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Implementation of wall functions with a constant shear boundary condition

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Old   February 27, 2012, 08:49
Arrow Implementation of wall functions with a constant shear boundary condition
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Brian
Join Date: Aug 2010
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Howdy,

I am trying to understand the implementation of wall functions in FLUENT when I specify a constant shear BC.

If I just set it to be a wall I understand what happens is:
1. Take cell centre velocity and calculate u_tau from the log-law relationship.
2. Calculate tau_w and apply this as a BC at the wall.
3. Solve the N-S Eqns in the cell to calculate the new cell centre value.

But what happens when I specify the wall shear stress. How does the log-law relationship get used in the calculation. Because all I can see is that you skip step one above, and just do two-three.

I understand there are lots of different details that I have ignored eg u_star vs u_plus and the exact log-law relationship etc, but I just want to get my head around the application.

Any input is much appreciated.
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