# yPlus value for a turbolent airfoil case

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 December 21, 2015, 12:15 yPlus value for a turbolent airfoil case #1 Member   Lorenzo Join Date: Oct 2015 Location: Milan Posts: 46 Rep Power: 3 Hi, I runned a case of an airfoil immersed in an incompressible flow with an angle of attack of 4 degree. My turbolence model is Spalart-Allmaras, my solver is simpleFoam. At the end of the running I wanted to visualize the y+ values on the airfoil by running the application yPlusRas . My questions are: 1) was it correct to use yPlusRas for displaying maximum y+ on the airfoil?( so far I know y+ is the height of the first cell center on the surface) 2) My result of maximum y+ (by running yPlusRas) on the airfoil is 478, does this make sense if the case Re was 6000000? Personally I thought I had to create a finer grid around the airfoil otherwise I cannot catch sufficiently good the boundary layer with a so high y+. Thanks

December 21, 2015, 17:32
#2
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shereez
Join Date: Jan 2014
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Quote:
 Originally Posted by Lorenzo92 Hi, I runned a case of an airfoil immersed in an incompressible flow with an angle of attack of 4 degree. My turbolence model is Spalart-Allmaras, my solver is simpleFoam. At the end of the running I wanted to visualize the y+ values on the airfoil by running the application yPlusRas . My questions are: 1) was it correct to use yPlusRas for displaying maximum y+ on the airfoil?( so far I know y+ is the height of the first cell center on the surface) 2) My result of maximum y+ (by running yPlusRas) on the airfoil is 478, does this make sense if the case Re was 6000000? Personally I thought I had to create a finer grid around the airfoil otherwise I cannot catch sufficiently good the boundary layer with a so high y+. Thanks
I have read in this forum that OpenFOAM yPlusRas is actually YStar and not actualy Y plus. With in my knowledge if you are using wall functions - Y plus has to be between 30 to 100. If you are resolving wall boundary then Y+ should be strictly 1 or lower, although some people use a value below 5 too. May be it will be a good idea to read the law of the wall on wiki

Regards
Shereez

 December 22, 2015, 12:55 #3 Member   Lorenzo Join Date: Oct 2015 Location: Milan Posts: 46 Rep Power: 3 So the result of running yPlusRAS is the maximum , the minimum and the averaged value of the height of the first cell center in y+ dimensionless unit. Is this the meaning of y*?

December 22, 2015, 17:18
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shereez
Join Date: Jan 2014
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Quote:
 Originally Posted by Lorenzo92 So the result of running yPlusRAS is the maximum , the minimum and the averaged value of the height of the first cell center in y+ dimensionless unit. Is this the meaning of y*?
Y Plus is the First cell height normal to the wall. Y star is the length along the first cell ( parallell to the flow) I guess. I advise you to read on it, again.

Sorry for not being a great help.

Shereez

 December 25, 2015, 04:23 #5 Member   Lorenzo Join Date: Oct 2015 Location: Milan Posts: 46 Rep Power: 3 Ok Thanks for your advice anyway !!

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