VOF does not show a sharp interface

stanlee8 · June 27, 2021, 07:15

Hi everyone,

I am trying to simulate the natural evaporation of a thin water film. Basically, there is dry air passing through above the water liquid film, and the water liquid is expected to evaporate into the dry air.

I used VOF and enabled the sharp interface and interfacial anti-diffusion, as well the evaporation-condensation Lee model.

However, as the picture shows, the interface between the water liquid and the air (the air is the mixture of water vapour and dry air) is not "sharp" at all. Instead, there is a gradient of volume fraction of water liquid. How could this be? I expected the interface should only occupy one layer of cells, which mean except for one layer of cells, other cells should be either 0 volume fraction of water liquid or 1 volume fraction.

Could somebody please help? Thanks

Regards

LoGaL · June 27, 2021, 16:55

You are using interpolation in the contour, you should check cell values instead.
Substantially, if in one cell your volume fraction is 1 and in the next is 0, if you use interpolation in the contour, you will see a gradient from 1 to 0, if you show cell values, this does not happen

stanlee8 · June 27, 2021, 18:41

Dear LoGap,
Thanks for your comments, but could you please tell me how I can check the cell values?

LoGaL · June 28, 2021, 04:08

I think you should disable “node values” before plotting the contour

stanlee8 · June 28, 2021, 04:39

Cool, I have tried it up and it seems to work.
Let's c what will happen.
Thank you!

June 27, 2021, 07:15	VOF does not show a sharp interface	#1
stanlee8 New Member Stanlee Join Date: Aug 2017 Location: New Zealand Posts: 19 Rep Power: 8	Hi everyone, I am trying to simulate the natural evaporation of a thin water film. Basically, there is dry air passing through above the water liquid film, and the water liquid is expected to evaporate into the dry air. I used VOF and enabled the sharp interface and interfacial anti-diffusion, as well the evaporation-condensation Lee model. However, as the picture shows, the interface between the water liquid and the air (the air is the mixture of water vapour and dry air) is not "sharp" at all. Instead, there is a gradient of volume fraction of water liquid. How could this be? I expected the interface should only occupy one layer of cells, which mean except for one layer of cells, other cells should be either 0 volume fraction of water liquid or 1 volume fraction. Could somebody please help? Thanks Regards

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June 27, 2021, 16:55		#2
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	You are using interpolation in the contour, you should check cell values instead. Substantially, if in one cell your volume fraction is 1 and in the next is 0, if you use interpolation in the contour, you will see a gradient from 1 to 0, if you show cell values, this does not happen

June 27, 2021, 18:41		#3
stanlee8 New Member Stanlee Join Date: Aug 2017 Location: New Zealand Posts: 19 Rep Power: 8	Dear LoGap, Thanks for your comments, but could you please tell me how I can check the cell values?

June 28, 2021, 04:08		#4
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 375 Rep Power: 12	I think you should disable “node values” before plotting the contour

June 28, 2021, 04:39		#5
stanlee8 New Member Stanlee Join Date: Aug 2017 Location: New Zealand Posts: 19 Rep Power: 8	Cool, I have tried it up and it seems to work. Let's c what will happen. Thank you!