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How to abtain the correct y plus value.

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Old   April 5, 2011, 16:54
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Hooman
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Any help please?!
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Old   April 8, 2011, 08:27
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What K-E model are you using? I have found that Realiazable is the best. Also what sort of wall treatment are you using? If it's standard wall funtion you want to aim for y+ values of greater than 30. If it's enhanced wall function you need your y+ to be less than 1, which means you will need a very fine mesh at the wall.


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Dear all,

I am modelling flow over an ellipse using k=e model. I have a problem with my yplus magnitude.....my yplus magnitude near my wall is around 500 and it decreases by going far from the wall and reaches to zero in the first node. first i don't know why it doesn't start from zero and then goes to higher magnitudes? second, why i have such a high magnitude of yplus?my speed is 40 m/s and my meshes are really fined. also i defined boundary layer meshes in gambit.

Thanks,
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Old   April 8, 2011, 11:23
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Quote:
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What K-E model are you using? I have found that Realiazable is the best. Also what sort of wall treatment are you using? If it's standard wall funtion you want to aim for y+ values of greater than 30. If it's enhanced wall function you need your y+ to be less than 1, which means you will need a very fine mesh at the wall.
Thank you so much for your quick answer. I'm using standard k-e. I have another problem, I don't know why i am getting yplus values in the reverse order.i mean that i have the maximum yplus near my wall and zero value on the first node. i think there is sth wrong with the direction of my boundary layer meshes.isn't it?
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Old   April 8, 2011, 11:56
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Your Y+ values should be corresponding to your wall ONLY. If you are using Standard wall function for KE - Aim for Wall Y+ values between 30 and 150 at the wall.


Search for an article "Wall Y+ Strategy for dealing with wall bounded turbulent flows" by Salim M. Salim and S.C. Cheah - It is a very good paper.

Email me on vh00011@surrey.ac.uk - if you can't find the paper and I will send it you.


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Thank you so much for your quick answer. I'm using standard k-e. I have another problem, I don't know why i am getting yplus values in the reverse order.i mean that i have the maximum yplus near my wall and zero value on the first node. i think there is sth wrong with the direction of my boundary layer meshes.isn't it?
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Old   January 12, 2012, 21:22
Default Journal Article on Wall y+
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And the corresponding journal paper is titled "Wall y+ approach for dealing with turbulent flows over a wall mounted cube" published in "Progress in Computational Fluid Dynamics" by Inderscience.
http://inderscience.metapress.com/co...0284130n05742/
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Old   January 14, 2012, 01:52
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Quote:
Originally Posted by VSAndroid View Post
Your Y+ values should be corresponding to your wall ONLY. If you are using Standard wall function for KE - Aim for Wall Y+ values between 30 and 150 at the wall.


Search for an article "Wall Y+ Strategy for dealing with wall bounded turbulent flows" by Salim M. Salim and S.C. Cheah - It is a very good paper.

Email me on vh00011@surrey.ac.uk - if you can't find the paper and I will send it you.
Salim's paper is a very good paper (especially for beginners) for understanding wall modeling approaches and wall y+. I also highly recommend it's read.
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