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Old   January 14, 2014, 20:09
Question Want to implement a turbuence model! How?
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David
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My advisor want me to implement a 2-equation turbulence model, like K-W or K-E, I am wondering those two equations, should I simultaneously solve them together with N-S equations?

Or, can I solve N-S equation firstly, and then treat the flow field as stable field, and then only calculate k-E equations for the fluctuating variables.

Normally, how do you guys do it? Thanks.
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Old   January 15, 2014, 17:25
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Hi David,

I would be curious to know how you will handle the clousure problem. AFAIK u need to related the unkonw Reynolds stresses to the known mean flow variabes through the turbulent transport equations. The latest can be 1eq. models, 2eq. model or second clousures.

U must end up with:
Full NS eq. - Averaged NS eq. = eq. for fluctuations.

Regards,
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Old   January 16, 2014, 12:46
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Martin Hegedus
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In general, the turbulence model is decoupled from the N.S. equations during the solution process.
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Old   January 17, 2014, 00:51
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Hi!!
This is how I had implemented k-e model
1. Initialize some velocity field.

2. Calculate k.
3. Calculate epsilon
4. Calculate turb viscosity.
5. solve NS to get new velocity field.
6. if velocity < stopping criteria, goto 2, else stop.

If you have any doubts, please reply back!!
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Old   January 17, 2014, 01:38
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A note, from what I understand, the two equation models are finicky about how the convection terms are discritized. The SA model is forgiving, so first order upwind is OK. Also, the two equation implicit methods are a little more tricky, assuming of course that an implicit method is used.
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Old   January 17, 2014, 12:45
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David
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Quote:
Originally Posted by samurai_01 View Post
Hi!!
This is how I had implemented k-e model
1. Initialize some velocity field.

2. Calculate k.
3. Calculate epsilon
4. Calculate turb viscosity.
5. solve NS to get new velocity field.
6. if velocity < stopping criteria, goto 2, else stop.

If you have any doubts, please reply back!!

THanks for all.

When calculating k and epsilon, what algorithm can I use? for example, if I used SIMPLE for velocity field, do I need do any special treatment for the K and E equations? Thanks.
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Old   January 19, 2014, 01:03
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Hi, I'm also trying to update my laminar code to turbulent. I'm reading Wilcox's turbulence modeling for CFD. Is there any books or online material which details the steps for a novice to follow?
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Old   January 19, 2014, 02:20
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Quote:
When calculating k and epsilon, what algorithm can I use? for example, if I used SIMPLE for velocity field, do I need do any special treatment for the K and E equations?
No there shall be no special treatment for that. just do the numerical discretization and apply Tri Diagonal Matrix algo if solving using FDM or go for regular explicit/implicit time stepping for the same. just remember that for collocated FVM grid, you will be required to substitute variables such as effective viscosity at face center rather than going for cell centers.

Give me some time, and i'll upload a document regarding the same, just remind me once after wednesday

Quote:
I'm also trying to update my laminar code to turbulent. I'm reading Wilcox's turbulence modeling for CFD. Is there any books or online material which details the steps for a novice to follow?
I think Wilcox is the best for numerical techniques, but also have a look at Turbulent flow by Eswaran and Biswas, and also refer Peric's book on cfd.
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Old   January 19, 2014, 13:40
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Quote:
Originally Posted by samurai_01 View Post
No there shall be no special treatment for that. just do the numerical discretization and apply Tri Diagonal Matrix algo if solving using FDM or go for regular explicit/implicit time stepping for the same. just remember that for collocated FVM grid, you will be required to substitute variables such as effective viscosity at face center rather than going for cell centers.

Give me some time, and i'll upload a document regarding the same, just remind me once after wednesday



I think Wilcox is the best for numerical techniques, but also have a look at Turbulent flow by Eswaran and Biswas, and also refer Peric's book on cfd.
Thanks, I'll read those for details, and hope you can upload those soon. Thank you very much!
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