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Research Papers: Fundamental Issues and Canonical Flows

Characteristics of the Wake Behind a Transversely Oscillating Cylinder Near a Wall

[+] Author and Article Information
S. Peter

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati, Assam 781039, India

A. K. De

Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati, Assam 781039, India
e-mail: akd@iitg.ernet.in

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 15, 2016; final manuscript received October 6, 2016; published online January 19, 2017. Assoc. Editor: Praveen Ramaprabhu.

J. Fluids Eng 139(3), 031201 (Jan 19, 2017) (8 pages) Paper No: FE-16-1098; doi: 10.1115/1.4035012 History: Received February 15, 2016; Revised October 06, 2016

In the present study, numerical investigation is carried out for flow past a transversely oscillating circular cylinder near a wall. A second-order finite-volume method employing diffuse interface immersed boundary method is used to handle the nonconforming boundaries. The cylinder is allowed to oscillate on a fixed Eulerian mesh in order to handle the moving boundary. Simulations are carried out for a number of forcing frequencies at three different gap distances and two amplitudes of oscillation with Reynolds number fixed at 200. While a pair of vortices is found to be shed near the stationary shedding frequency at larger gap distance, multiple interconnected vortices are observed at larger forcing frequencies. Proximity of the wall promotes greater interaction of the wall layer with the near wake resulting in inhibited irregular shedding. Energy transfer changes its direction when the correlation between the cylinder motion and the lift force is strongest. Positive energy transfer attains a peak at the onset of the synchronization regime accompanied by a weaker correlation. Amplitude of oscillation of the cylinder evidently has systematic effect on the drag coefficient and wake fluctuations, though lift force remains grossly unaltered. Lower amplitude of motion favors induced motion as opposed to larger ones where greater negative energy transfer occurs.

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Figures

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Fig. 1

Schematic diagram of the flow geometry and boundary conditions

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Fig. 2

Comparisons of CD and CL signals for transversely oscillating cylinder in freestream

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Fig. 3

Time traces of CD and CL at different grid levels and domain sizes

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Fig. 4

A blown-up view of the computing grid (M5) where every second grid line is shown

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Fig. 5

Instantaneous vorticity field at extreme frequency ratios for A = 0.2

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Fig. 6

Six instantaneous snapshots within one cycle of cylinder motion for g/d=0.5,fr=1.5, and A=0.2. The time instances are marked on the CL curve (solid line) plotted with the cylinder motion (dashed line) in the inset.

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Fig. 7

Six instantaneous snapshots within one cycle of cylinder oscillation for g/d=2,fr=0.9, and A=0.2 as plotted in Fig.6

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Fig. 8

Instantaneous vorticity field at extreme frequency ratios for A = 0.4

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Fig. 9

Six instantaneous snapshots within one cycle of cylinder motion for g/d=2,fr=1.5, and A=0.4 as plotted in Fig. 6

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Fig. 10

Frequency spectra of the lift signal; two left columns a/d=0.2 and two right columns a/d=0.4

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Fig. 11

Normalized vortex shedding frequency fs by the natural shedding frequency fo as a function of the frequency ratio fr

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Fig. 12

Time histories of CD and CL for fr=0.8 (odd rows) and 1.5 (even rows) at g/d=0.5 (first two rows), 1 (third and fourth rows), and 2 (last two rows) with a/d=0.2 (left column) and 0.4 (right column)

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Fig. 13

Time histories of energy rate at three frequency ratios for a/d=0.2 (top two rows) and 0.4 (bottom two rows) with g/d=0.5 (odd rows) and 2 (even rows)

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Fig. 14

Variation of correlation coefficient between the lift force (CL) and cylinder motion (ys) (left) and energy coefficient (CE) (right) with frequency ratio

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Fig. 15

Average and RMS of drag 〈CD〉,CD′ and lift 〈CL〉,CL′ coefficients as a function of frequency ratio

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