based on the
Strouhal number, St=fA/U (f=pitching
frequency). Twice in each flapping cycle, a horseshoe
vortex is created, consisting of vorticity shed by the top,
bottom, and trailing edges. At St=0.43 (this image, top and side views), the shed
vorticity splits and forms two distinct branches.
Studying such wakes is believed to be important for
understanding the mechanisms of thrust production in
fish-like swimming. See also St = 0.23 and St = 0.64.
Buchholz, J. H. J. and Smits, A. J., "On the evolution of the wake structure produced by a low aspect-ratio pitching
panel." Journal of Fluid Mechanics, 546, pp. 433-443, 2006.