how to determine drag force acting on bubbles in a bubble column?

melj · January 24, 2020, 13:04

Hello

I would like to find the drag force acting on bubbles in a bubble column.

I have tried using drag monitor in Fluent and it calculates drag force for the walls. Is the value obtained using this approach the drag force experienced by bubbles in a bubble column as well?

thank you in advance

vinerm · January 28, 2020, 09:31

Hi

Drag force on bubble can only be predicted if the interface is being resolved, such as with VOF or Dynamic Mesh. With other multiphase models, CFD tools expect Drag coefficient to be provided by the user. If your question is about drag force based on the drag coefficient being used, then you may simply use a Custom Field-Function.

melj · January 28, 2020, 17:08

Thank you vinerm. So i am using Eulerian multiphase model. The drag force that I calculate using the drag monitor on the wall would be calculated by Fluent using the drag coefficient being used by Fluent rite? I am not familiar with UDF in Fluent.

vinerm · January 29, 2020, 04:33

Drag on the wall has got nothing to do with drag coefficient being used for the interphase interaction. Drag on the wall is being determined from the first principle, i.e., by using the solved velocity field.

On the other hand, drag interaction between the phases is different. Since your interest lies in predicting the drag on the bubble in the bubble column, you have to either use VOF or you have to create bubbles of various shapes as solid geometries and then monitor the drag on the bubble boundaries. If the shapes of the bubbles are known, then you do not need CFD. You can use correlations, such as Grace's or Tomiyama's. The interest, most of the time, in doing a bubble column simulation lies in predicting the gas hold-up, dispersion coefficient, etc. but not in predicting drag. That part is usually done either using DNS or experiments.

melj · January 29, 2020, 13:31

Thank you so much. Your comments were very helpful.

melj · January 29, 2020, 13:45

So if I knew the bubble shape, I could use the existing correlations to create a custom field function to obtain the value from CFD. Is that rite? Or did you mean using the correlations in DNS or experiments? Apologies if I have got it completely wrong.

vinerm · January 30, 2020, 03:43

If the shape is known, you do not require CFD. Drag coefficients are usually given in terms of known parameters.

melj · January 30, 2020, 11:54

Got it. Thank you.

farzadmech · September 4, 2020, 15:02

Dear Friends
Has anyone used Lagrangian Particle Tracking for simulation of Bubble Plume. What Drag model is acceptable for bubbles?

Thanks,
Farzad

January 24, 2020, 13:04	how to determine drag force acting on bubbles in a bubble column?	#1
melj Member mln Join Date: Dec 2019 Posts: 39 Rep Power: 7	Hello I would like to find the drag force acting on bubbles in a bubble column. I have tried using drag monitor in Fluent and it calculates drag force for the walls. Is the value obtained using this approach the drag force experienced by bubbles in a bubble column as well? thank you in advance

January 28, 2020, 09:31	Depends on model	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	Hi Drag force on bubble can only be predicted if the interface is being resolved, such as with VOF or Dynamic Mesh. With other multiphase models, CFD tools expect Drag coefficient to be provided by the user. If your question is about drag force based on the drag coefficient being used, then you may simply use a Custom Field-Function. melj likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

January 29, 2020, 04:33	Both are different	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	Drag on the wall has got nothing to do with drag coefficient being used for the interphase interaction. Drag on the wall is being determined from the first principle, i.e., by using the solved velocity field. On the other hand, drag interaction between the phases is different. Since your interest lies in predicting the drag on the bubble in the bubble column, you have to either use VOF or you have to create bubbles of various shapes as solid geometries and then monitor the drag on the bubble boundaries. If the shapes of the bubbles are known, then you do not need CFD. You can use correlations, such as Grace's or Tomiyama's. The interest, most of the time, in doing a bubble column simulation lies in predicting the gas hold-up, dispersion coefficient, etc. but not in predicting drag. That part is usually done either using DNS or experiments. melj and waelajaber like this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

January 30, 2020, 03:43	CFD not required	#7
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	If the shape is known, you do not require CFD. Drag coefficients are usually given in terms of known parameters. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

September 4, 2020, 15:02	lagrangian Particle Tracking(Bubbles)	#9
farzadmech Senior Member Farzad Faraji Join Date: Nov 2019 Posts: 206 Rep Power: 8	Dear Friends Has anyone used Lagrangian Particle Tracking for simulation of Bubble Plume. What Drag model is acceptable for bubbles? Thanks, Farzad

January 28, 2020, 17:08		#3
melj Member mln Join Date: Dec 2019 Posts: 39 Rep Power: 7	Thank you vinerm. So i am using Eulerian multiphase model. The drag force that I calculate using the drag monitor on the wall would be calculated by Fluent using the drag coefficient being used by Fluent rite? I am not familiar with UDF in Fluent.

January 29, 2020, 13:31		#5
melj Member mln Join Date: Dec 2019 Posts: 39 Rep Power: 7	Thank you so much. Your comments were very helpful.

January 29, 2020, 13:45		#6
melj Member mln Join Date: Dec 2019 Posts: 39 Rep Power: 7	So if I knew the bubble shape, I could use the existing correlations to create a custom field function to obtain the value from CFD. Is that rite? Or did you mean using the correlations in DNS or experiments? Apologies if I have got it completely wrong.

January 30, 2020, 11:54		#8
melj Member mln Join Date: Dec 2019 Posts: 39 Rep Power: 7	Got it. Thank you.

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