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A computational investigation of the instability of the detached shear layers in the wake of a circular cylinder

Published online by Cambridge University Press:  15 July 2010

MAN MOHAN RAI
MAN MOHAN RAI*
Affiliation:
NASA Ames Research Center, Moffett Field, CA 94035, USA
*
†Email address for correspondence: man.m.rai@nasa.gov
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Abstract

Cylinder wakes have been studied extensively over several decades to better understand the basic flow phenomena encountered in such flows. The physics of the very near wake of the cylinder is perhaps the most challenging of them all. This region comprises the two detached shear layers, the recirculation region and wake flow. A study of the instability of the detached shear layers is important because these shear layers have a considerable impact on the dynamics of the very near wake. It has been observed experimentally that during certain periods of time that are randomly distributed, the measured fluctuating velocity component near the shear layers shows considerable amplification and it subsequently returns to its normal level (intermittency). Here, direct numerical simulations are used to accomplish a number of objectives such as confirming the presence of intermittency (computationally) and shedding light on processes that contribute significantly to intermittency and shear-layer transition/breakdown. Velocity time traces together with corresponding instantaneous vorticity contours are used in deciphering the fundamental processes underlying intermittency and shear-layer transition. The computed velocity spectra at three locations along the shear layer are provided. The computed shear-layer frequency agrees well with a power-law fit to experimental data.

JFM classification

Instability: Instability Mathematical Foundations: Mathematical Foundations Wakes/Jets: Wakes/Jets
Type
Papers
Information
Journal of Fluid Mechanics , Volume 659 , 25 September 2010 , pp. 375 - 404
Creative Commons
This is a work of the U.S. Government and is not subject to copyright protection in the United States.
Copyright
Copyright © Cambridge University Press 2010 This is a work of the U.S. Government and is not subject to copyright protection in the United States.

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References

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Rai Supplementary Movie

Animation shows initiation of major breakdown of upper shear layer caused by interaction between shear layer and ingested vortices. Animation also shows minor disruption of lower shear layer caused by similar interaction followed by reestablishment of quiescent state. T=6.1 through 6.9 shedding cycles, k = 8 (see Fig. 17). One frame per 40 time steps.

Download Rai Supplementary Movie(Video)
Video 13.3 MB