The influence of gas phase velocity fluctuations on primary atomization and droplet deformation

The influence of gas phase velocity fluctuations on primary atomization and droplet deformation The effects of grid-generated velocity fluctuations on the primary atomization and subsequent droplet deformation of a range of laminar liquid jets are examined using microscopic high-speed backlit imaging of the break-up zone and laser Doppler anemometry of the gas phase separately. This is done for fixed gas mean flow conditions in a miniature wind tunnel experiment utilizing a selection of fuels, turbulence-generating grids and two syringe sizes. The constant mean flow allows for an isolated study of velocity fluctuation effects on primary atomization in a close approximation to homogeneous decaying turbulence. The qualitative morphology of the primary break-up region is examined over a range of turbulence intensities, and spectral analysis is performed in order to ascertain the break-up frequency which, for a case of no grid, compares well with the existing literature. The addition of velocity fluctuations tends to randomize the break-up process. Slightly downstream of the break-up region, image processing is conducted in order to extract a number of metrics, which do not depend on droplet sphericity, and these include droplet aspect ratio and orientation, the latter quantity being somewhat unconventional in spray characterization. A turbulent Weber number $$We^{\prime}$$ W e ′ which takes into account gas phase fluctuations is utilized to characterize the resulting droplet shapes, in addition to a mean Weber number <We d>. Above a $$We^{\prime}>0.05$$ W e ′ > 0.05 a clear positive relationship exists between the mean aspect ratio of droplets and the turbulent Weber number where $$We^{\prime}$$ W e ′ is varied by altering all relevant variables including the velocity root mean square, the initial droplet diameter, the surface tension and the density. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

The influence of gas phase velocity fluctuations on primary atomization and droplet deformation

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Publisher
Springer Berlin Heidelberg
Copyright
Copyright © 2014 by Springer-Verlag Berlin Heidelberg
Subject
Engineering; Engineering Fluid Dynamics; Fluid- and Aerodynamics; Engineering Thermodynamics, Heat and Mass Transfer
ISSN
0723-4864
eISSN
1432-1114
D.O.I.
10.1007/s00348-013-1659-3
Publisher site
See Article on Publisher Site

Abstract

The effects of grid-generated velocity fluctuations on the primary atomization and subsequent droplet deformation of a range of laminar liquid jets are examined using microscopic high-speed backlit imaging of the break-up zone and laser Doppler anemometry of the gas phase separately. This is done for fixed gas mean flow conditions in a miniature wind tunnel experiment utilizing a selection of fuels, turbulence-generating grids and two syringe sizes. The constant mean flow allows for an isolated study of velocity fluctuation effects on primary atomization in a close approximation to homogeneous decaying turbulence. The qualitative morphology of the primary break-up region is examined over a range of turbulence intensities, and spectral analysis is performed in order to ascertain the break-up frequency which, for a case of no grid, compares well with the existing literature. The addition of velocity fluctuations tends to randomize the break-up process. Slightly downstream of the break-up region, image processing is conducted in order to extract a number of metrics, which do not depend on droplet sphericity, and these include droplet aspect ratio and orientation, the latter quantity being somewhat unconventional in spray characterization. A turbulent Weber number $$We^{\prime}$$ W e ′ which takes into account gas phase fluctuations is utilized to characterize the resulting droplet shapes, in addition to a mean Weber number <We d>. Above a $$We^{\prime}>0.05$$ W e ′ > 0.05 a clear positive relationship exists between the mean aspect ratio of droplets and the turbulent Weber number where $$We^{\prime}$$ W e ′ is varied by altering all relevant variables including the velocity root mean square, the initial droplet diameter, the surface tension and the density.

Journal

Experiments in FluidsSpringer Journals

Published: Jan 16, 2014

References

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