I am working on WMLES (wall Modelled LES) for which if I calculate my wall shear stress analytically and want to enforce it as a boundary condition at the wall patch, so that I do not need to resolve my near wall mesh rather give the wall shear stress as an input. One of the approach is defined by Schumann (1975) -(added an image below for the model formulation by Schumann) which I am trying to implement in OpenFOAM. My major question: Is there any method to define such a boundary condition of shear stress enforcement??
Because as far as the OpenFOAM user guide is concerned I could not find any such options. And the only way to define wall models is by changing the value of \nu_t.
Hi Nishidh Shailesh Naik Burye ,
If you have a constant, uniform, fixed shear stress field, OpenFOAM does have a "fixedShearStress" boundary which takes as input the vector value of \tau (assuming its constant over the entire boundary).
If you have anything more complicated (like a non-uniform shear stress field), you will unfortunately have to get your hands dirty coding a custom boundary condition. The easiest way would be to make a copy and modify the existing fixedShearStress boundary in OF. It imposes a Dirichlet boundary based on the velocity normal gradient field (from tau) and the cell-centred values of the velocity field from cells neighbouring the boundary. If you do follow this approach, it is important to just make sure you cancel out any velocity in the boundary normal direction, to make sure you don't accidentally, while converging, introduce inlet or outlet flow across the boundary.
Regards
In my case its mean shear stress (< \tau_w >) and apparently uniform over the patch. Thanks a lot Alfred Bogaers for the insight.
Alfred Bogaers, adding to my question, when we use such a condition of fixed shear stress for the wall, is it ment to be implemented when the grid size is resolved upto DNS? and in case of LES (where the grid is quire course) do we need to ensure that the first cell is in viscous sub layer, where Tau(total) = Tau_wall??
- Badges
- Science topic
- Similar topics
- Books