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Research Papers: Fundamental Issues and Canonical Flows

Flow Unsteadiness and Stability Characteristics of Low-Re Flow Past an Inclined Triangular Cylinder

[+] Author and Article Information
Wei Zhang

Faculty of Mechanical Engineering
and Automation,
Zhejiang Sci-Tech University,
Hangzhou, Zhejiang 310018, China
e-mail: zhangwei@zstu.edu.cn

Hui Yang

Faculty of Mechanical Engineering
and Automation,
Zhejiang Sci-Tech University,
Hangzhou, Zhejiang 310018, China
e-mail: yanghui@zstu.edu.cn

Hua-Shu Dou

Faculty of Mechanical Engineering
and Automation,
Zhejiang Sci-Tech University,
Hangzhou, Zhejiang 310018, China
e-mail: huashudou@yahoo.com

Zuchao Zhu

Faculty of Mechanical Engineering
and Automation,
Zhejiang Sci-Tech University,
Hangzhou, Zhejiang 310018, China
e-mail: zhuzuchao@zstu.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 16, 2017; final manuscript received June 16, 2017; published online September 1, 2017. Assoc. Editor: Praveen Ramaprabhu.

J. Fluids Eng 139(12), 121203 (Sep 01, 2017) (14 pages) Paper No: FE-17-1099; doi: 10.1115/1.4037277 History: Received February 16, 2017; Revised June 16, 2017

The present study investigates the two-dimensional flow past an inclined triangular cylinder at Re = 100. Numerical simulation is performed to explore the effect of cylinder inclination on the aerodynamic quantities, unsteady flow patterns, time-averaged flow characteristics, and flow unsteadiness. We also provide the first global linear stability analysis and sensitivity analysis on the targeted physical problem for the potential application of flow control. The objective of this work is to quantitatively identify the effect of cylinder inclination on the characteristic quantities and unsteady flow patterns, with emphasis on the flow unsteadiness and instability. Numerical results reveal that the flow unsteadiness is generally more pronounced for the base-facing-like cylinders (α → 60 deg) where separation occurs at the front corners. The inclined cylinder reduces the velocity deficiency in the near-wake, and the reduction in far-wake is the most notable for the α = 30 deg cylinder. The transverse distributions of several quantities are shifted toward the negative y-direction, such as the maximum velocity deficiency and maximum/minimum velocity fluctuation. Finally, the global stability and sensitivity analysis show that the spatial structures of perturbed velocities are quite similar for α ≤ 30 deg and the temporal growth rate of perturbation is sensitive to the near-wake flow, while for α ≥ 40 deg there are remarkable transverse expansion and streamwise elongation of the perturbed velocities, and the growth rate is sensitive to the far-wake flow.

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References

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Figures

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Fig. 1

Schematic of the physical model

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Fig. 3

Time histories of the lift and drag coefficients

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Fig. 4

Instantaneous streamline and vorticity (ωd/U0) fields at α = 0 deg

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Fig. 5

Instantaneous streamline and vorticity (ωd/U0) fields at α = 20 deg

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Fig. 6

Instantaneous streamline and vorticity (ωd/U0) fields at α = 40 deg

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Fig. 7

Instantaneous streamline and vorticity (ωd/U0) fields at α = 60 deg

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Fig. 8

Azimuthal distribution of time-averaged (Cp,avg) and maximum fluctuating (ΔCp) pressure coefficient along the cylinder surface

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Fig. 9

Streamwise distribution of time-averaged velocities along the wake centerline

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Fig. 10

Transverse distribution of time-averaged streamwise velocity (uavg − U0)/U0 at several streamwise stations

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Fig. 11

Streamwise distribution of maximum fluctuating velocities along the wake centerline

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Fig. 12

Transverse distribution of maximum fluctuating streamwise velocity Δu/U0 at several streamwise stations

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Fig. 2

Multiblock grid for the α = 10 deg configuration plotted at every eighth gridline in each direction for clarity

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Fig. 13

Contour of the eigenfunction: (a1)–(g1)  Re(û) and (a2)–(g2)  Re(v̂). The subfigures are plotted at α = 0 deg (10 deg) 60 deg from top to bottom. The dashed line denotes the wake centerline.

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Fig. 14

Growth rate sensitivity to the base flow modification ∇Uσ of the unstable mode: (a)–(g) α = 0 deg (10 deg) 60 deg. The magnitude of ∇Uσ is visualized by the contour and its orientation by arrows.

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