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-   -   Automatic wall treatment in CFX (http://www.cfd-online.com/Forums/cfx/87484-automatic-wall-treatment-cfx.html)

Chander April 21, 2011 05:23

Automatic wall treatment in CFX
 
CFX uses automatic wall treatment for k-omega based models. According to CFX manual, when this option for wall treatment is selected, CFX automatically switches from between wall function approach and low Re approach depending upon the grid spacing near the wall.
Below what y+ (i.e. the non-dimensional distance of first mesh node from wall) does CFX switch from wall function approach to low Re approach for k-omega based models?

stumpy April 21, 2011 09:18

At y+=11.06, but I believe a smooth blend between the two approaches is used, so you won't get a sudden change at exactly that y+ value.

Far April 21, 2011 13:19

according to Menter above yplus 30 wall function and below yplus 2 low re formulation and between 2 and 30 blending of them

Chander April 25, 2011 07:22

Thank you stumpy and Far for the info. Is any detail of this blending available aywhere? I could not find in the help guides.

Far April 25, 2011 10:22

Quote:

Originally Posted by Chander (Post 304949)
Thank you stumpy and Far for the info. Is any detail of this blending available aywhere? I could not find in the help guides.

yes it is available in paper by Knopp (send me email address) in very much detail from basic to implementation into cfd code but little bit different than menters. For menter blending forumulae please to his 1998 and 2003 paper for scalable wall function and automatic wall treatment respectively. Very basic details are also given in CFD theory guide

Far April 25, 2011 10:24

please read cfd theory guide as CFX theory guide

Chander April 28, 2011 11:43

Thanks Far again for the info !. I have sent my email address to you by message. Please send me the paper by Knopp.
Thanks again !

Far April 30, 2011 16:09

Dear
Did you find the papers useful ?
Best Regards
Far

Chander May 3, 2011 12:32

Hi Far,

Many thanks for sending the papers. Yes, the papers are indeed very useful, especially the second one by Knopp. Its been a great help

Far May 3, 2011 13:19

Dear
You can also contact knopp through email. He is great person and will surely help you in understating the paper and topic in depth.

dogan May 22, 2013 09:39

Quote:

Originally Posted by stumpy (Post 304572)
At y+=11.06, but I believe a smooth blend between the two approaches is used, so you won't get a sudden change at exactly that y+ value.

Hi Stumpy,
can i ask where can i find a reference about the y+=11.06 value. is it for sure the limit value is 11.06, i need some references to write in my thesis.
thanks

Far May 22, 2013 11:39

have a look on this paper

http://num.math.uni-goettingen.de/ba...ings/knopp.pdf

http://www.os-cfd.ru/cfd_docs/wall_f..._functions.pdf

Quote:

Hi Stumpy, can i ask where can i find a reference about the y+=11.06 value. is it for sure the limit value is 11.06, i need some references to write in my thesis
This is intersection point of linear law and log law. That is applicable for the older wall treatment. For hybrid wall function (automatic wall treatment for kw based models) the limits are:

Y < 6 : integration to wall approach
Y+ 6-30 : blending of both approaches
Y+ > 30 : standard wall function


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