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Research Papers: CFD and VIV

Numerical Simulations of an Oscillating Flow Past an Elliptic Cylinder

[+] Author and Article Information
Sid'Ahmed Daoud

Department of Mechanical,
Mostaganem University UMAB,
BP 300, Route Belhacel,
Mostaganem 27000, Algeria
e-mail: daoudsidahmed@yahoo.fr

Driss Nehari

Smart Structures Laboratory,
University Center of Ain Temouchent,
BP 284,
Ain Temouchent 46000, Algeria
e-mail: nehari_dr@yahoo.fr

Mohamed Aichouni

Industrial Engineering Department,
University of Hail,
P.O. Box 2440,
Hail 81441, Saudi Arabia
e-mail: m_aichouni@yahoo.co.uk

Taieb Nehari

Smart Structures Laboratory,
University Center of Ain Temouchent,
BP 284,
Ain Temouchent 46000, Algeria
e-mail: nehari_tb@yahoo.fr

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 13, 2013; final manuscript received October 23, 2015; published online November 25, 2015. Editor: Solomon Yim.

J. Offshore Mech. Arct. Eng 138(1), 011802 (Nov 25, 2015) (11 pages) Paper No: OMAE-13-1034; doi: 10.1115/1.4031926 History: Received April 13, 2013; Revised October 23, 2015

This paper presents a numerical investigation of a two-dimensional (2D) oscillatory flow around a cylinder of different elliptic ratios, in order to study the effect of the elliptic form of the cylinder on the vorticity field and the hydrodynamic forces that act on it. The elliptic ratio ε was varied from 1 to 0.1, where the small axis is parallel to the flow direction, simulating cases ranging from a circular cylinder to the case of a cylinder with a profiled elliptic section. The investigations presented here are for Reynolds number Re = 100 and Keulegan number KC = 5. The numerical visualization of the flow for different elliptic ratios shows five different modes of vortex shedding (symmetric and asymmetric pairing of attached vortices, single-pair, double-pair, and chaotic), which depend on the range of the elliptic ratio. The results show that the longitudinal force increases with the reduction of the elliptic ratio. The transverse force appears from the elliptic ratio ε=0.75 and increases with the reduction of this ratio in the range of 0.75ε0.4, then decreases for ε<0.4. On the other hand, concerning the Morison coefficients the results show that the drag coefficient is sensitive to the swirling layout while the coefficient of inertia does not seem to be much affected by the geometry of the cylinder.

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References

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Figures

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Fig. 1

Cartography identifying various flow modes in plan KC − β [9]. A*: symmetrical and attached, 2D; A: symmetrical with swirling layout; B: longitudinal swirls 3D; C: rearrangement of large swirls, 3D; D: gone transverse; E: transverse alley with irregular commutation 3D; F: diagonal double pair, 3D; and G: transverse vortex.

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Fig. 2

Schematic diagram of the flow configuration investigated

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Fig. 3

Typical H-grid used in the computations. The grid is for the (x, z)-plane.

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Fig. 4

Grid independence tests for the nondimensional total inline force: (a) ε=0.7 during the 60th cycle and (b) ε=0.3 during the 35th cycle

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Fig. 5

Evolution of the vorticity field for the elliptic ratio  ε=0.8  

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Fig. 6

Evolution of the pressure field for the elliptic ratio ε=0.8  

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Fig. 7

Various positions of the vortex shedding for ε=0.65: (a) vortex shedding in the z>0 side and (b) vortex shedding in the z<0 side

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Fig. 8

Evolution of the vorticity field during the 35th cycle for the elliptic ratio ε=0.6

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Fig. 9

Evolution of the pressure field during the 35th cycle for the elliptic ratio ε=0.6

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Fig. 10

Evolution of the vorticity field during the 65th cycle for the elliptic ratio ε=0.4

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Fig. 11

Evolution of the pressure field during the 65th cycle for the elliptic ratio ε=0.4

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Fig. 12

Comparison between swirling losses for various elliptic ratios

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Fig. 13

History of vorticity forms during 200 cycles for  ε=0.6 , 0.5, and 0.4, where represents a cycle developing pairs of contra rotating swirls and represents an intermittent cycle: (a) ε=0.6, (b)  ε=0.5, and (c) ε=0.4

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Fig. 14

Evolution of the vorticity field for the elliptic ratio ε=0.35

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Fig. 15

Comparison between swirling losses of double-pair mode for ε=0.3 and 0.1 : (a) ε=0.3 during the 55th cycle and (b) ε=0.1 during the 130th cycle

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Fig. 16

Comparison between swirling losses of single-pair mode for ε=0.3 and 0.1: (a)  ε=0.3 during the 155th cycle and (b) ε=0.1 during the 174th cycle

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Fig. 17

History of vorticity forms during 200 cycles for ε=0.3,0.25, and 0.1, where represents a single-pair mode cycle, double-pair mode cycle, and represents an intermittent cycle developing complex swirling detachments: (a) ε=0.3, (b) ε=0.25, and (c) ε=0.1

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Fig. 18

History of the nondimensional total transverse force in regime A for various elliptic ratios

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Fig. 19

History of the nondimensional total longitudinal force in regime A for various elliptic ratios

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Fig. 20

Time evolution of the (a) pressure force and (b) shear force during the 90th cycle for various elliptic ratios: (a) longitudinal pressure force (Fx,p) and (b) longitudinal shear force (Fx,s)

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Fig. 21

Effect of the elliptic ratio on the standard deviation of the longitudinal and transverse forces

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Fig. 22

Effect of the elliptic ratio on the coefficients of Morison

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