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Droplet generation

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Old   May 27, 2017, 06:37
Default Droplet generation
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Hei guys..
Can anyone please kindly tell me how to simulate a droplet generation in multiphase model? The system is a continuos liquid water flows into nozzle then exit as water droplet. I do really appreciate your help
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Old   June 1, 2017, 05:00
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You can try VOF model. Keep in mind that you need a sufficient mesh resolution to capture the droplet interface. What is your second phase, air?
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Old   June 3, 2017, 23:21
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thank you for replying BlnPhoenix ,

I've tried using VOF and yes the second phase is air, but the flow is still continuous. My geometry is quite big, I am using unstructured mesh and the sizing is 0.01 m, is it not sufficient? If not, can you tell me how small it should be?
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Old   June 4, 2017, 01:47
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Quote:
Originally Posted by woyolo View Post
thank you for replying BlnPhoenix ,

I've tried using VOF and yes the second phase is air, but the flow is still continuous. My geometry is quite big, I am using unstructured mesh and the sizing is 0.01 m, is it not sufficient? If not, can you tell me how small it should be?
In the case you don't need to capture interface between two phases, you can use Eulerian model. Eulerian model Always assumes liquid as continuous phase
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Old   June 4, 2017, 03:33
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Quote:
Originally Posted by SPH_CFD View Post
In the case you don't need to capture interface between two phases, you can use Eulerian model. Eulerian model Always assumes liquid as continuous phase
Does it mean that eulerian model can only model the bubble flow? not the droplet? and what will happens if the volume fraction of the liquid is much less than the air?
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Old   June 4, 2017, 03:38
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Originally Posted by woyolo View Post
Does it mean that eulerian model can only model the bubble flow? not the droplet? and what will happens if the volume fraction of the liquid is much less than the air?
Of course, Eulerian model cannot catch droplets with their interface. However, depends on volume fraction and density each phase, you can know where is droplets (please remember that liquid density is high, water density is approximately 1000)

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Old   June 4, 2017, 05:23
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You could use Multi-Fluid VOF Model in Ansys, which is a hybrid Eulerian-VOF Model. Based on your mesh size it captures the (very) large Droplets of water as VOF, the rest is dispersed Eulerian fraction for which the mesh resolution is not sufficiently small enough.

If you want to model all the detail (interfaces of small, medium droplets) there is unfortunatly no alternative to decrease in mesh size. You will see gradually more detail with every step of mesh refinement with the VOF approach.
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Old   June 5, 2017, 10:30
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Quote:
Originally Posted by woyolo View Post
thank you for replying BlnPhoenix ,

I've tried using VOF and yes the second phase is air, but the flow is still continuous. My geometry is quite big, I am using unstructured mesh and the sizing is 0.01 m, is it not sufficient? If not, can you tell me how small it should be?
I would say that the model you have to choose is strictly related to the droplet's size you're looking for. Do you have any estimation on the size distribution generated by your nozzle?
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