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.. only:: html

    .. note::
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        :ref:`Go to the end <sphx_glr_download_auto_how_to_example_turbulence.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_auto_how_to_example_turbulence.py:


Build an incompressible turbulence model
========================================

The :mod:`pybFoam.turbulence` submodule wraps OpenFOAM's incompressible
RAS / LES factory. This how-to reads the shipped ``pitzDaily`` case
(backward-facing step, k-epsilon RAS), constructs the turbulence
model from Python, and inspects its bound state — ``nut``, ``k``,
``epsilon``, ``correct()``, ``divDevReff()``.

Prerequisite: finished
:doc:`/auto_tutorials/example_01_dictionaries`.

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Clone the case
--------------

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.. code-block:: Python


    from pybFoam import clone_example

    case = clone_example("pitzDaily")








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Build mesh and read U
---------------------

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.. code-block:: Python


    from pybFoam import (
        Time,
        argList,
        createPhi,
        dictionary,
        fvMesh,
        volVectorField,
    )
    from pybFoam.meshing import generate_blockmesh

    time = Time(argList([str(case), "-case", str(case)]))
    generate_blockmesh(time, dictionary.read(str(case / "system" / "blockMeshDict")))
    mesh = fvMesh(time)

    U = volVectorField.read_field(mesh, "U")
    phi = createPhi(U)








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Construct the transport and turbulence models
---------------------------------------------
``singlePhaseTransportModel(U, phi)`` reads the Newtonian ``nu`` from
``constant/transportProperties``. ``incompressibleTurbulenceModel.New``
dispatches on ``simulationType`` and ``RASModel`` from
``turbulenceProperties`` to instantiate kEpsilon, kOmegaSST, etc.

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.. code-block:: Python


    from pybFoam.turbulence import (
        incompressibleTurbulenceModel,
        singlePhaseTransportModel,
    )

    transport = singlePhaseTransportModel(U, phi)
    model = incompressibleTurbulenceModel.New(U, phi, transport)








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Inspect the model
-----------------
Each accessor returns a ``tmp<volScalarField>``; call ``()`` to get
the underlying field, then ``["internalField"]`` for the NumPy view.

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.. code-block:: Python


    import numpy as np

    nut = np.asarray(model.nut()()["internalField"])
    k = np.asarray(model.k()()["internalField"])
    eps = np.asarray(model.epsilon()()["internalField"])

    print(f"nut       : shape={nut.shape}   min={nut.min():.3e}   max={nut.max():.3e}")
    print(f"k         : shape={k.shape}   min={k.min():.3e}   max={k.max():.3e}")
    print(f"epsilon   : shape={eps.shape}   min={eps.min():.3e}   max={eps.max():.3e}")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    nut       : shape=(12225,)   min=0.000e+00   max=0.000e+00
    k         : shape=(12225,)   min=3.750e-01   max=3.750e-01
    epsilon   : shape=(12225,)   min=1.486e+01   max=1.486e+01




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Update the eddy viscosity
-------------------------
``correct()`` is what a PISO/PIMPLE solver calls at the end of every
outer iteration. For k-epsilon it solves the k and epsilon transport
equations and recomputes ``nut = Cmu * k^2 / epsilon``.

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.. code-block:: Python


    model.correct()

    nut_after = np.asarray(model.nut()()["internalField"])
    print(f"nut after correct() : min={nut_after.min():.3e}   max={nut_after.max():.3e}")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    nut after correct() : min=1.938e-07   max=2.148e-03




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divDevReff in a momentum equation
---------------------------------
In a turbulent solver the laminar diffusion ``laplacian(nu, U)`` is
replaced by the model's stress divergence:

.. code-block:: python

   UEqn = fvVectorMatrix(fvm.ddt(U) + fvm.div(phi, U) + model.divDevReff(U))

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.. code-block:: Python


    UEqn_term = model.divDevReff(U)
    print(f"divDevReff term : {type(UEqn_term).__name__}")





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    divDevReff term : tmp_fvVectorMatrix




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See also
--------

- :doc:`example_modify_boundary_conditions` — change a patch field
  (e.g. inlet velocity) before constructing the turbulence model.
- :doc:`/auto_tutorials/example_04_run_and_sample` — drive a solver
  loop; add ``model.correct()`` inside it for a turbulent run.


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