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Old   October 5, 2016, 11:05
Smile CEL y+ calculation
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G Ionut
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Hi CFX experts,

I want to implement a new wall function in CFX-Pre using CEL language rather than Fortran, I found easier.

First I want to implement the standard wall function. So, I have the formula y+=\frac{u_{\tau}*\Delta y}{\nu}.
friction velocity: u_{\tau}=\sqrt{\frac{\tau_{w}}{\rho}}
kinematic viscosity: \nu
\Delta y=\Delta n/4 and "\Delta n is the distance between the first and second grid points off the wall." - Ansys help

I have the following problems:

1. How do I compute the Wall Shear Stress, \tau_{w} ? Until now I managed to computed it as \tau_{w}=ave(Wall Shear)@REGION:WALLS but I know that is wrong because the values for WSS are different over the geometry.

2. How do i compute \Delta n ?

3. In Ansys help they talk about some empirical formulas for the viscous sublayer, where do I find these empirical formulas ? All I know is that in the viscous sublayer u+=y+. "In the wall-function approach, the viscosity affected sublayer region is bridged by employing empirical formulas to provide near-wall boundary conditions for the mean flow and turbulence transport equations." - Ansys Help

I have done a k-\epsilon simulation with the built-in standard wall function from CFX to validate the wall function implementation.
I attached the CEL code too.

The geometry that I use is the Diffuser 1 from the article "Geometric sensitivity of three-dimensional separated by Erica M. Cherry"

Any help, tips, documentation etc. will be greatly appreciated. Thanks in advance for help.
Attached Files
File Type: txt MRV Diffuser1 3D KE SWF.txt (5.0 KB, 10 views)
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cel expression, wall shear stress, y plus

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