# 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 the controlDict.

• 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.

 1 2 3 4 5 6 7 8 9 type LOTWWallModel; RootFinder { type Newton; } Law { type Spalding; } 
• In your 0 directory, you should add a new volScalarField, h, see the Sampling section for details. For a quick start, set the value of h to uniform 0 at the wall, and use zeroGradient 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¶

• 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. the IntegratedReichardt 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!