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Research Papers: Multiphase Flows

The Influence of Retraction on Three-Stream Injector Pulsatile Atomization for Air–Water Systems

[+] Author and Article Information
Wayne Strasser

Fellow ASME
Eastman Chemical Company,
Kingsport, TN 37660
e-mail: strasser@eastman.com

Francine Battaglia

Fellow ASME
Department of Mechanical Engineering,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061
e-mail: fbattaglia@vt.edu

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 3, 2015; final manuscript received April 5, 2016; published online July 15, 2016. Assoc. Editor: Samuel Paolucci.

J. Fluids Eng 138(11), 111302 (Jul 15, 2016) (12 pages) Paper No: FE-15-1531; doi: 10.1115/1.4033421 History: Received August 03, 2015; Revised April 05, 2016

Although coaxial airblast primary atomization has been studied for decades, relatively little attention has been given to three-stream designs; this is especially true for transonic self-pulsating injectors. Herein, the effects of nozzle geometry, grid resolution, modulation, and gas flow rate on the acoustics and spray character within an industrial scale system were investigated computationally using axisymmetric (AS) and three-dimensional (3D) models. Metrics included stream pressure pulsations, spray lift-off, spray angle, and primary droplet length scale, along with the spectral alignment among these parameters. Strong interactions existed between geometry and inner gas (IG) feed rate. Additionally, inner nozzle retraction and outer stream meeting angle were intimately coupled. Particular attention was given to develop correlations for various metrics versus retraction; one such example is that injector flow capacity was found to be linearly proportional to retraction. Higher IG flows were found to widen sprays, bringing the spray in closer to the nozzle face, and reducing droplet length scales. Substantial forced modulation of the IG at its dominant tone did not strongly affect many metrics. Incompressible 3D results were similar to some of the AS results, which affirmed the predictive power by running AS simulations as surrogates. Lastly, normalized droplet size versus normalized distance from the injector followed a strikingly similar trend as that found from prior two-fluid air-slurry calibration work.

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References

Figures

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Fig. 1

Time-averaged spray profiles at low IG flow showing effects of geometry from AS simulations

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Fig. 4

Instantaneous contours (case D2) of liquid volume fraction with superimposed velocity vectors showing constructive sinuous and varicose type instabilities between the IG and OG for the flushed design at low IG flow. The right picture is extracted from a randomly chosen later time.

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Fig. 2

Graphical depiction of Table 8, Equation (a) showing the effect of retraction on IG pressure drop for low IG flow AS simulations (Cases A20, D2, and F2)

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Fig. 3

Instantaneous contours (case F2) of liquid volume fraction (left) and pressure (right) showing liquid bridge for fully retracted design from AS simulation at low IG flow. The lower picture is extracted from a later time.

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Fig. 5

Instantaneous contours (case F2) of liquid volume fraction with superimposed velocity vectors showing destructive instability between the IG and OG for the fully retracted design at low IG flow. The right picture is extracted from a randomly chosen later time.

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Fig. 6

Time-averaged spray profiles from AS simulations showing effects of IG flow for base geometry 1

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Fig. 7

Time-averaged spray profiles from AS simulations showing effects of IG flow for flushed geometry 2

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Fig. 8

Instantaneous snapshots of uncorrelated 3D spray surfaces (Case C17) colored by Mach number (M = 0 is blue, M ≥ 0.3 is red) showing various stages of the primary atomization cycle. Black arrows point to relatively high Mach number regions, and purple dashed arrows identify the dramatic change in inner liquid layer radius

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Fig. 9

Axial droplet length scale profiles for 3D simulations

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