# "Y plus" very important!!!

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 August 8, 2013, 15:28 "Y plus" very important!!! #1 New Member   Join Date: Jul 2013 Posts: 11 Rep Power: 6 Sponsored Links Hi! I need some information about the expected Y plus value for each turbulence model. Please help me!!!
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 August 8, 2013, 15:38 #2 Member   Ali.E Join Date: Sep 2010 Location: Lisboa Posts: 83 Rep Power: 8 hello, Y+ is very effective in the calculation, and the value may be 5-24 or 24-500 for RANS turbulence model. But it can be changeable for your simulation and results

 August 8, 2013, 15:57 #3 New Member   Join Date: Jul 2013 Posts: 11 Rep Power: 6 thank u for your response but i need a detailed information, such as how much acceptable y plus for realizable KE?

August 8, 2013, 18:31
#4
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Ali.E
Join Date: Sep 2010
Location: Lisboa
Posts: 83
Rep Power: 8
Actually, every boundary layer is divided into three parts: 1-sublayer 2-buffer layer 3-log law layer. All RANS turbulent models estimate viscosity and this viscosity is also included of molecular and/or turbulent ones. The importance of y+ lies in the fact that which part the center point of a mesh situates. Therefore, turbulent model estimates viscosity due to that part. In the buffer layer, we cannot have a good anticipation, as a consequence, it makes a recommend to avoid a y+ value in buffer layer. I enclose a picture to give the points

Quote:
 Originally Posted by Qube thank u for your response but i need a detailed information, such as how much acceptable y plus for realizable KE?
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August 10, 2013, 01:53
#5
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Saeed
Join Date: Jan 2013
Posts: 177
Rep Power: 6
Quote:
 Originally Posted by behest Actually, every boundary layer is divided into three parts: 1-sublayer 2-buffer layer 3-log law layer. All RANS turbulent models estimate viscosity and this viscosity is also included of molecular and/or turbulent ones. The importance of y+ lies in the fact that which part the center point of a mesh situates. Therefore, turbulent model estimates viscosity due to that part. In the buffer layer, we cannot have a good anticipation, as a consequence, it makes a recommend to avoid a y+ value in buffer layer. I enclose a picture to give the points
Please explain more. Thanks
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Last edited by flow_CH; August 10, 2013 at 08:56.

 August 10, 2013, 06:48 #6 New Member   Join Date: Jul 2013 Posts: 11 Rep Power: 6 my case study is a simplified car body and i want to use RKE or SST KW turbulence models. for more accurate results, how much should be y plus values?! which one is correct? 30< y+ <300 or y+ <5 ? Last edited by Qube; August 10, 2013 at 10:35.

August 10, 2013, 08:15
#7
Member

Ali.E
Join Date: Sep 2010
Location: Lisboa
Posts: 83
Rep Power: 8
Dear friend
The drag coefficient is depend to y+ value. I suggest to you to consider 30< y+ <300 initially; but if the results was not sufficient precision, then use another y+.
It has had an experience that the y+ <5 is achieved more accuracy

Quote:
 Originally Posted by Qube Dear saeed! my case study is a simplified car body and i want to use RKE or SST KW turbulence models. for more accurate results, how much should be y plus values?! which one is correct? 30< y+ <300 or y+ <5 ?

 August 10, 2013, 10:33 #8 New Member   Join Date: Jul 2013 Posts: 11 Rep Power: 6 thank you so much!

 Tags cfd, turbulence modeling, y plus

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