[alex-bishop]

when i use turbogrid to creat mesh i do not know how to decrease the y+ value around blade. the value is in the passage tab. i want some help from you.
i appreciate it very much.

[Ahmed Saeed Mansour]

What is the required y+ that you have to use?

[alex-bishop]

Originally Posted by Ahmed Saeed Mansour

What is the required y+ that you have to use?

i think 20-300. i am studying turbine. i also want to know how to choose reasonable Y+ range. can you give me some advices?

[Ahmed Saeed Mansour]

Okay, the idea behind y+ is to calculate the first layer height"the first cell near the wall or the airfoil surface" to capture a specific physical phenomena that requires high resolution cells"fine grid"...One of these phenomenas is the boundary layer especially near the airfoil's surface....So, you have to know the recommended y+ for your simulation and you can get it from google or any CFD reference that covers the y+ illustration and how to calculate the first layer height for internal and external flow..They use some basic and empirical equations...So, the 1st thing now is to tell me the required y+ then you can substitute it the equations to get the 1st cell height then we can enter the next stage...
Check out these
y+:
http://www.computationalfluiddynamic...t-cell-height/

The following link is about a CFD course..The Dr. illustrated the idea of y+ in a video but I don't remember the number of it so try to find it out.
https://www.youtube.com/watch?v=WPnpqsAkoR8

Mesh independence
http://www.computationalfluiddynamic...pendent-study/

My tutorial on youtube

https://youtu.be/2951JXtWJ4w

Thanks

[alex-bishop]

thank you very much. it is really helpful. i also want to ask a question about the wall function. does it mean i can not get detail about flow status in laminar sublayer of boundary layer when i use such as k-e model with wall function ?

[alex-bishop]

and i want to know that why y+ can not be too small ?

[Ahmed Saeed Mansour]

Dear Alex, study these couple of pages in Ansys Fluent user and theory guide..
Theory guide "page 112-131"

http://www.mediafire.com/file/6ww6sn...eory+Guide.pdf

And user guide " Chapter 12 k-e model"

http://www.mediafire.com/file/3q0hs3...sers+Guide.pdf

Y+ is set to lower than 1 if the physical phenomena requires a very high fine mesh near the surface such as the surface of the airfoil...to study the sublayer of the boundary layer.

After that if you have questions ...I am ready...Keep going

[Ahmed Saeed Mansour]

And at some simulations the too small y+ may cause solution instabilities so we do not use too low values of y+

[alex-bishop]

Originally Posted by Ahmed Saeed Mansour

And at some simulations the too small y+ may cause solution instabilities so we do not use too low values of y+

in this picture the stadard wall function was used with k-e model. y+=75. we can see that we get the flow detail in logarithmic layer but we can not get detail about buffer layer and laminar layer. so i want to know that if we can not get flow detail in laminar layer when we use wall function?

[Ahmed Saeed Mansour]

You can read about that in page 122 in the theory guide...I think if you wanna get the viscous sublayer you have to make y+ equal to 1 and use enhanced wall treatment in k-e but this will require a very fine grid near the wall.

[alex-bishop]

Originally Posted by Ahmed Saeed Mansour

You can read about that in page 122 in the theory guide...I think if you wanna get the viscous sublayer you have to make y+ equal to 1 and use enhanced wall treatment in k-e but this will require a very fine grid near the wall.

thank you very much.

[Ahmed Saeed Mansour]

Not at all dear Alex...Keep goin'