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Research Papers

Hydrodynamic In-Line Force Coefficients of Oscillating Bluff Cylinders (Circular and Square) at Low Reynolds Numbers

[+] Author and Article Information
A. Barrero-Gil

ETSIA Aeronauticos IDR/UPM Departamento de Motopropulsion y Fluidodinamica, Universidad Politecnica de Madrid, Madrid 28040, Spainantonio.barrero@upm.es

J. Vib. Acoust 133(5), 051012 (Sep 20, 2011) (6 pages) doi:10.1115/1.4003946 History: Received October 06, 2010; Revised February 02, 2011; Published August 31, 2011; Online September 20, 2011

An attempt to measure indirectly the hydrodynamic drag (cD) and inertia (cM) coefficients on oscillating bluff cylinders (circular and square) in quiescent fluid at low Reynolds numbers (low Stokes number) is presented. The Keulegan–Carpenter number was below 15. The experimental approach is based on performing free-decay tests of a spring-mounted cylinder submerged in a water tank. The identification of the instantaneous modal parameters (damping and frequency), via Hilbert transform, of the decaying oscillations allows the determination of (cD) and (cM) by direct comparison with the damping and natural frequency of the system in still air (tank without water). Advantages and shortcomings of this novel experimental approach are presented along the paper.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Oscillating bluff body is a still fluid. Main parameters governing the problem.

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Figure 2

Experimental setup

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Figure 3

Free vibration of the system (circular cylinder mounted) in still air (a). In (b) the temporal evolution of the amplitude, as well as the instantaneous frequency, obtained via Hilbert transform, is shown.

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Figure 4

Linearity of the mechanical damping measured in still air (circular cylinder mounted)

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Figure 5

(a) Decaying oscillations in water (circular cylinder). (b) Drag and inertia coefficients computed via Hilbert transform method. β≈29.

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Figure 6

Mean value and standard deviation of drag (a) and inertia (b) coefficients computed via Hilbert transform method from ten runs, β≈29.

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Figure 7

Identified mean values of drag (a) and inertia (b) by the present method (open circles; β≈29) and measured by Kuhtz (7) (black circles; β=34). Numeric values computed by Iliadis and Agnatopoulos (11) (squares) and Dustz (triangles) (10) are also shown, β=35.

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Figure 8

Identified mean values of drag (a) and inertia (b) by the present method (open circles; β≈40). It is also shown numeric values computed by Zheng and Dalton (13) (black circle) and by Scolan and Faltinsen (14) (open squares); β=213.

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