Function Objects | CFD WITH A MISSION

In the case of Detached Eddy Simulations (DES), there are two regions in a computational domain that are treated in RANS-like and LES-like manners. The original Spalart-Allmaras DES model (DES97) formulation is based on the assumption that the wall-parallel grid spacing near the wall is in excess of the boundary-layer thickness \(\delta\) by a good margin so that the entire boundary layer can be handled by RANS [1].

Fig. 1 Natural DES grid in a boundary layer. Dotted line means velocity profile. \(\delta\) is the boundary-layer thickness [1].

Settings of DESModelRegions

In OpenFOAM, we can visually check these regions using the DESModelRegions function objects. It is also available in iconCFD.

functions

{

DESModelRegions1

{

type DESModelRegions;

functionObjectLibs ("libutilityFunctionObjects.so");

enabled true;

outputControl outputTime;

log true;

resultName DESRegions;

}

If log it true, the volume percent (%) of RANS and LES regions will be output to the screen:

DESModelRegions DESModelRegions1 output:

LES = 62.2455 % (volume)

RAS = 37.7545 % (volume)

Source Code

Directory:
OpenFOAM-v1606+/src/postProcessing/functionObjects/utilities/
DESModelRegions

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void Foam::DESModelRegions::execute()

{

if (active_)

{

const fvMesh& mesh = refCast<const fvMesh>(obr_);

if (log_) Info<< type() << " " << name_ << " output:" << nl;

volScalarField& DESModelRegions =

const_cast<volScalarField&>

(

mesh.lookupObject<volScalarField>(resultName_)

);

if (mesh.foundObject<DESModelBase>(turbulenceModel::propertiesName))

{

const DESModelBase& model =

mesh.lookupObject<DESModelBase>

(

turbulenceModel::propertiesName

);

DESModelRegions == model.LESRegion();

scalar prc =

gSum(DESModelRegions.internalField()*mesh.V())

/gSum(mesh.V())*100.0;

file() << obr_.time().value()

<< token::TAB << prc

<< token::TAB << 100.0 - prc

<< endl;

if (log_) Info

<< " LES = " << prc << " % (volume)" << nl

<< " RAS = " << 100.0 - prc << " % (volume)" << nl

<< endl;

}

else

{

if (log_) Info

<< " No DES turbulence model found in database" << nl

<< endl;

}

References

[1] P. R. Spalart, Detached-Eddy Simulation. Annual Review of Fluid Mechanics 41, 181-202, 2009.

OpenFOAM Version:
OpenFOAM-4.x

Settings of histogram

functions

{

temperatureHistogram

{

type histogram;

functionObjectLibs ("libfieldFunctionObjects.so");

outputControl outputTime;

// outputInterval 10;

field T;

nBins 10;

min 300;

max 310;

setFormat gnuplot;

}

Histogram

You can create a picture as shown below using Gnuplot with the input file generated by OpenFOAM. I replaced “with lines” with “with boxes” in the input command file to create this picture.

In the above picture, the first bin represents the following volume fraction:

\begin{align}
\frac{\sum_{celli}^{} \left( V_{celli}:\;300 \leq T_{celli} < 301\right)}{\sum_{celli}^{} \left( V_{celli}:\;min \leq T_{celli} < max\right)},
\end{align}

where \(V\) is the cell volume.

Category: Function Objects

Function Objects – DESModelRegions

Function Objects – histogram