Vortex evolution in the near wake behind polygonal cylinders

Wang, Qingyang; Gan, Lian; Xu, Shengjin; Zhou, Yu

Abstract

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.

Citation

Wang, Q., Gan, L., Xu, S., & Zhou, Y. (2020). Vortex evolution in the near wake behind polygonal cylinders. Experimental Thermal and Fluid Science, 110, Article 109940. https://doi.org/10.1016/j.expthermflusci.2019.109940

• Journal Article Type: Article
• Acceptance Date: Sep 22, 2019
• Online Publication Date: Sep 23, 2019
• Publication Date: Jan 31, 2020
• Deposit Date: Oct 11, 2019
• Publicly Available Date: Sep 23, 2020
• Journal: Experimental Thermal and Fluid Science
• Print ISSN: 0894-1777
• Electronic ISSN: 1879-2286
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 110
• Article Number: 109940
• DOI: https://doi.org/10.1016/j.expthermflusci.2019.109940
• Public URL: https://durham-repository.worktribe.com/output/1318402