Kunihiko, Taira and Colonius, Tim (2009) Three-dimensional flows around low-aspect-ratio flat-plate wings at low Reynolds numbers. Journal of Fluid Mechanics, 623 . pp. 187-207. ISSN 0022-1120 http://resolver.caltech.edu/CaltechAUTHORS:20090629-092825317
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Three-dimensional flows over impulsively translated low-aspect-ratio flat plates are investigated for Reynolds numbers of 300 and 500, with a focus on the unsteady vortex dynamics at post-stall angles of attack. Numerical simulations, validated by an oil tow-tank experiment, are performed to study the influence of aspect ratio, angle of attack and planform geometry on the wake vortices and the resulting forces on the plate. Immediately following the impulsive start, the separated flows create wake vortices that share the same topology for all aspect ratios. At large time, the tip vortices significantly influence the vortex dynamics and the corresponding forces on the wings. Depending on the aspect ratio, angle of attack and Reynolds number, the flow at large time reaches a stable steady state, a periodic cycle or aperiodic shedding. For cases of high angles of attack, an asymmetric wake develops in the spanwise direction at large time. The present results are compared to higher Reynolds number flows. Some non-rectangular planforms are also considered to examine the difference in the wakes and forces. After the impulsive start, the time at which maximum lift occurs is fairly constant for a wide range of flow conditions during the initial transient. Due to the influence of the tip vortices, the three-dimensional dynamics of the wake vortices are found to be quite different from the two-dimensional von Kármán vortex street in terms of stability and shedding frequency.
|Additional Information:||© 2009 Cambridge University Press. Received 18 March 2007 and in revised form 4 November 2008. This work was supported by the US Air Force Office of Scientific Research (FA9550- 05-1-0369) with some of the computations made possible by the US Department of Defense High Performance Computing Modernization Program. We are thankful to Professors C. W. Rowley, M. Gharib, D. R. Williams, G. Tadmor and M. H. Dickinson for the enlightening discussions. Experimental data in § 2.3 were generously shared by Dr W. B. Dickson.|
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|Deposited By:||Tony Diaz|
|Deposited On:||07 Aug 2009 17:50|
|Last Modified:||26 Dec 2012 11:03|
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