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Old   October 2, 2009, 14:25
Default breakage of liquid stream
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Pei-Ying Hsieh
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Dear CFD experts:

I am working on a case involves liquid jet. Reynolds' # is only about 1. nozzle diameter is less than 1 mm, the average speed is around 1.5 m/s. The liquid stram flows downward. In the experiments, the lqiud stream stay intact, say for about 5 cm, then, starts breaking into drops. However, in my CFD results, the liquid stream started breaking at around 2 cm. In CFD, the liquid stream also showed some in-stabiltiy (swing side to side), while I did not observe this in the experiment.

I have played with different surface tension, different schemes (upwind, limitedLinear..) without much improvements.

It will be appreciated if someone can point to me some literatures on break-ups of liquid stream or make suggestions on how to improve my CFD results.

phsieh2005
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Old   October 5, 2009, 12:57
Default Liquid jet disintegration
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CFDtoy
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Ok. So - here we have a problem of rayleigh instability. For your case - check the viscosity of the liquid (increase it to delay breakup). No problems with surf tension - keep that constant (water - 0.072 etc) The surface tension togehter with viscosity will define droplet diameter and nature of breakup.

this should be straightforward to get good results. Your results are off by more than 50% - Again ! check the fluid properties.

CFDtoy

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Originally Posted by phsieh2005 View Post
Dear CFD experts:

I am working on a case involves liquid jet. Reynolds' # is only about 1. nozzle diameter is less than 1 mm, the average speed is around 1.5 m/s. The liquid stram flows downward. In the experiments, the lqiud stream stay intact, say for about 5 cm, then, starts breaking into drops. However, in my CFD results, the liquid stream started breaking at around 2 cm. In CFD, the liquid stream also showed some in-stabiltiy (swing side to side), while I did not observe this in the experiment.

I have played with different surface tension, different schemes (upwind, limitedLinear..) without much improvements.

It will be appreciated if someone can point to me some literatures on break-ups of liquid stream or make suggestions on how to improve my CFD results.

phsieh2005
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Old   October 5, 2009, 15:19
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Pei-Ying Hsieh
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Thanks CFDtoy!

I will give it a try.

phsieh
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Old   October 5, 2009, 15:22
Default jet breakup
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by the way, i am assuming that you did try different meshes as well. Also, what software or code are you using and the nature of VOF scheme?

/CFDtoy

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Thanks CFDtoy!

I will give it a try.

phsieh
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Old   October 6, 2009, 20:44
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Pei-Ying Hsieh
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Hi, CFDtoy,

I am using OpenFOAM.

Yesterday, I increased the flow domain by 2 times and now the liquid stream did not break, but, still showed some in-stability. In our experiment, the jet is straight and solid within the length we looked at. Maybe I need to increase the flow domain further. Besides the inlet and nozzle wall, I have atmospheric BC all around.

Pei
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