[jlb001]

I am reading the fluent help manual since one day and I don't manage to find a precise answer on the resolution of the boundary layer for FLUENT.

I am using Enhanced wall treatment :
- for KE , I understood, if the mesh is suffisently small (Y+=1) then the 2 layers model will be used. If the mesh is coarse a wall function using :
Kader [168] + White and Cristoph [418] and Huang et al. [147] will be used.
Is it ok ?
- But for kw-SST it become really really unclear :
(chapter 4.4.4. Wall Boundary Conditions for Kw-SST)
"This means that all boundary conditions for wall-function meshes will correspond to the wall function approach, while for the fine meshes, the appropriate low-Reynolds-number boundary conditions will be applied" (this is all right ;-))
and after :Analytical solutions can be given for both the laminar sublayer (eq : 4–118) and the logarithmic region (4–119).
Therefore, a wall treatment can be defined for the w equation, which switches automatically from the viscous sublayer formulation to the wall function, depending on the grid. This blending ..."
Are these equation used for a modeling the boundary layer or are they wall functions ?
I am quite deasapointed because in Chapter :4.13.5.( Enhanced Wall Treatment ω-Equation (EWT-ω)) it is stated :
"the Kw-equation can be integrated through the viscous sublayer without the need for a two-layer approach. This feature can be utilized for a y* -insensitive wall treatment by blending the viscous sublayer formulation and the logarithmic layer formulation based on y*,This formulation is the default for all Kw equation based models."
And finaly in 4.13.4. (Enhanced Wall Treatment ε-Equation (EWT-ε))
"Please note that an alternative blending compared to the Kader-blending is used for the improved near wall treatment for turbulence models based on the w equation, which is the new default near wall treatment."

I do not understand what is the wall function and what are the equations used for modeling (or blending ...) the complete BL ?

If somebody get the point ...

Thanks in Advance


JB

[jlb001]

No idea ???

[cfd_newbie]

Originally Posted by jlb001

I am reading the fluent help manual since one day and I don't manage to find a precise answer on the resolution of the boundary layer for FLUENT.

I am using Enhanced wall treatment :
- for KE , I understood, if the mesh is suffisently small (Y+=1) then the 2 layers model will be used. If the mesh is coarse a wall function using :
Kader [168] + White and Cristoph [418] and Huang et al. [147] will be used.
Is it ok ?
- But for kw-SST it become really really unclear :
(chapter 4.4.4. Wall Boundary Conditions for Kw-SST)
"This means that all boundary conditions for wall-function meshes will correspond to the wall function approach, while for the fine meshes, the appropriate low-Reynolds-number boundary conditions will be applied" (this is all right ;-))
and after :Analytical solutions can be given for both the laminar sublayer (eq : 4–118) and the logarithmic region (4–119).
Therefore, a wall treatment can be defined for the w equation, which switches automatically from the viscous sublayer formulation to the wall function, depending on the grid. This blending ..."
Are these equation used for a modeling the boundary layer or are they wall functions ?
I am quite deasapointed because in Chapter :4.13.5.( Enhanced Wall Treatment ω-Equation (EWT-ω)) it is stated :
"the Kw-equation can be integrated through the viscous sublayer without the need for a two-layer approach. This feature can be utilized for a y* -insensitive wall treatment by blending the viscous sublayer formulation and the logarithmic layer formulation based on y*,This formulation is the default for all Kw equation based models."
And finaly in 4.13.4. (Enhanced Wall Treatment ε-Equation (EWT-ε))
"Please note that an alternative blending compared to the Kader-blending is used for the improved near wall treatment for turbulence models based on the w equation, which is the new default near wall treatment."

I do not understand what is the wall function and what are the equations used for modeling (or blending ...) the complete BL ?

If somebody get the point ...

Thanks in Advance


JB

Can you please simplify as to what is your question. Don't quote FLUENT manual help. Just post your question.

[jlb001]

Dear cfd_newbie,

To be simple, my question is just about how Fluent is dealing with wall treatment of Kw-SST models.
When Fluent is using a wall function (if the mesh is not fine enought) what are the equations ?
When FLUENT is using a wall treatment (by modelling), does it solve the NS equations until the wall or is it using a blending function ?

Thanks in advance

JB