# CEL y+ calculation

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October 5, 2016, 11:05
CEL y+ calculation
#1
New Member

G Ionut
Join Date: Sep 2016
Posts: 29
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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+=.
where:
friction velocity: =
kinematic viscosity:
= and " 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, ? Until now I managed to computed it as =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 ?

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- 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" http://www.sciencedirect.com/science...42727X08000131

Any help, tips, documentation etc. will be greatly appreciated. Thanks in advance for help.
Attached Files
 MRV Diffuser1 3D KE SWF.txt (5.0 KB, 10 views)

 Tags cel expression, wall shear stress, y plus