INSTANTANEOUS AND PLANAR
VISUALIZATION OF SUPERSONIC GAS JETS AND SPRAYS T.
K. Kim, S. Y. Son, and K
D. Kihm An
alternative use of Rayleigh- and Mie-scattering techniques
allows separate examination of high-speed air jets and
their airblast atomization characteristics. The molecular
clusters of condensed vapor in sonic or supersonic gas
jets fall in the Rayleigh range (d « |
) and the scattered light from these particles can visualize the development
of high-speed jets and shear mixing with ambient air.
When the tested liquid is injected, the Mie-scattering
signals from the spray droplets, which are in the Mie
range (d = 
or d > 
), enable visualization of the liquid spray development. A comparative study
of gas jets and sprays has been made for both converging
nozzle (SN type) and a converging-diverging nozzle (CD
type). The present visualization study reveals some
explanations for the different atomization characteristics
of the two types of nozzles under identical injection
conditions.Visualization of high-speed
gas jets and their airblast sprays of cross-injected
liquid
K. D. Kihm, T. K. Kim, S. Y. Son A
planar and instantaneous visualization study of high-speed
gas jets and their airblast sprays was performed to
qualitatively examine the different atomization performances
of different gas nozzles. For the visualization of high-speed
gas jets (with no liquid injected), Nd:YAG pulsed laser
sheets imaged the clustered vapor molecules in the Rayleigh
range (d<< |
), condensed from the natural humidity during the isentropic gas expansion
through a nozzle. This method visualized both underexpanded
sonic gas jets from a converging nozzle (SN-Type) and
overexpanded supersonic gas jets from a converging-diverging
nozzle (CD-Type). When liquid is cross-injected, the
same laser sheet images the spray droplets of relatively
large sizes (d > 
or d = 
). The present visualization results show that the
SN-Type nozzle develops a wider spray than the CD-Type
nozzle, quite probably because the SN-Type nozzle has
a wider gas jet (in the absence of liquid) than the
CD-Type. Also, the wider spray of the SN-Type nozzle
lowers the probability of droplet coalescence and generates
finer sprays compared to the CD-Type nozzle. These visualization
results qualitatively agree with the previous quantitative
finding of the different atomization characteristics
of the two types of nozzles (Park et al. 1996).