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Research Papers: Fundamental Issues and Canonical Flows

A Comparison Between the Separated Flow Structures Near the Wake of a Bare and a Foam-Covered Circular Cylinder

[+] Author and Article Information
Iman Ashtiani Abdi

Mem. ASME
QGECE,
School of Mechanical and
Mining Engineering,
The University of Queensland,
Queensland 4072, Australia
e-mail: i.ashtiani@uq.edu.au

Kamel Hooman

QGECE,
School of Mechanical and
Mining Engineering,
The University of Queensland,
Queensland 4072, Australia
e-mail: k.hooman@uq.edu.au

Morteza Khashehchi

QGECE,
School of Mechanical and
Mining Engineering,
The University of Queensland,
Queensland 4072, Australia
e-mail: m.khashehchi@uq.edu.au

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 7, 2013; final manuscript received May 10, 2014; published online September 10, 2014. Assoc. Editor: Peter Vorobieff.

J. Fluids Eng 136(12), 121203 (Sep 10, 2014) (8 pages) Paper No: FE-13-1595; doi: 10.1115/1.4027686 History: Received October 07, 2013; Revised May 10, 2014

The flow structures behind bare and aluminum foam-covered single circular cylinders were investigated using particle image velocimetry (PIV). The experiments are conducted for a range of Reynolds numbers from 2000 to 8000, based on the outer cylinders diameter and the air velocity upstream of the cylinder. The analysis of the PIV data shows the important effects of the foam cover and the inlet velocity on the separated structures. The results show a considerable increase in the wake size behind a foam-covered cylinder compared to that of a bare cylinder. Furthermore, the turbulence intensity is found to be around 10% higher in the case of the foam-covered cylinder where the wake size is approximately doubled for the former case compared to the latter. The turbulence kinetic energy, however, is found to be less Reynolds dependent in the case of the foam-covered cylinder. In addition, small scale structures contribute to the formation of the flow structures in the foam-covered cylinder making them a more efficient turbulent generator for the next rows when used in a heat exchanger tube bundle. On the other hand, a higher energy level in such separated structures will translate into increased pressure drop compared to bare cylinders. Finally, the results of this study can be used as an accurate set of boundary conditions for modeling the flow field past such cylinders.

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Figures

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Fig. 1

Wind tunnel schematic

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Fig. 2

Schematic of the experimental setup. The laser is located above the field of view on top of the wind tunnel. Two adjacent cameras face the laser light sheet. Cross represents the coordination center.

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Fig. 3

Bare and foam-covered cylinder samples

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Fig. 4

Normalized average traverse velocity 6D away from the bare cylinder

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Fig. 5

Normalized average streamwise velocity along the center of the cylinder's span along the field of view center line (Y/D = 0)

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Fig. 6

Streamlines for the flow over bare cylinder at Re = 2000 and 8000

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Fig. 7

Streamlines for the flow over foam-covered cylinder at Re = 2000 and 8000

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Fig. 8

Dimensional turbulence kinetic energy along the FOV center line (Y/D = 0)

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Fig. 9

Traverse comparison of normalized turbulence kinetic energy for different Re values at 2D downstream of cylinders

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Fig. 10

Streamwise comparison of normalized turbulence kinetic energy for different Re values downstream of cylinders along the field of view center line (Y/D = 0)

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Fig. 11

Streamwise comparison of turbulence intensity between different cases along the field of view center line (Y/D = 0)

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Fig. 12

Comparison of POD modes between foam-covered and bare cylinders at different Reynolds numbers

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Fig. 13

Visualization of the four modes for the bare cylinder at Reynolds number 2000

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Fig. 14

Visualization of the four modes for the foam-covered cylinder at Reynolds number 2000

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