# slip or noslip U BC in openfoam?

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October 17, 2018, 11:53
some questions
#21
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meihuazhang
Join Date: Oct 2018
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Quote:
 Originally Posted by mAlletto you have an example in tutorials/incompressible/simpleFoam/pitzDaily. Actually since the Navier Stokes equations are second order in U you need two boundary condition for each component of the velocity. For the walls that means you need the velocity and the stresses at the wall. If you think on the discretization of the derivative of the stress tensor in the framework of a finite volume method you sum up the contributions of the stresses over the cell faces. At the wall you need to calculate the wall shear stress. If you do not have any wall function you multiply the velocity gradient with the viscosity to get the wall shear stress. If you have wall functions you multiply the turbulent viscosity nut with the velocity gradient. In order to get the correct wall shear stress in order to get the correct velocity at the cell centre close to the wall you need a wall function for nut. Hope this helps a bit. Michael
Hi Michael,
I am relative new to Openfoam. Now I would like to set wall shear stress (tauwall) boundary for LES and think on the discretization of the derivative of the stress tensor in the framework of a finite volume method. But I met some problems:
1 How to add 'tauwall' in the 0 file (because I will set wall shear stress boundary condition for LES). In the 0 file, I can see 'k' 'nut', but if I want to add 'tauwall', in which source file that I need to add or define ''tauwall'?

2 Do you know some cases or tutorials that use 'tauwall' as the boundary condition instead of 'nut'?

Thanks!
meihua

 October 17, 2018, 18:14 #22 Senior Member   Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 615 Rep Power: 16 There is a thread in les wall functios LES wall function and also a motorbike tutorial where wall functions for les are applied fede32 likes this.

 Tags head loss, kepsilon, pipe, slip, wall law

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