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TECHNICAL PAPERS

Simulation and Analysis of High-Speed Droplet Spray Dynamics

[+] Author and Article Information
H. Shi

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910

C. Kleinstreuer1

Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910ck@eos.ncsu.edu

1

Corresponding author.

J. Fluids Eng 129(5), 621-633 (Oct 19, 2006) (13 pages) doi:10.1115/1.2717621 History: Received May 28, 2006; Revised October 19, 2006

An experimentally validated computer simulation model has been developed for the analysis of gas-phase and droplet characteristics of isothermal sprays generated by pressure jet atomizers. Employing a coupled Euler-Lagrange approach for the gas-droplet flow, secondary droplet breakup (based on the ETAB model), was assumed to be dominant and the k-ε model was selected for simulating the gas flow. Specifically, transient spray formation in terms of turbulent gas flow as well as droplet velocities and size distributions are provided for different back pressures. Clearly, two-way coupling of the phases is important because of the impact of significant gas entrainment, droplet momentum transfer, and turbulent dispersion. Several spray phenomena are discussed in light of low back-pressure (1atm) and high back-pressure (30atm) environments. At low back-pressure, sprays have long thin geometric features and penetrate faster and deeper than at high back-pressures because of the measurable change in air density and hence drag force. Away from the nozzle exit under relatively high back pressures, there is no distinct droplet size difference between peripheral and core regions because of the high droplet Weber numbers, leading to very small droplets which move randomly. In contrast to transient spray developments, under steady-state conditions droplets are subject to smaller drag forces due to the fully-developed gas entrainment velocities which reduce gas-liquid slip. Turbulent dispersion influences droplet trajectories significantly because of the impact of random gas-phase fluctuations.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Droplet spray generation: (a) spray device as well as primary and secondary breakups; (b) droplet breakup mechanism

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Figure 2

Mesh generation for the computational flow domain

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Figure 3

Computer model validation with experimental spray data

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Figure 4

Spray droplet size and axial velocity patterns for case 1a at different times (i.e., t=0.25ms, 0.5ms, 0.75ms, and 1.0ms)

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Figure 5

Spray droplet size and axial velocity patterns for case 1b at different times (i.e., t=0.5ms, 1.0ms, 1.5ms, and 2.0ms)

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Figure 6

Droplet size distribution for case 1a (transient)

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Figure 7

Droplet size distribution for case 1b (transient)

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Figure 8

Gas entrainment velocity and turbulence kinetic energy distributions for case 1a at different times (i.e., t=0.25ms, 0.5ms, 0.75ms, and 1.0ms)

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Figure 9

Gas entrainment velocity and turbulence kinetic energy distributions for case 1b at different times (i.e., t=0.5ms, 1.0ms, 1.5ms, and 2.0ms)

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Figure 10

Droplet size distribution for case 1a under steady-state condition

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Figure 11

Comparison of droplet axial velocity, gas axial velocity, and droplet volume mean diameter as a function of radial distance between transient simulation and steady-state simulation for case 1a

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