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-   -   low reynolds number K-epsilon model (http://www.cfd-online.com/Forums/fluent/62827-low-reynolds-number-k-epsilon-model.html)

amar March 20, 2009 20:55

low reynolds number K-epsilon model
 
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.

Alagesanj March 21, 2009 08:37

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

amar March 21, 2009 12:29

Thanks a lot
 
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 (Post 210217)
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


jola March 21, 2009 17:11

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.

Alagesanj March 22, 2009 10:07

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.

jola March 22, 2009 13:44

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?

amar March 23, 2009 03:18

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 .

Laurence Wallian March 25, 2009 04:48

Quote:

Originally Posted by amar (Post 210195)
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 ?

amar March 25, 2009 08:56

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.

Laurence Wallian March 25, 2009 10:55

hello,

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

I hope someone can reply you

rr123 March 25, 2009 17:06

my suggestion
 
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,

rr123

amar March 25, 2009 18:33

Thanks
 
Dear

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

I appreciate your help.

rr123 March 26, 2009 04:38

k-omega model
 
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.

amar March 26, 2009 04:53

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

rr123 March 26, 2009 04:55

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.

Alagesanj March 26, 2009 23:52

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.

rr123 March 27, 2009 04:49

yes, probably i can help in this case.
send me a mail so that i can send you the thesis.
thanks and regards.

niriosrat June 16, 2009 09:16

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.

gina April 16, 2010 12:11

thank you very much for your guidance, it works:)

gina April 16, 2010 12:15

Quote:

Originally Posted by Alagesanj (Post 210278)
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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