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Research Papers: Jets, Wakes, and Impingment Cooling

Influence of a Coflowing Ambient Stream on a Turbulent Axisymmetric Buoyant Jet

[+] Author and Article Information
S. Habli

 Unité de thermique et environnement, Ecole Nationale d’Ingénieurs de Monastir, route de Ouardanine, 5020 Monastir, Tunisiesabra.habli@fsm.rnu.tn

N. Mahjoub Said, H. Mahmoud, H. Mhiri

 Unité de thermique et environnement, Ecole Nationale d’Ingénieurs de Monastir, route de Ouardanine, 5020 Monastir, Tunisie

G. Le Palec, Ph. Bournot

Equipe IMFT, Institut de Mécanique de Marseille, UNIMECA, 60 rue Joliot-Curie, Technopôle de Château-Gombert, 13453 Marseille Cedex 13, France

J. Heat Transfer 130(2), 022201 (Feb 04, 2008) (15 pages) doi:10.1115/1.2804930 History: Received May 25, 2006; Revised June 01, 2007; Published February 04, 2008

This paper reports numerical results on turbulent buoyant axisymmetric jets in a coflowing ambient stream. The objective of this study is to compare the performance of the Reynolds stress algebraic model (ASM) with that of the k-ε turbulence model in predicting the flow field. A finite difference method has been used to solve a system of coupled partial differential equations. A comparison has been carried out between the numerical results obtained in the present work and experimental and numerical data reported in the literature. It has been found that the two investigated models reasonably predict the mean flow properties of the flow field. Nevertheless, the ASM proves to be better than the k-ε method to predict the effects of buoyancy and the turbulence structure. It has been found that the increase of the coflow can slow the development of the jet to the state of similarity of mean characteristic profiles. A jet with a ratio of coflow velocity u¯ to jet discharge velocity u¯0 less than 0.05 has developed to closely approximate a free jet in a stagnant medium while a jet with higher u¯u¯0 ratio never reaches a similarity state. In buoyant jets, only a flow with uu00.05 reaches a similarity state. Buoyancy ensures that the similarity region begins at a distance closer to the nozzle exit than if the medium is stagnant.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Effect of the grid on the centerline longitudinal distribution of velocity: uco=0.01. (a) Effect of the axial step on the flow:Δr=0.025d. (b) Effect of the radial step on the flow: (Δx1=0.001d for x>5d) and (Δx2=0.01d for x⩾5d).

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Figure 2

Longitudinal distributions of the centerline excess velocity

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Figure 3

Potential core for different initial intensity of the turbulent kinetic energy: uco=0.01

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Figure 4

Radial distributions of the longitudinal excess velocity

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Figure 5

Longitudinal distributions of centerline excess temperature

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Figure 6

Radial distributions of the longitudinal excess temperature

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Figure 7

Radial distributions of the Reynolds shear stress

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Figure 8

Radial distributions of the heat flux

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Figure 9

Centerline distributions of numerical solutions for a buoyant jet: uco=0.01

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Figure 10

Axial distributions of the centerline longitudinal velocity for different velocity coflows

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Figure 11

Radial distributions of the excess velocity at several downstream stations and for different coflowing streams

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Figure 12

Axial distributions of the dynamic half-radius of the jet for different coflows

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Figure 13

Axial distributions of the turbulence kinetic energy for (a) different coflows and (b) different levels of k0∕u¯02:uco=0.01

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Figure 14

Radial distributions of the budget for the turbulent kinetic energy transport equation at several downstream stations: uco=0.01

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Figure 15

Radial distributions of the budget for the turbulent kinetic energy transport equation for different coflowing streams: x∕d=20

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Figure 16

Longitudinal distributions for different Froude numbers of (a) the centerline excess velocity and (b) the dynamic half-radius: uco=0.174

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Figure 17

Longitudinal distributions for different Froude numbers of (a) the centerline excess temperature and (b) the thermal half-radius: uco=0.174

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Figure 18

Longitudinal distributions of the turbulent kinetic energy for different Froude numbers: uco=0.174

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Figure 19

Centerline longitudinal distributions of the velocity for different coflowing streams: Fr=20

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Figure 20

Radial distributions of the excess velocity at several downstream stations and for different coflowing streams: Fr=20

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Figure 21

Longitudinal distributions for different co-flowing streams of (a) the centerline excess temperature and (b) the thermal half-radius: Fr=20

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Figure 22

Longitudinal distributions of the centerline turbulent kinetic energy for different coflowing streams: Fr=20

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