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Vortex evolution in the near wake behind polygonal cylinders.

Wang, Qingyang and Gan, Lian and Xu, Shengjin and Zhou, Yu (2020) 'Vortex evolution in the near wake behind polygonal cylinders.', Experimental thermal and fluid science., 110 . p. 109940.


The near wake of the polygonal cylinder with the side number N = 3~∞ is systematically studied using particle image velocimetry (PIV) at Re = 1.6 × 104. The proper orthogonal decomposition (POD) analysis is carried out to extract the large-scale coherent vortex structures and their evolution. It has been found that the vortex circulation grows to the maximum at the vortex formation length by entraining the vorticity from the separated shear layer and then undergoes a two-stage decay. The maximum circulation scales with the wake width, defined as the vertical distance between the two peaks of streamwise velocity fluctuation at vortex formation length. The vortex center trajectory indicates that the vortices move towards the centerline first and then away, with the vortex size monotonically increasing over the examined streamwise range. The vortex size at the maximum circulation also scales with the wake width. The vortex convection velocity increases gradually in the streamwise direction, and the ratio of the lateral and streamwise components of the vortex convection velocity, when scaled by wake width and vortex formation length respectively, approaches asymptotically 0.18 in the downstream, irrespective of the cylinder orientation or N.

Item Type:Article
Full text:(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Publisher statement:© 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Date accepted:22 September 2019
Date deposited:11 October 2019
Date of first online publication:23 September 2019
Date first made open access:23 September 2020

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