Ben-Malin/handyFunctionObjects

Place for me to keep useful OpenFOAM function objects when I come up with them, hopefully they can help you too.

handyFunctionObjects

Installation

Copy the directory somewhere, ensure the correct version of OpenFOAM is sourced, and run wmake

git clone https://github.com/Ben-Malin/handyFunctionObjects.git
cd handyFunctionObjects && wmake

This will compile a new library, libhandyFuncs.so, in your $FOAM_USER_LIBBIN directory.

To make use of the function objects, this library will need to be included in your controlDict, or passed to the postProcess application using the -lib flag

In controlDict:

libs
(
    "libhandyFuncs.so"
);

For postProcessing (note that objects which make use of a turbulence model require postProcess to be called through a solver):

simpleFoam -postProcess -latestTime -lib libhandyFuncs.so

Function Objects

SSTBlending

The $k\omega SST$ turbulence model uses a blending function, to apply the $k-\omega$ model in the near wall region, and the $k-\epsilon$ model in the freestream.
Sometimes, it might be interesting or useful to actually know where this blending takes place. This function object simply writes out the F1 blending function that is used to select the model coefficients.

Once installed, add the following to the functions section of your controlDict:

functions
{
    sstBlending
    {
        type            SSTBlending;
        libs            ("libhandyFuncs.so");
        executeControl  writeTime;
        writeControl    writeTime;
    }
}

And the blending field will be saved during your simulation. If you want to output the field for a simulation you've already run, you can use the simpleFoam -postProcess command as above

obLength

Function object to calculate the Obukhov length.
Only calculates at walls, doesn't bother to try calculating it throughout the field.

I've tried to keep it a bit more general than the functionObject in src/atmosphericModels
Enables use of arbitrary T field (so a potential/virtual temperature field can be used instead) and doesn't use the buoyant generation term for the calculation.

functions
{
    obLength
    {
        type            obLength;
        libs            ("libhandyFuncs.so");
        Tname           Tpot;
        executeControl  writeTime;
        writeControl    writeTime;
    }
}

The Obukhov length calculated as:

$$ L = \frac{-U_*^3 \cdot \theta_v}{\kappa \cdot g \cdot \overline{w' \theta_v '}} $$

The friction velocity $U_*$ is calculated as $\sqrt{\tau_{wall}}$, while the kinematic heat flux is calculated as:

$$ \overline{w'\theta_v'} = \frac{\alpha_t}{\rho} \cdot \frac{\partial \theta}{\partial z} $$