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RESEARCH PAPERS: Forced Convection

Heat Transfer and Fluid Flow Characteristics of Separated Flows Encountered in a Backward-Facing Step Under the Effect of Suction and Blowing

[+] Author and Article Information
E. Abu-Nada

Department of Mechanical Engineering, Hashemite University, Zarqa, 13115, Jordaneiyad@hu.edu.jo

A. Al-Sarkhi, B. Akash, I. Al-Hinti

Department of Mechanical Engineering, Hashemite University, Zarqa, 13115, Jordan

J. Heat Transfer 129(11), 1517-1528 (Feb 01, 2007) (12 pages) doi:10.1115/1.2759973 History: Received August 22, 2006; Revised February 01, 2007

Numerical investigation of heat transfer and fluid flow over a backward-facing step (BFS), under the effect of suction and blowing, is presented. Here, suction/blowing is implemented on the bottom wall (adjacent to the step). The finite volume technique is used. The distribution of the modified coefficient of friction and Nusselt number at the top and bottom walls of the BFS are obtained. On the bottom wall, and inside the primary recirculation bubble, suction increases the modified coefficient of friction and blowing reduces it. However, after the point of reattachment, mass augmentation causes an increase in the modified coefficient of friction and mass reduction causes a decrease in modified coefficient of friction. On the top wall, suction decreases the modified coefficient of friction and blowing increases it. Local Nusselt number on the bottom wall is increased by suction and is decreased by blowing, and the contrary occurs on the top wall. The maximum local Nusselt number on the bottom wall coincides with the point of reattachment. High values of average Nusselt number on the bottom wall are identified at high Reynolds numbers and high suction bleed rates. However, the low values correspond to high blowing rates. The reattachment length and the length of the top secondary recirculation bubble are computed under the effect of suction and blowing. The reattachment length is increased by increasing blowing bleed rate and is decreased by increasing suction bleed rate. The spots of high Nusselt number, and low coefficient of friction, are identified by using contour maps.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the problem geometry and boundary conditions

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Figure 2

(a) Computational mesh and (b) typical control volume

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Figure 3

Model validation: (a) reattachment length versus Reynolds number for various expansion ratios; (b) temperature profiles, Re=800; (c) velocity profiles, x=3 and 7, Re=800; and (d) velocity profiles, x=15 and 30, Re=800

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Figure 4

(a) Reattachment length, (b) beginning of secondary recirculation bubble on the top wall, (c) end of secondary recirculation bubble on the top wall, and (d) length of top-wall recirculation zone

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Figure 5

Distribution of coefficient of friction: (a) Bottom wall Re=400(b) bottom wall Re=800, (c) top wall Re=400, and (d) top wall Re=800

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Figure 6

x component of velocity (u) and velocity gradients profiles(du∕dy) for Re=400: (a)u at x=2.0, (b)du∕dy at x=2.0, (c)u at x=3.0, (d)du∕dy at x=3.0, (e)u at x=5.50, (f)du∕dy at x=5.50, (g)u at x=8.0, and (h)du∕dy at x=8.0

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Figure 7

Streamline patterns for Re=400: (a)σ=0, (b)σ=−0.005, (c)σ=0.005

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Figure 8

Average coefficient of friction versus bleed coefficient

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Figure 9

Contour maps of modified coefficient of friction: (a) Bottom wall and (b) top wall

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Figure 10

Distribution of Nusselt number: (a) Bottom wall Re=400, (b) bottom wall Re=800, (c) top wall Re=400, and (d) top wall Re=800

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Figure 11

Temperature profiles Re=400: (a)x=2.0, (b)x=3.0, (c)x=5.50, and (d)x=8.0

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Figure 12

Temperature isocontours for Re=400: (a)σ=0, (b)σ=−0.005, and (c)σ=0.005

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Figure 13

Average Nusselt number distribution versus bleed coefficient for Re=800 and Re=400

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Figure 14

Contour maps of average Nusselt number: (a) Bottom wall and (b) top wall

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