About the turbulence model?

whiz · July 10, 2009, 11:10

Hello, all.
How to choose the turbulence model when using CFX?
for flow in foam materials:
Re<1, Darcy or viscous-drag, dominated flow
1~10<Re<150, Forchheimer, or form-drag, dominated flow
150<Re<300, post-Forchheimer (unsteady laminar flow)
Re>300, fully trubulent flow.

How to choose the model when Re in the range of 100~300?
I am using CFX11.0.

ghorrocks · July 11, 2009, 09:16

Hi,

What turbulence model to use for a transitional foamy flow? Good luck! There is no way a standard turbulence model is going to work in this case. Turbulence modelling of transitional flows is an area of active research (but models such as Menter's SST turbulence transition model show that for some areas it is quite mature) and multiphase turbulence modelling is another area of active research (but is far less mature).

You are going to have to do a lot of validation and verification. I would start with a simple laminar flow and compare to experimental results and see how close you are. If it is no good then try some models which work well in low Re regimes such as k-w or possibly SST.

There are no simple answers to your question.

Glenn Horrocks

whiz · July 12, 2009, 08:49

Dear Glenn,
I can't compare the results with the experimental results, I have not experimental results.
I find there is huge difference of the temperature field between the laminar flow and turbulence flow.

I think the results of SST model is better.
How to choose the transitional turbulence, when I use the sst (shear stress transport) model.
there are four choice:
fully turbulent
specified intermittency
gamma model
gamma theta model
Thanks

ghorrocks · July 12, 2009, 20:37

Hi,

None of the default turbulence options will be acceptable without checking. You will need to get some form of validation case to check the model against to have even the faintest hope of getting an accurate answer.

If you can't do experimental work on the thing you are modelling then try to get something which is close from the literature. You will need SOMETHING to validate the various models against.

Glenn Horrocks

July 10, 2009, 11:10	About the turbulence model?	#1
whiz New Member wu Join Date: Jul 2009 Posts: 14 Rep Power: 17	Hello, all. How to choose the turbulence model when using CFX? for flow in foam materials: Re<1, Darcy or viscous-drag, dominated flow 1~10<Re<150, Forchheimer, or form-drag, dominated flow 150<Re<300, post-Forchheimer (unsteady laminar flow) Re>300, fully trubulent flow. How to choose the model when Re in the range of 100~300? I am using CFX11.0.

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July 11, 2009, 09:16		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	Hi, What turbulence model to use for a transitional foamy flow? Good luck! There is no way a standard turbulence model is going to work in this case. Turbulence modelling of transitional flows is an area of active research (but models such as Menter's SST turbulence transition model show that for some areas it is quite mature) and multiphase turbulence modelling is another area of active research (but is far less mature). You are going to have to do a lot of validation and verification. I would start with a simple laminar flow and compare to experimental results and see how close you are. If it is no good then try some models which work well in low Re regimes such as k-w or possibly SST. There are no simple answers to your question. Glenn Horrocks

July 12, 2009, 08:49		#3
whiz New Member wu Join Date: Jul 2009 Posts: 14 Rep Power: 17	Dear Glenn, I can't compare the results with the experimental results, I have not experimental results. I find there is huge difference of the temperature field between the laminar flow and turbulence flow. I think the results of SST model is better. How to choose the transitional turbulence, when I use the sst (shear stress transport) model. there are four choice: fully turbulent specified intermittency gamma model gamma theta model Thanks

July 12, 2009, 20:37		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	Hi, None of the default turbulence options will be acceptable without checking. You will need to get some form of validation case to check the model against to have even the faintest hope of getting an accurate answer. If you can't do experimental work on the thing you are modelling then try to get something which is close from the literature. You will need SOMETHING to validate the various models against. Glenn Horrocks