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TECHNICAL BRIEFS

Flow Geometry Effects on the Turbulent Mixing Efficiency

[+] Author and Article Information
Roberto C. Aguirre

Iracletos Flow Dynamics and Turbulence Laboratories, Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697raguirre@uci.edu

Jennifer C. Nathman

Iracletos Flow Dynamics and Turbulence Laboratories, Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697jnathman@uci.edu

Haris C. Catrakis1

Iracletos Flow Dynamics and Turbulence Laboratories, Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697catrakis@uci.edu

1

Corresponding author.

J. Fluids Eng 128(4), 874-879 (Feb 09, 2006) (6 pages) doi:10.1115/1.2201696 History: Received September 16, 2004; Revised February 09, 2006

Flow geometry effects are examined on the turbulent mixing efficiency quantified as the mixture fraction. Two different flow geometries are compared at similar Reynolds numbers, Schmidt numbers, and growth rates, with fully developed turbulence conditions. The two geometries are the round jet and the single-stream planar shear layer. At the flow conditions examined, the jet exhibits an ensemble-averaged mixing efficiency which is approximately double the value for the shear layer. This substantial difference is explained fluid mechanically in terms of the distinct large-scale entrainment and mixing-initiation environments and is therefore directly due to flow geometry effects.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematics of the two flow geometries examined and compared presently: the single-stream planar shear layer (top) and the round jet (bottom)

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Figure 2

Top: Example of an experimental high-resolution quantitative visualization of the spatial concentration field generated by a single-stream planar shear layer, showing a streamwise slice. While both the near field and far field are shown in this visualization, the image data utilized to evaluate the mixing efficiency are from the far field. Bottom: Example of an experimental high-resolution quantitative visualization of the space-time concentration far field of a round jet, with time increasing from left to right and the vertical dimension corresponding to transverse distance through the jet and containing the flow centerline.

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Figure 3

Visualizations of the mixed-fluid interfaces and high-gradient regions for the shear layer (top) in a streamwise slice, and for the jet (bottom) in a transverse slice. The grey levels correspond to the magnitude of the in-plane components of the concentration-field gradient for each flow geometry, with darker regions denoting higher-gradient locally thinner interfaces.

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Figure 4

Examples of the regions of mixed fluid (black) in the single-stream shear layer (top) and in the jet (bottom). The boundaries of the mixed-fluid regions correspond to the outer interfaces separating mixed fluid shown in black from the pure fluid(s) shown in white.

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