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Unsteady pitching flat plates

Published online by Cambridge University Press:  26 September 2013

Kenneth O. Granlund ,
Michael V. Ol  and
Luis P. Bernal
Kenneth O. Granlund*
Affiliation:
Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, USA
Michael V. Ol
Affiliation:
Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, USA
Luis P. Bernal
Affiliation:
Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109, USA
*
†Email address for correspondence: kenneth.granlund@wpafb.af.mil
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Abstract

Direct force measurements and qualitative flow visualization were used to compare flow field evolution versus lift and drag for a nominally two-dimensional rigid flat plate executing smoothed linear pitch ramp manoeuvres in a water tunnel. Non-dimensional pitch rate was varied from 0.01 to 0.5, incidence angle from 0 to 90°, and pitch pivot point from the leading to the trailing edge. For low pitch rates, the main unsteady effect is delay of stall beyond the steady incidence angle. Shifting the time base to account for different pivot points leads to collapse of both lift/drag history and flow field history. For higher rates, a leading edge vortex forms; its history also depends on pitch pivot point, but linear shift in time base is not successful in collapsing lift/drag history. Instead, a phenomenological algebraic relation, valid at the higher pitch rates, accounts for lift and drag for different rates and pivot points, through at least 45° incidence angle.

JFM classification

Nonlinear Dynamical Systems: Low-dimensional models Nonlinear Dynamical Systems: Nonlinear Dynamical Systems Wakes/Jets: Separated flows Vortex Flows: Vortex Flows Wakes/Jets: Wakes/Jets
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 733 , 25 October 2013 , R5
Creative Commons
This is a work of the U.S. Government and is not subject to copyright protection in the United States.
Copyright
©2013 Cambridge University Press.

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Granlund et al. supplementary movie

Flowfield of pitching plate, pivoting around the leading edge at reduced frequency of K=0.2

Download Granlund et al. supplementary movie(Video)
Video 9.1 MB

Granlund et al. supplementary movie

Flowfield of pitching plate, pivoting around the trailing edge at reduced frequency of K=0.2

Download Granlund et al. supplementary movie(Video)
Video 3.9 MB

Granlund et al. supplementary movie

Flowfield of pitching plate, pivoting around the leading edge at reduced frequency of K=0.03

Download Granlund et al. supplementary movie(Video)
Video 7.8 MB

Granlund et al. supplementary movie

Flowfield of pitching plate, pivoting around the trailing edge at reduced frequency of K=0.03

Download Granlund et al. supplementary movie(Video)
Video 6.4 MB