Spanwise length and mesh resolution effects on simulated flow around a 5:1 rectangular cylinder

Zhang, Zhanbiao; Fei, Xu

doi:10.1016/j.jweia.2020.104186

Cited by 22 publications

(5 citation statements)

References 27 publications

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“…This may be due to the inevitable difference of 2D numerical simulation. Previous studies (Bruno et al 2012, Zhang et al 2020 have also shown that insufficient spanwise mesh resolution results in a slight decrease in St. Compared with the results of DNS (Trais et al 2015), the St value of the present simulation is about 3% smaller, which is completely acceptable.…”

Section: Grid Independency Studysupporting

confidence: 45%

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

Wu¹,

Liu²,

Zhang³

et al. 2023

Fluid Dyn. Res.

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RANS simulations are performed for flow past rectangular cylinders with different elongation ratios (L/D=1, 2, 4, 6, 8, 10, 12, 14 and 16) at Re=22000 using the k-ω SST turbulence model. As L/D increases from 1 to 6, stepwise increase of Strouhal number (St) exists, whereas an almost linear variation of St with respect to L/D can be found (St=0.1618*L/D) at L/D≥8. In the flow, two small secondary vortices beneath the shear layers are identified and the trailing-edge secondary vortex presents opposite rotational direction comparing with the leading-edge main vortex. Analysis of the shear layer and vortex characteristics is carried out to correlate with the wall normal stress and shear stress on the rectangular cylinder surfaces. Further, four coupling modes between leading-edge vortex (L-vortex) and trailing-edge vortex (T-vortex) among cylinders with different L/D are observed, named L-Vortex Mode (i.e. L/D=1~2), L-T-Vortex Mode (i.e. L/D=4~8), T-L-Vortex Mode (i.e. L/D=10~14), and T-Vortex Mode (i.e. L/D≥16). When L/D>4, the convective velocity of the L- and T-vortex is not sensitive to the L/D.

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Section: Grid Independency Studysupporting

confidence: 45%

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

Wu¹,

Liu²,

Zhang³

et al. 2023

Fluid Dyn. Res.

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“…It is known that mesh resolution, in both the x – y plane and the spanwise direction, and the spanwise domain size may have significant influences on the simulated flow around a rectangular prism (Bruno, Coste & Fransos 2012; Zhang & Xu 2020). In the present study, a mesh dependence study is performed.…”

Section: Numerical Modelmentioning

confidence: 99%

Global instability and mode selection in flow fields around rectangular prisms

et al. 2023

Self Cite

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Large-eddy simulations of the unsteady flows around rectangular prisms with chord-to-depth ratios (B/D) ranging from 3 to 12 are carried out at a Reynolds number of 1000. A particular focus of the study is the physical mechanisms governing the global instability of the flow. The coherent structures and velocity spectra reveal that large-scale leading-edge vortices (L vortices) are formed by the coalescence of Kelvin–Helmholtz rollers. Based on dynamic mode decomposition, the interactions between the L vortex and the trailing-edge vortex (T vortex) at different B/D values are revealed. It is found that the phase difference between the L and T vortices is the critical factor promoting a stepwise increase in the Strouhal number with increasing B/D. According to the phase analysis, there are two types of pressure feedback-loop mechanisms maintaining the self-sustained oscillations. When B/D = 4–5, the feedback loop covers the separation region, and the global instability is controlled by the impinging shear-layer instability. When B/D = 3 and 6–12, the feedback loop covers the entire chord, and the global instability is controlled by the impinging leading-edge vortex shedding instability. Self-sustained oscillations of the shear layer still exist after a splitter plate is placed in the near wake, indicating that the T vortex shedding is not essential in triggering the global instability. Nevertheless, with the participation of the T vortex, the primary instability mode may be reselected due to the upper and lower limits of the shedding frequency imposed by the T vortex.

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“…The 3D flow field around the cylinder can also be studied based on the instantaneous vortex structures, which can be identified by the second invariant Q (Zhang and Xu, 2020):where, S=12(∂ui∂xj+∂uj∂xi) is symmetric component of ∇U, and Ω=12(∂ui∂xj−∂uj∂xi) is an antisymmetric one; and ∇ represents the Hamiltonian operator. The shear strain rate and vorticity magnitude are well balanced by Q .…”

Section: Resultsmentioning

confidence: 99%

“…The shear strain rate and vorticity magnitude are well balanced by Q . A positive value of Q represents rotational flow, and a higher value corresponds to a higher vortex intensity (Zhang and Xu, 2020). Therefore, the Q criterion is significantly better than the vorticity criteria for extracting the vortices around the cylinder and C-ring.…”

Section: Resultsmentioning

confidence: 99%

Numerical study on aerodynamic characteristics and flow field of a circular cylinder equipped with a C-ring behind at Re = 1000

Jing

Zhang

2023

Advances in Structural Engineering

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Slender cylindrical structures such as cables and signal poles often experience vortex-induced vibrations. Recently, scholars have developed a novel mitigating measure by equipping a C-ring on the structures, where the C-ring is always behind the cylinder by tail rudder, but the mitigation mechanism is still unclear. To this end, the OpenFOAM©, an open source software, has been adopted in this study to carry out the large-eddy simulations (LES) to investigate the influence of a C-ring on the aerodynamic forces, surface pressure, and flow around a circular cylinder at Re = 1000, where the dynamic k-equation LES model is employed. Although the Re is far smaller than that in the reality, the aerodynamic characteristics and flow is also representative and worth studying in this subcritical range. Furthermore, to determine the appropriate radii ( R) and arc lengths ( θ) of the C-ring, various values of R (0.7 D, 0.8 D, 0.9 D, and 1.0 D, where D is diameter of the cylinder) and θ (60°, 90°, 120°, 150°, and 180°) are considered and studied herein. The results indicate that a C-ring can reduce the SD of the lift coefficient by 40%–90% compared to that of a bare cylinder, whereas it has an unremarkable effect on the mean drag coefficient. The C-ring also has a significant influence on the fluctuating pressure coefficients, resulting in a small SD of the fluctuating lift. The spanwise flow on the leeward side of the cylinder under the influence of C-rings with different radii and arc lengths can be categorized into three modes. Meanwhile, the C-ring mitigates wind-induced vibrations by enhancing the spanwise flow on the leeward side of the cylinder. Finally, the appropriate parameters for the C-ring are recommended as follows: R = 0.7 D and θ = 180°; R = 0.8 D and θ = 150°; R = 0.9 D and θ = 150°; R = 1.0 D and θ = 120°, 150°.

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Spanwise length and mesh resolution effects on simulated flow around a 5:1 rectangular cylinder

Cited by 22 publications

References 27 publications

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

Global instability and mode selection in flow fields around rectangular prisms

Numerical study on aerodynamic characteristics and flow field of a circular cylinder equipped with a C-ring behind at Re = 1000

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