interface tension question with interFoam solver

openTom · May 29, 2009, 11:03

Hi Foamers,
i'm trying to set up several testcases for the interFoam solver at the moment, in order to analyze it with respect to e.g. gravity currents.
The surface tension in an air water system can be set with the sigma term under transportProperties to a value of 0.07 kg/s².
But for the case of having a closed box with two liquids (in contact) inside i will have to define two values of surface tension or one value of interface tension, i think?! Is it right then to take only the difference of the two surface tension values and store it under the sigma term in the transport properties?
Let's say i'm using a water and saltwater system which is normally miscible (but interfoam treats it as unmiscible), so i should have to set the sigma to zero, right?
Thanks

caw · May 29, 2009, 11:42

Hi,

surface tension is a specific property for a given system, eg. air-water (thats the 0.072). Once you have a different system like water-oil you have to use measured values for this system.

Btw: i would think that the interfoam solver is not appropriate for a case with MISCIBLE fluids. you might want to try a different approach.

best regrads
christian

openTom · May 29, 2009, 12:19

Thank's for your reply.
The important fact in my case is the density difference of the two liquids. In my case this is about 5kg/m³. The liquids should be treated as unmiscible, that's why i'm using interFoam, but here is the problem. Since water and saltwater are miscible, the interface tension should be zero. Please correct me if I'm wrong. Is interFoam solving right, if i use a sigma with the value zero? I could also set a hypothetical value of let's say 0.001 to keep the liquids unmiscible.
The best would probably be to investigate an unmiscible water oil system where the interface tension is known, but the saltwater-water case was solved with an other cfd software and i want to compare the results.

caw · May 29, 2009, 14:00

Ok, i understand. Setting sigma to zero is not a problem at all. it simple switches of an additional source term in the momentum balance, that accounts for the surface tension at the phase interface (0< gamma<1).

The force caused by surface tension is modelled my a CSF model. CSF = continuum surface force.
This converts the surface force into a volume force, which can be included into our FVM.

Best regards
christian

openTom · May 29, 2009, 14:18

Thank you.

May 29, 2009, 11:03	interface tension question with interFoam solver	#1
openTom New Member Join Date: May 2009 Posts: 13 Rep Power: 17	Hi Foamers, i'm trying to set up several testcases for the interFoam solver at the moment, in order to analyze it with respect to e.g. gravity currents. The surface tension in an air water system can be set with the sigma term under transportProperties to a value of 0.07 kg/s². But for the case of having a closed box with two liquids (in contact) inside i will have to define two values of surface tension or one value of interface tension, i think?! Is it right then to take only the difference of the two surface tension values and store it under the sigma term in the transport properties? Let's say i'm using a water and saltwater system which is normally miscible (but interfoam treats it as unmiscible), so i should have to set the sigma to zero, right? Thanks

May 29, 2009, 14:00		#4
caw Member Christian Winkler Join Date: Mar 2009 Location: Mannheim, Germany Posts: 63 Rep Power: 17	Ok, i understand. Setting sigma to zero is not a problem at all. it simple switches of an additional source term in the momentum balance, that accounts for the surface tension at the phase interface (0< gamma<1). The force caused by surface tension is modelled my a CSF model. CSF = continuum surface force. This converts the surface force into a volume force, which can be included into our FVM. Best regards christian Pirlu and fredup like this.

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May 29, 2009, 11:42		#2
caw Member Christian Winkler Join Date: Mar 2009 Location: Mannheim, Germany Posts: 63 Rep Power: 17	Hi, surface tension is a specific property for a given system, eg. air-water (thats the 0.072). Once you have a different system like water-oil you have to use measured values for this system. Btw: i would think that the interfoam solver is not appropriate for a case with MISCIBLE fluids. you might want to try a different approach. best regrads christian

May 29, 2009, 12:19		#3
openTom New Member Join Date: May 2009 Posts: 13 Rep Power: 17	Thank's for your reply. The important fact in my case is the density difference of the two liquids. In my case this is about 5kg/m³. The liquids should be treated as unmiscible, that's why i'm using interFoam, but here is the problem. Since water and saltwater are miscible, the interface tension should be zero. Please correct me if I'm wrong. Is interFoam solving right, if i use a sigma with the value zero? I could also set a hypothetical value of let's say 0.001 to keep the liquids unmiscible. The best would probably be to investigate an unmiscible water oil system where the interface tension is known, but the saltwater-water case was solved with an other cfd software and i want to compare the results.

May 29, 2009, 14:18		#5
openTom New Member Join Date: May 2009 Posts: 13 Rep Power: 17	Thank you.