Secondary vortex dynamics in the cylinder wake during laminar-to-turbulent transition

Jeffrey McClure, Colin Pavan, and Serhiy Yarusevych
Phys. Rev. Fluids 4, 124702 – Published 24 December 2019
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Abstract

Direct numerical simulations of cross-flow over a circular cylinder are performed for Re=100, 220, 300, 800, and 1575, spanning laminar-to-turbulent transition and progressively capturing the initial two-dimensional global instability, three-dimensional mode A* and mode B instabilities, a distinct B+ instability, and Kelvin-Helmholtz instability, respectively. For Re800, vortex topology and snapshot proper orthogonal decomposition (sPOD) analyses of the three-dimensional flow fields reveal significant alterations in the dynamics of secondary vortices preceding shear layer transition, denoted B+ instability. The defining instantaneous characteristic of B+ instability is hairpin vortex formations straddling mode B structures. An iterative scheme for three-dimensional vortex tracking is employed and the probability density functions of secondary vortex statistics show a marked broadening for Re800, associated with the increased variability in the wake vortex dynamics. The significant broadening of the modal energy spectrum of the sPOD serves as a marker for the topological change to B+ instability, reflecting the increased complexity of the dynamics. Integral effects on the primary shedding instability due to the increase in secondary vortex formation are deduced through a decomposition of the vorticity transport in the wake. An increase in streamwise and transverse reorientation of spanwise vorticity is identified for increasing Re, leading to a decrease of up to 20% in the advected spanwise vorticity of the primary vortices. Therefore, the reorientation of spanwise vorticity may be identified as a subsidiary mechanism for the attenuation of fluctuating structural loads in the basic cylinder wake.

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  • Received 15 October 2018

DOI:https://doi.org/10.1103/PhysRevFluids.4.124702

©2019 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

Jeffrey McClure*, Colin Pavan, and Serhiy Yarusevych

  • Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario N2L3G1, Canada

  • *jejmcclu@uwaterloo.ca

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Issue

Vol. 4, Iss. 12 — December 2019

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