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Analysis method of spray mist in CFX

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Old   June 29, 2022, 06:09
Default Analysis method of spray mist in CFX
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Takayuki SUzuki
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Dear all,

I am trying to use CFX to do an analysis on how mist spreads when water is sprayed through a single nozzle into the air as shown in the figure, but the results seem to be wrong. Please advise.
The model is a nozzle with a simple orifice geometry as shown in the figure.
The main settings of CFX are as follows

Air: Continuous fluid
Water: Dispersed Fluid (300 micron)
Free surface model: Standard
Fluids Pair Models: Surface Tension Coefficient

Inlet: Total pressure (Volume Fraction, Air:0, Water:1)
outelt:Opening (Volume Fraction, Air:1, Water:0)

Since only water flows in at the inlet, water must be 100% in the nozzle, but the water volume fraction in the nozzle cross-section is not equal to 1. At the inlet boundary, the water volume fraction was completely 1.
Note that we have not included a cavitation model, but the maximum flow velocity is about 10 m/s, so we do not expect cavitation to occur.
Also, looking at the Air Velocity, the situation has a velocity distribution even inside the nozzle.

Is the setting wrong to begin with?
Any advice on the proper settings for how to analyze how 100% of the water flows into the nozzle and disperses into the atmosphere would be helpful.

Thank you,
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Old   July 4, 2022, 04:17
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1) You should initialiize your CFD calculations such that the whole nozzle is filled with water and the surrounding is filled with air. It looks lie you didn't do that.

2) The air velocity shows the velocity that air will have at any location, even it the volume fraction is 1e-10. The same for water velocity. This shows the the velocity for any volume fraction of water, even it would be 1e-10. I guess you are looking for superficial velocities. This is the Velocity*Volume fraction. You can find this variable when clicking on the "..."
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