[hooman.4028]

Any help please?!

[VSAndroid]

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.

Originally Posted by hooman.4028

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]

Originally Posted by VSAndroid

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]

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.

Originally Posted by hooman.4028

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]

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]

Originally Posted by VSAndroid

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]

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]

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]

It is very normal.

[cc2ley]

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]

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]

Thanks alot far!!
Really appreciate the advice since i am new to this
Guess that i am back to it then