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Research Papers: Forced Convection

Turbulent Forced Convection in a Plane Asymmetric Diffuser: Effect of Diffuser Angle

[+] Author and Article Information
H. Lan, B. F. Armaly, J. A. Drallmeier

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, MO 65401

J. Heat Transfer 131(7), 071702 (May 13, 2009) (8 pages) doi:10.1115/1.2977545 History: Received January 02, 2008; Revised April 25, 2008; Published May 13, 2009

A simulation of two-dimensional turbulent forced convection in a plane asymmetric diffuser with an expansion ratio of 4.7 is performed, and the effect of the diffuser angle on the flow and heat transfer is reported. This geometry is common in many heat exchanging devices, and the turbulent convective heat transfer in it has not been examined. The momentum transport in this geometry, however, has received significant attention already, and the studies show that the results from the υ2¯f type turbulence models provide better agreement with measured velocity distributions than that from the kε or kω turbulence models. In addition, the υ2¯f type turbulence models have been shown to provide good heat transfer results for separated and reattached flows. The kεζ (υ2¯f type) turbulence model is used in this study due to its improved numerical robustness, and the FLUENT-CFD code is used as the simulation platform. User defined functions for the kεζ turbulence model were developed and incorporated into the FLUENT-CFD code, and that process is validated by simulating the flow and the heat transfer in typical benchmark problems and comparing these results with available measurements. This new capability is used to study the effect of the diffuser angle on forced convection in an asymmetric diffuser, and the results show that the angle influences significantly both the flow and the thermal field. The increase in that angle increases the size of the recirculation flow region and enhances the rate of the heat transfer.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Fully developed velocity distribution in the channel flow at Reτ=590

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Figure 2

Turbulence scalar distribution in the channel flow at Reτ=590

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Figure 3

Mean stream velocity distribution in the recirculation region

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Figure 4

Stanton number comparison for the heated wall in the backward-facing step flow

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Figure 5

Nusselt number comparison for the normally impinged jet flow on a flat plate

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Figure 6

Mean stream velocity comparison in a 10deg diffuser

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Figure 7

Skin friction coefficient comparison for a 10deg diffuser

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Figure 8

Schematic of the asymmetric diffuser and the computational domain

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Figure 9

Body-fitted grid for diffuser angles smaller than (including) 30deg

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Figure 10

Quasiquadrilateral grid for diffuser angles greater than (including) 60deg

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Figure 11

Streamlines in diffusers with different diffusers

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Figure 12

Temperature contours in diffusers with different diffusers

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Figure 13

Temperature along the heated wall in different diffusers

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Figure 14

Streamwise distribution of bulk temperature in different diffusers

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Figure 15

Stanton number distribution along the heated wall in different diffusers

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