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Old   March 20, 2009, 20:55
Default low reynolds number K-epsilon model
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amar
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Dear

I need to know which turbulence model in Fluent is equivalent to the low Reynolds number K-epsilon model available in Star-CD.

I appreciate your answer and I'm looking forward for your reply.
Thanks a lot.
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Old   March 21, 2009, 08:37
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Janarthanan Alagesan
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The below mentioned models are the low reynolds number k -e models available in Fluent. I am not sure which one used in Star - CD since I never used it. Hope this may give some information.

Index Model
0 Abid
1 Lam-Bremhorst
2 Launder-Sharma
3 Yang-Shih
4 Abe-Kondoh-Nagano
5 Chang-Hsieh-Chen

Cheers,
Alagesanj
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Old   March 21, 2009, 12:29
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Dear Alagesanj
Thank you very much for your your reply

I'm doing my simulation using Fluent 6.3 and I have found just three types of K-epsilon models as follow

1- standard
2- RNG
3- Realizable

May you tell me how to choose any of the Reynolds number you mentioned.

Thanks a lot

Quote:
Originally Posted by Alagesanj View Post
The below mentioned models are the low reynolds number k -e models available in Fluent. I am not sure which one used in Star - CD since I never used it. Hope this may give some information.

Index Model
0 Abid
1 Lam-Bremhorst
2 Launder-Sharma
3 Yang-Shih
4 Abe-Kondoh-Nagano
5 Chang-Hsieh-Chen

Cheers,
Alagesanj
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Old   March 21, 2009, 17:11
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The low-Re models mentioned by Algesanj are only available from the text interface and can not be selected via the gui. If I remember correctly you need to select "turbulence expert" or something like that in the text interface to display these models. The manual for starcd should give the name of the model they use. I would still recommend you to use the two-layer Wolfstein model that is selectable through the gui (extended wall treatment it used to be called I think, I'm not using Fluent that much these days so things might have changed). Of the low-Re models I would recommend the Yang-Shih model.
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Old   March 22, 2009, 10:07
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Hi Amar,

What Jonas mentioned is correct. These low re k-e models I mentioned are not available from the GUI.

I am thankful to Mr. Jonas since I got to know some very important CFD basics from his previous (very old) posts. Even this low re ke models also I came to know from his post only.

After you select the k-e model in the GUI you can access the low re k-e models by typing

define/models/viscous/turbulenceexpert/lowreke

then enter. When the command prompt asks for "Enable the low-Re k-epsilon turbulence model? [no]" type 'yes'. Now you can see the low re ke model in your GUI.

then again type
define/models/viscous/turbulenceexpert/lowrekeindex

you will be prompted to enter the index number

the index number represents the corresponding low re ke model which i have mentioned in my previous post.

Hope this will help.

Cheers, Alagesan.
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Old   March 22, 2009, 13:44
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Thanks for those nice words Alagesan. Did you make any comparison between the low-Re models available in Fluent? Which one would you choose as your first alternative?
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Old   March 23, 2009, 03:18
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Hello

I'd like to thank mister Jonas and Alagesan for their help and quick answers of my question, I really thankful.
I'm now testing the second model (index-1) but I didn't get good results. Actually I also need to know how to do energy unbalance test.

Thanks a lot .
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Old   March 25, 2009, 04:48
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Quote:
Originally Posted by amar View Post
Dear

I need to know which turbulence model in Fluent is equivalent to the low Reynolds number K-epsilon model available in Star-CD.

I appreciate your answer and I'm looking forward for your reply.
Thanks a lot.
hello

I've just read your mails and was happy to find them : i've found an example of the use of fluent in low-reynolds here : http://www.sciencedirect.com/science...14f24c7a85341e

it can interest you ?
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Old   March 25, 2009, 08:56
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Dear Laurence Wallian

Thank you very much for your reply, sure this paper will help me.
Also I'd like to ask you if you know how to calculate or do the energy balance test.
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Old   March 25, 2009, 10:55
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hello,

I'm sorry, but I don't what is the "energy balance test"

I hope someone can reply you
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Old   March 25, 2009, 17:06
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hello amar,

using any one of the low reynolds' number turbulence model from the TUI is ok, but it would be better if you can modify the low reynolds k-omega model itself.
at one time, i had worked on it. but of course, it all depends what and why you want it.
best regards,

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Old   March 25, 2009, 18:33
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Dear

Thanks a lot for your reply.
What do you mean by modify the low Reynold number and how, please?

I appreciate your help.
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Old   March 26, 2009, 04:38
Default k-omega model
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Both k- omega models (std and sst) are available as low-Reynolds-number models as well as high-Reynolds-number models.

The wall boundary conditions for the k equation in the k- omega models are treated in the same way as the k equation is treated when enhanced wall treatments are used with the k- epsilon models.



In my opinion, the Launder and Sharma etc. low Re turb. models essentially linear whereas this low Re k-omega model is non-linear.

you can model transitional flows better with this k-omega model.

A good paper on k-omega model is:
"A half century historical review of the k-omega model"


basically, you need to know what is your nature of the problem.
if you have need to have transitonal behaviour, you can check both the low-Re k-epsilon and k-omega models.

best wishes.
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Old   March 26, 2009, 04:53
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Dear rana

I really thankful for your answers and your interest to solve my problem.
May I continue send questions to you because I'm new in using Fluent just two months ago and I need to solve my simulation as soon as possible.

Thanks a lot
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Old   March 26, 2009, 04:55
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ok amar, ask me.
if you have too confidential queries, you may also contact me confidentially.
my mail id is royrana123@yahoo.com
i will try my bnest to help you.

thanks.
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Old   March 26, 2009, 23:52
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Hi Rana,

I just want to clarify some doubts regarding the low re k- w model.

My apology to Amar since I am intruding in his thread.

I am analysing a 2D airfoil flow at low reynolds number i.e. around 0.1 million to 0.5 million. I used both k-e and k-w models. SST k-w model with transitional flow (low re k-w model) performed better than the k-e models available in the GUI. But it often failed to predit the transition of laminar to turbulence and drag result shows errror of around 20 to 30%.

So finally i used forced transition model and again it was very difficult to get a converged solution.

You have mentioned that by modifying the low re k-w model itself can give better results. If it is possible can you guide me on this part.

Thanks,
Alagesan.
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Old   March 27, 2009, 04:49
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yes, probably i can help in this case.
send me a mail so that i can send you the thesis.
thanks and regards.
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Old   June 16, 2009, 09:16
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Hi,

I am modeling a single phase flow is a circular tube, where the Reynolds number is between 1000-6000, and I am looking for a single turbulence model capable to predict the shear stress accurately in laminar, transition and turbulent regime compared to theoretical equations.

So I wonder if you have any suggestion in using a particular low-Re k-epsilon turbulent model, or k-omega and which will be the best performing model.

Thanks for the help.
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Old   April 16, 2010, 12:11
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thank you very much for your guidance, it works
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Old   April 16, 2010, 12:15
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Quote:
Originally Posted by Alagesanj View Post
Hi Amar,

What Jonas mentioned is correct. These low re k-e models I mentioned are not available from the GUI.

I am thankful to Mr. Jonas since I got to know some very important CFD basics from his previous (very old) posts. Even this low re ke models also I came to know from his post only.

After you select the k-e model in the GUI you can access the low re k-e models by typing

define/models/viscous/turbulenceexpert/lowreke

then enter. When the command prompt asks for "Enable the low-Re k-epsilon turbulence model? [no]" type 'yes'. Now you can see the low re ke model in your GUI.

then again type
define/models/viscous/turbulenceexpert/lowrekeindex

you will be prompted to enter the index number

the index number represents the corresponding low re ke model which i have mentioned in my previous post.

Hope this will help.

Cheers, Alagesan.


THANK YOU VERY MUCH Alagesanj FOR YOUR ORIENTATION
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