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On the distribution of leading-edge vortex circulation in samara-like flight

Published online by Cambridge University Press:  10 July 2015

Eric Limacher  and
David E. Rival
Eric Limacher*
Affiliation:
Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB, T2L 1Y6, Canada
David E. Rival
Affiliation:
Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB, T2L 1Y6, Canada Department of Mechanical and Materials Engineering, Queen’s University, Kingston, ON, K7L 3N6, Canada
*
†Email address for correspondence: [email protected]
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Abstract

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.

JFM classification

Biological Fluid Dynamics: Biological Fluid Dynamics Vortex Flows: Vortex Flows
Type
Papers
Information
Journal of Fluid Mechanics , Volume 776 , 10 August 2015 , pp. 316 - 333
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Copyright
© 2015 Cambridge University Press 

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Limacher supplementary movie

Dye visualization videos at four tip speed ratios (increasing from left to right), and two fixed inclination angles of the flat plate relative to the swept disk (τ = 0 and 20 degrees). Purple streaklines of dye emanate from a port 1mm from the leading edge on the pressure side of the plate. The streakline is observed to draw closer to the suction side of the plate with increasing tip speed ratio, and clearly stagnates onto the suction side of the plate at the highest tip speed ratio. Span-wise flow also becomes more prominent as tip speed ratio increases.

Download Limacher supplementary movie(Video)
Video 4 MB