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-   -   How to abtain the correct y plus value. (https://www.cfd-online.com/Forums/fluent/50751-how-abtain-correct-y-plus-value.html)

hooman.4028 April 5, 2011 16:54
Any help please?!

VSAndroid April 8, 2011 08:27
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.


Quote:
Originally Posted by hooman.4028 (Post 302057)
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,

hooman.4028 April 8, 2011 11:23
Quote:
Originally Posted by VSAndroid (Post 302791)
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?

VSAndroid April 8, 2011 11:56
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.


Quote:
Originally Posted by hooman.4028 (Post 302812)
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?

basangaf January 12, 2012 20:22
Journal Article on Wall y+
 
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/

LuckyTran January 14, 2012 00:52
Quote:
Originally Posted by VSAndroid (Post 302818)
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.

bkm September 20, 2016 23:52
Y plus For Water Enclosed in Insulated Chamber and getting heat from Top of Chmaber
 
Hi is it really need to make boundary layer for Water Enclosed in Chamber and getting heat from top of the chamber. as pressure is atm. and air velocity inside is negligible at initial but as temp goes up there is increase in velocity.
So how do i calculate Y plus for it?

cc2ley February 3, 2018 09:01
I dont know how to deal with this
 
Hi, I am using a spallart allmaras model to run an external aerodynamic flow on a naca 0012 wing with 0 angle of attack. The Y+ values is between 0 and 8, which is not ideal. However, when i changed to the K-epsilon model, i get my wall y+ value to be between 0 and 1. However, the residual in K-epsilon and Spalart is vastly different. Has anyone here encounter something like this?

Far February 4, 2018 09:24
It is very normal.

cc2ley February 4, 2018 09:47
Hi far,
Thanks for the reply..
Since its normal, do i try to get both between 0 and 1? I am uncertain in what i should do

Far February 4, 2018 09:52
in both cases, the Y+ should be below 1 if you want to resolve the sublayer.

since both model will calculate the friction velocity differently and hence different Y+.

I would recommend to create Y+ value below 0.5 to get the Y+ below 1 for both models.

cc2ley February 4, 2018 09:59
Thanks alot far!!
Really appreciate the advice since i am new to this
Guess that i am back to it then


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