Journal of Fluid Mechanics
- Journal of Fluid Mechanics / Volume 733 / October 2013, R5 (13 pages)
- ©2013 Cambridge University Press. This is a work of the U.S. Government and is not subject to copyright protection in the United States.
- DOI: http://dx.doi.org/10.1017/jfm.2013.444 (About DOI), Published online: 26 September 2013
Rapids
Unsteady pitching flat plates
Kenneth O. Granlunda1 c1, Michael V. Ola1 and Luis P. Bernala2
a1 Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, USA
a2 Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109, USA
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.
(Received June 05 2013)
(Revised July 31 2013)
(Accepted August 19 2013)
Key words
- low-dimensional models;
- nonlinear dynamical systems;
- separated flows;
- vortex flows;
- wakes/jets
Correspondence
c1 Email address for correspondence: kenneth.granlund@wpafb.af.mil
