VOF/Capillary Rise has incorrect height

AshleyB · August 27, 2015, 12:37

Hey there

I am doing a 2-d axi-symmetric case with water in a capillary. I'm just trying to verify against the Lucas-Washburn equation. Water is going much, much farther in the capillary than the analytical solution. It is not even close.

-My mesh is on the +x-axis, gravity in the -x-axis.
-Using VOF model, explicit scheme
-Piso coupling
-Courant number is 0.6 which lead to t~1e-6 which I feel is sufficiently small
-Surface Tension 0.07 N/m
-Contact angle 70 degrees
-Pipe radius of 0.3 mm
-Pressure Inlet and pressure outlet are both at gauge 0

This should go about 16 mm, but it does not. Does anyone have any idea why?

Also, what is an acceptable residual for this problem?

Thanks in advance for any help.

guigui2209 · April 28, 2016, 13:36

Hi, did you find a solution for your problem? I'm doing the same case and for me it's the opposite, in the simulation water is much lower than in the lucas-washburn equation. I have almost the same configuration as you have, but instead of 70 degrees I have 0 because is the contact angle between water and glass

AshleyB · April 28, 2016, 15:25

Andrea

In the operating conditions I clicked the operating density box and put in the density of air. After reading fluent guides, if I am not mistaken, if you do not click this box it will automatically take the average over cells, which for water and air would be totally inaccurate. Hopefully this helps, otherwise there may be a problem with initial conditions. Good luck!

August 27, 2015, 12:37	VOF/Capillary Rise has incorrect height	#1
AshleyB New Member Ashley Byers Join Date: Jan 2015 Posts: 3 Rep Power: 11	Hey there I am doing a 2-d axi-symmetric case with water in a capillary. I'm just trying to verify against the Lucas-Washburn equation. Water is going much, much farther in the capillary than the analytical solution. It is not even close. -My mesh is on the +x-axis, gravity in the -x-axis. -Using VOF model, explicit scheme -Piso coupling -Courant number is 0.6 which lead to t~1e-6 which I feel is sufficiently small -Surface Tension 0.07 N/m -Contact angle 70 degrees -Pipe radius of 0.3 mm -Pressure Inlet and pressure outlet are both at gauge 0 This should go about 16 mm, but it does not. Does anyone have any idea why? Also, what is an acceptable residual for this problem? Thanks in advance for any help.

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April 28, 2016, 13:36		#2
guigui2209 New Member Andrea Join Date: Dec 2015 Posts: 1 Rep Power: 0	Hi, did you find a solution for your problem? I'm doing the same case and for me it's the opposite, in the simulation water is much lower than in the lucas-washburn equation. I have almost the same configuration as you have, but instead of 70 degrees I have 0 because is the contact angle between water and glass

April 28, 2016, 15:25		#3
AshleyB New Member Ashley Byers Join Date: Jan 2015 Posts: 3 Rep Power: 11	Andrea In the operating conditions I clicked the operating density box and put in the density of air. After reading fluent guides, if I am not mistaken, if you do not click this box it will automatically take the average over cells, which for water and air would be totally inaccurate. Hopefully this helps, otherwise there may be a problem with initial conditions. Good luck!