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 :code:`libWallModelledLES.so` to the loaded libraries in the
  :code:`controlDict`.
* Go into the :code:`nut` file, and set up wall models as the boundary
  conditions at the walls. A minimalistic setup for an explicit Spalding
  law-based algebraic wall model is given below.

.. code-block::
  :linenos:

  type           ExplicitWallModel;
  Law
  {
    type         Spalding;
  }

* In your :code:`0` directory, you should add a new volScalarField,
  :code:`hSampler`, see the :ref:`sampling` section for details. For a quick
  start, set the value of :code:`hSampler` to :code:`uniform 0` at the wall, and
  use :code:`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 :ref:`grid-construction`.

Miscellaneous tips
------------------

* In regions where the TBL is attached, set :code:`hSampler` 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. One can consider :code:`LUST` as a
  conservative option, but it is still very diffusive. On a good mesh, running
  with `linear` is a good option, as long as the simulation is stable.
* The WALE model is a good first choice for SGS modelling. Don't use implicit
  LES on a WMLES mesh.
* If you use :math:`h = 0`, use an algebraic wall model in integral formulation,
  i.e. the :code:`LOTWWallModel` with e.g. the :code:`IntegratedReichardt` law.
* Prefer explicit variations of wall models when they exist, e.g.
  :code:`ExplicitWallModel` subclasses. They are more robust and cannot fail
  inside a root-finder iteration.


Publicly 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 set up 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