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Research Papers: Flows in Complex Systems

Control of Vortex Shedding Using a Screen Attached on the Separation Point of a Circular Cylinder and Its Effect on Drag

[+] Author and Article Information
Gokturk Memduh Ozkan

Department of Mechanical Engineering,
Çukurova University,
Adana 01330, Turkey
e-mail: gmozkan@cu.edu.tr

Erhan Firat

Department of Mechanical Engineering,
Munzur University,
Tunceli 62000, Turkey
e-mail: efirat@munzur.edu.tr

Huseyin Akilli

Department of Mechanical Engineering,
Çukurova University,
Adana 01330, Turkey
e-mail: hakilli@cu.edu.tr

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 19, 2016; final manuscript received January 19, 2017; published online April 28, 2017. Assoc. Editor: Elias Balaras.

J. Fluids Eng 139(7), 071107 (Apr 28, 2017) (11 pages) Paper No: FE-16-1529; doi: 10.1115/1.4036186 History: Received August 19, 2016; Revised January 19, 2017

The control of flow in the wake of a circular cylinder by an attached permeable plate having various porosity ratios was analyzed experimentally using both particle image velocimetry (PIV) and dye visualization techniques. The force measurements were also done in order to interpret the effect of control method on drag coefficient. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as D = 50 mm and L/D = 1.0, respectively. The porosity ratio, β, which can be defined as the ratio of open surface area to the whole body surface area, was taken as β = 0.4, 0.5, 0.6, 0.7, and 0.8 (permeable plates). The study was performed considering deep water flow conditions with a constant Reynolds number of ReD = 5000 based on the cylinder diameter. Each permeable plate was attached on the separation point and the results were compared with the results of cylinder without permeable plate (plain cylinder) in order to understand the control effect. Both qualitative and quantitative results revealed that the permeable plates of 0.4 ≤ β ≤ 0.6 are effective on controlling the unsteady flow structure downstream of the cylinder, i.e., the vortex formation length was increased, turbulent statistics was reduced and vortex shedding frequency was diminished when the permeable plate attached normal to the cylinder surface from the lower separation point. However, the drag force acting on the cylinder was found to be increased due to the increased cross-sectional area.

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References

Figures

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Fig. 1

Schematic presentation of the control technique and the definition of porosity, β of permeable plate

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Fig. 2

(a) Plan view of the measurement system and (b) side view of the experimental setup

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Fig. 3

A sketch of the wind tunnel test section with force measurement system. Flow is from left to right.

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Fig. 4

Dye visualization pictures for plain cylinder and all controlled cases

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Fig. 5

Time-averaged Reynolds shear stress concentrations, <u′v′>, vorticity contours, <ω*> and streamline topologies, <ψ> for all cases, as well as the plain cylinder. In plots, |<ω*>|min = |<ω*>| = 2.1 and |<u′v′>| = 0.01.

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Fig. 6

Change in effective shear layer lengths for upper and lower shear layers with respect to porosity, β

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Fig. 7

The spatial distribution of turbulent kinetic energy <TKE>, streamwise Reynolds normal stress <u′u″>, spanwise Reynolds normal stress <v′v′> for all cases, as well as the plain cylinder. In plots, |<TKE>|min = |<TKE>| = 0.02, |<u′u′>|min = |<u′u′>| = 0.02 and |<v′v′>|min = |<v′v′>| = 0.01.

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Fig. 8

Peak magnitudes of time-averaged turbulent kinetic energy, <TKE>max with respect to porosity, β

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Fig. 9

Spectra of streamwise velocity fluctuations for the plain cylinder at streamwise location of x/d = 1.6 and spanwise location of y/d = 2

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Fig. 10

(a) Spectra of streamwise velocity component, SU for β = 0.7 at various downstream locations and (b) spectra of streamwise velocity component, SU for β = 0.8 at various downstream locations

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Fig. 11

The effect of porosity on drag coefficient of the cylinder, <CD> based on cylinder diameter and total cross section

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