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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Nonlinear Breakup Model for a Liquid Sheet Emanating From a Pressure-Swirl Atomizer

[+] Author and Article Information
Ashraf A. Ibrahim

Department of Mechanical, Industrial, and Nuclear Engineering, 598 Rhodes Hall, P.O. Box 210072, University of Cincinnati, Cincinnati, OH 45221

Milind A. Jog1

Department of Mechanical, Industrial, and Nuclear Engineering, 598 Rhodes Hall, P.O. Box 210072, University of Cincinnati, Cincinnati, OH 45221Milind.Jog@uc.edu

1

Corresponding author.

J. Eng. Gas Turbines Power 129(4), 945-953 (Jan 30, 2007) (9 pages) doi:10.1115/1.2747263 History: Received August 16, 2006; Revised January 30, 2007

Predictions of breakup length of a liquid sheet emanating from a pressure-swirl (simplex) fuel atomizer have been carried out by computationally modeling the two-phase flow in the atomizer coupled with a nonlinear analysis of instability of the liquid sheet. The volume-of-fluid (VOF) method has been employed to study the flow field inside the pressure-swirl atomizer. A nonlinear instability model has been developed using a perturbation expansion technique with the initial amplitude of the disturbance as the perturbation parameter to determine the sheet instability and breakup. The results for sheet thickness and velocities from the internal flow solutions are used as input in the nonlinear instability model. Computational results for internal flow are validated by comparing film thickness at exit, spray angle, and discharge coefficient with available experimental data. The predictions of breakup length show a good agreement with semiempirical correlations and available experimental measurements. The effect of elevated ambient pressure on the atomizer internal flow field and sheet breakup is investigated. A decrease in air core diameter is obtained at higher ambient pressure due to increased liquid-air momentum transport. Shorter breakup lengths are obtained at elevated air pressure. The coupled internal flow simulation and sheet instability analysis provides a comprehensive approach to modeling sheet breakup from a pressure-swirl atomizer.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of pressure swirl atomizer

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Figure 2

A schematic of annular liquid sheet

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Figure 3

Velocity vectors in the atomizer (case 1)

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Figure 4

Volume fraction contours (case 4) (a) computational prediction and (b) experimental observation from Ma (34)

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Figure 5

Effect of air pressure on the air core diameter

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Figure 6

Evolution of the dimensionless inner and outer surfaces deformation at the dominant wave number of k=0.16 for WeL=300, Ui=Uo=0, gi=go=0.0012(ηo=0.1) (a) T=0, (b) T=35, and (c) T=54.5

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Figure 7

Comparison of dimensionless breakup length predictions with Kim (37)

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Figure 8

Evolution of the dimensionless inner and outer surfaces deformation at different density ratios for WeL=300, Ui=Uo=0, and ηo=0.01. (a) gi=go=0.0012 and k=0.16; (b) gi=go=0.006 and k=0.95; and (c) gi=go=0.012 and k=2.25.

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