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SPECIAL SECTION ON THE FLUID MECHANICS AND RHEOLOGY OF NONLINEAR MATERIALS AT THE MACRO, MICRO AND NANO SCALE

Experimental Study on the Helical Flow in a Concentric Annulus With Rotating Inner Cylinder

[+] Author and Article Information
Nam-Sub Woo

School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Koreanswoo@skku.edu

Young-Ju Kim

School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Koreakyjp7272@kigam.re.kr

Young-Kyu Hwang

School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Koreaykhwang@skku.edu

J. Fluids Eng 128(1), 113-117 (Sep 22, 2005) (5 pages) doi:10.1115/1.2136923 History: Received July 20, 2004; Revised September 22, 2005

This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed laminar flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose, respectively, when the inner cylinder rotates at the speed of 0600rpm. The results of the present study show the effect of the bulk flow Reynolds number Re and Rossby number Ro on the skin friction coefficients. They also point to the existence of a flow instability mechanism. The effect of rotation on the skin friction coefficient depends significantly on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change in skin friction coefficient, which corresponds to a variation of the rotational speed, is large for the laminar flow regime, whereas it becomes smaller as Re increases for transitional flow regime and, then, it gradually approaches to zero for turbulent flow regime. Consequently, the critical bulk flow Reynolds number Rec decreases as the rotational speed increases. The rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of experimental apparatus (all dimensions in meters)

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Figure 2

Pressure differences of water as a function of z with various Re

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Figure 3

(a) Pressure losses and (b) skin friction coefficients of water as a function of Re at 0–600rpm

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Figure 4

(a) Pressure losses and (b) skin friction coefficients of 0.4% CMC solution as a function of Re at 0–600rpm

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Figure 5

Pressure losses of 0.4% CMC solution as a function of Re at 200–600rpm

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Figure 6

Normalized relative skin friction coefficients Cf* of water and 0.4% CMC solution as a function of Re at 100–600rpm: (a) water and (b) 0.4% CMC solution

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Figure 7

Relation of Cf Re with Ro for laminar flow in water

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Figure 8

Relation of Cf Re with Ro for laminar flow in 0.4% CMC solution

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