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yPlus value for a turbolent airfoil case

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Old   December 21, 2015, 12:15
Default yPlus value for a turbolent airfoil case
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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
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Old   December 21, 2015, 17:32
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Quote:
Originally Posted by Lorenzo92 View Post
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
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Old   December 22, 2015, 12:55
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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*?
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Old   December 22, 2015, 17:18
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Quote:
Originally Posted by Lorenzo92 View Post
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.


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Old   December 25, 2015, 04:23
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Ok Thanks for your advice anyway !!
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