Quick start
Case setup
Assume that you’ve already set up a case for the classical wall-resolved LES. To convert it to WMLES you need to do the following:
Add
libWallModelledLES.so
to the loaded libraries in thecontrolDict
.Go into the
nut
file, and set up wall models as the boundary conditions at the walls. A minimalistic setup for a Spaling law-based algebraic wall model is given below.
1type LOTWWallModel;
2RootFinder
3{
4 type Newton;
5}
6Law
7{
8 type Spalding;
9}
In your
0
directory, you should add a new volScalarField,h
, see the Sampling section for details. For a quick start, set the value ofh
touniform 0
at the wall, and usezeroGradient
at all non-wall patch boundaries. This will lead to sampling from the wall adjacent-cell, which is very robust, but inaccurate.
The settings above are not optimal, but should get your case running. Of course, you should never run your WMLES on a wall-resolving mesh. Instead, we recommend using a meshing strategy presented in Grid construction.
Miscellaneous tips and troubleshooting
In regions where the TBL is attached, set
h
to be the distance to the second consecutive off-the-wall cell centre. In other regions, set it to 0, i.e. sample from the wall-adjacent cell.Use a mildly diffusive numerical scheme, e.g.
LUST
. Tips regarding what other schemes worked well are welcome :).The WALE model is a good first choice for SGS modelling. Don’t use implicit LES on a WMLES mesh.
If your simulation crashes because of the wall model (you can usually see that in the log), make sure you have a good initial condition.
If your simulation crashed anyway, use \(h = 0\), this is pretty much guaranteed to be stable.
Large values of \(h\) are known to sometimes lead to a crash, in particular, if the grid below \(h\) is refined.
If you use \(h = 0\), use an algebraic wall model in integral formulation, i.e. the
LOTWWallModel
with e.g. theIntegratedReichardt
law.
Publically available cases
There is a number of cases that use the library available on the web. These can serve as good examples on how to setup your simulation!
WMLES of channel and flat-plate TBL flow on unstructured grids. https://doi.org/10.6084/m9.figshare.12482438.v2
WMLES of channel flow and flow over a backward-facing step. https://doi.org/10.6084/m9.figshare.6790013.v1
WMLES of a flat-plate TBL using unstructured grids. https://doi.org/10.6084/m9.figshare.6061298.v2