Buoyancy force of second phase in Eulerian model

amin.z · March 7, 2015, 13:05

Hi friends

I wanna know in Eulerian multiphase model, how fluent calculates the buoyancy force of second phase!? is there any official document or equation to describe it?

`e` · March 12, 2015, 06:59

I have checked the gravity/buoyancy force for the second phase using the Lagrangian reference frame (DPM), and Fluent's built-in code agrees with my UDF code.

Is there a particular reason you are concerned with how Fluent handles gravity/buoyancy? If you're unsure of the theory behind this force, check out this post on a physics forum.

amin.z · March 12, 2015, 07:12

Quote:

Originally Posted by `e`

I have checked the gravity/buoyancy force for the second phase using the Lagrangian reference frame (DPM), and Fluent's built-in code agrees with my UDF code.

Is there a particular reason you are concerned with how Fluent handles gravity/buoyancy? If you're unsure of the theory behind this force, check out this post on a physics forum.

hi
thanks for your answer
I know about buoyancy force but the question is about fluent solving procedure!
Fluent solves only a few equations! no further things!
I want to know in Eulerian multiphase model, how fluent calculates the effect of buoyancy force? where is the buoyancy terms? only in momentum equations? or...

`e` · March 12, 2015, 22:13

Yes, I know you were after the Eulerian model. I've only experience with the DPM but suspect Fluent has a similar approach for handling the gravity/buoyancy effects with their Eulerian model. You could turn gravity off and write a gravity/buoyancy source term UDF to handle these effects in your own way (or to check Fluent's implementation is correct, as I have done with the DPM).

Have you read the User Guide and Theory guide? There are a few sections on inclusion of gravity effects by the looks which might answer your question. Are you getting erroneous results with your second phase or what's happening?

amin.z · March 14, 2015, 02:51

I don't want write a UDF for my simple problem!
In fact, I've used Eulerian model and my problem has converged but my advisor has a doubt about calculation of bouyancy force by fluent. as you, his expert is in DPM.

and another question about phase interaction tabs! I' modelling a bubble column. the problem is in "turbulent dispersion" tab. my advisor suggest me to use "Lopez-de-bertodano" but in this condition, the solution is very unstable and finally lead to divergence! but by another model it's very stable and easily converge!
what's your opinion? do you know a reference to explain these models!?

Thanks

`e` · March 14, 2015, 05:13

It would take perhaps five minutes to write and test the UDF to ensure the buoyancy/gravity calculations are correct. This task is not complicated or lengthy, it's simply a DEFINE_SOURCE macro.

I'm not familiar with these models but if one works then I'd go with that one. I recommend reading literature on these models because they appear very case specific (you might get lucky with an informed forum member replying though); best of luck!

amin.z · March 16, 2015, 09:14

Thanks
In fact, I would like to find out equations which solved by fluent

March 7, 2015, 13:05	Buoyancy force of second phase in Eulerian model	#1
amin.z Senior Member Amin Join Date: Oct 2013 Location: Germany Posts: 397 Rep Power: 15	Hi friends I wanna know in Eulerian multiphase model, how fluent calculates the buoyancy force of second phase!? is there any official document or equation to describe it?

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March 12, 2015, 06:59		#2
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	I have checked the gravity/buoyancy force for the second phase using the Lagrangian reference frame (DPM), and Fluent's built-in code agrees with my UDF code. Is there a particular reason you are concerned with how Fluent handles gravity/buoyancy? If you're unsure of the theory behind this force, check out this post on a physics forum.

March 12, 2015, 22:13		#4
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	Yes, I know you were after the Eulerian model. I've only experience with the DPM but suspect Fluent has a similar approach for handling the gravity/buoyancy effects with their Eulerian model. You could turn gravity off and write a gravity/buoyancy source term UDF to handle these effects in your own way (or to check Fluent's implementation is correct, as I have done with the DPM). Have you read the User Guide and Theory guide? There are a few sections on inclusion of gravity effects by the looks which might answer your question. Are you getting erroneous results with your second phase or what's happening?

March 14, 2015, 02:51		#5
amin.z Senior Member Amin Join Date: Oct 2013 Location: Germany Posts: 397 Rep Power: 15	I don't want write a UDF for my simple problem! In fact, I've used Eulerian model and my problem has converged but my advisor has a doubt about calculation of bouyancy force by fluent. as you, his expert is in DPM. and another question about phase interaction tabs! I' modelling a bubble column. the problem is in "turbulent dispersion" tab. my advisor suggest me to use "Lopez-de-bertodano" but in this condition, the solution is very unstable and finally lead to divergence! but by another model it's very stable and easily converge! what's your opinion? do you know a reference to explain these models!? Thanks

March 14, 2015, 05:13		#6
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	It would take perhaps five minutes to write and test the UDF to ensure the buoyancy/gravity calculations are correct. This task is not complicated or lengthy, it's simply a DEFINE_SOURCE macro. I'm not familiar with these models but if one works then I'd go with that one. I recommend reading literature on these models because they appear very case specific (you might get lucky with an informed forum member replying though); best of luck!

March 16, 2015, 09:14		#7
amin.z Senior Member Amin Join Date: Oct 2013 Location: Germany Posts: 397 Rep Power: 15	Thanks In fact, I would like to find out equations which solved by fluent