AOE 5984: Introduction to Parallel Computing Applications


OpenFOAM for CFD Applications

Lecture 3:  Data Analysis and Visualization


Professor Eric Paterson
Aerospace and Ocean Engineering, Virginia Tech
19 November 2013

Topics briefly discussed in Lecture 2

  • Introduction to OpenFOAM data analysis tools
  • Showed dictionary entries used by the sample utility for extracting sets and surfaces data from 4D fields
  • Showed example of plotting X-Y data (sets) with python+matplotlib
  • Showed example of visualizing surfaces rather than loading entire datasets
  • Emphasized  that data reconstruction should be avoided

Lecture 3:  Data Analysis & Visualization

  • Objectives
    • Highlight the difference between data analysis and visualization of OpenFOAM data
    • Discuss utilities and post-processing software for data analysis and visualization
  • Outcomes
    • Students will:
      • appreciate the importance of working with decomposed and remote data
      • understand that there are numerous OpenFOAM utilities for operating on data and computing derived data
      • learn about the power of using python and pyFoam
      • understand that client-server visualization is important for reducing data transfer and duplication 

    Data Analysis vs. Visualization

    • Data Analysis
      • Quantitative
      • Primary and derived variables
      • Integral variables, e.g., lift, drag, mass-flow rate
      • X-Y plots
      • Extraction of comparison metrics for verification and validation
    • Visualization
      • Qualitative
      • Primary and derived variables
      • Contour maps, streamlines, iso-surfaces, etc.
      • Animations

    OpenFOAM utilities

    • OpenFOAM has numerous pre-compiled post-processing utilities, which can be found in $FOAM_UTILITIES/postProcessing
    • Description of each can be found online at:  http://www.openfoam.org/docs/user/standard-utilities.php
    • Many of the utilities perform vector and tensor operations to compute derived variables, e.g., vorticity, Q, lambda2, shearStress, etc.

    velocityField postProcessing tools

    Post-processing velocity fields

    Co

    Calculates and writes the Courant number obtained from field phi as avolScalarField.

    enstrophy

    Calculates and writes the enstrophy of the velocity field U

    flowType

    Calculates and writes the flowType of velocity field U

    Lambda2

    Calculates and writes the second largest eigenvalue of the sum of the square of the symmetrical and anti-symmetrical parts of the velocity gradient tensor

    Mach

    Calculates and optionally writes the local Mach number from the velocity field U at each time

    Pe

    Calculates and writes the Pe number as a surfaceScalarField obtained from field phi

    Q

    Calculates and writes the second invariant of the velocity gradient tensor

    streamFunction

    Calculates and writes the stream function of velocity field U at each time

    uprime

    Calculates and writes the scalar field of uprime (∘ ----- 2k ∕3 \relax \special {t4ht=)

    vorticity

    Calculates and writes the vorticity of velocity field U

    Example:  Calculation of vorticity

    postProcessing/velocityField/vorticity/vorticity.C


        IOobject Uheader
    (
        "U",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ
    );

    if (Uheader.headerOk())
    {
        Info<< "    Reading U" << endl;
        volVectorField U(Uheader, mesh);

        Info<< "    Calculating vorticity" << endl;
        volVectorField vorticity
        (
            IOobject
            (
                "vorticity",
                runTime.timeName(),
                mesh,
                IOobject::NO_READ
            ),
            fvc::curl(U)
        );

        volScalarField magVorticity
        (
            IOobject
            (
                "magVorticity",
                runTime.timeName(),
                mesh,
                IOobject::NO_READ
            ),
            mag(vorticity)
        );

        Info<< "vorticity max/min : "
            << max(magVorticity).value() << " "
            << min(magVorticity).value() << endl;

        if (writeResults)
        {
            vorticity.write();
            magVorticity.write();
        }
    }
    else
    {
        Info<< "    No U" << endl;
    }

    wall postProcessing tools

    Example:  calculation of 

    wallShearStress

    void calcIncompressible
(
    const fvMesh& mesh,
    const Time& runTime,
    const volVectorField& U,
    volVectorField& wallShearStress
)
{
    #include "createPhi.H"

    singlePhaseTransportModel laminarTransport(U, phi);

    autoPtr<:rasmodel> model
    (
        incompressible::RASModel::New(U, phi, laminarTransport)
    );

    const volSymmTensorField Reff(model->devReff());

    forAll(wallShearStress.boundaryField(), patchI)
    {
        wallShearStress.boundaryField()[patchI] =
        (
           -mesh.Sf().boundaryField()[patchI]
           /mesh.magSf().boundaryField()[patchI]
        ) & Reff.boundaryField()[patchI];
    }
}

    where is the function devReff?

    Example:  kEpsilon.C











    tmp kEpsilon::devReff() const
{
    return tmp
    (
        new volSymmTensorField
        (
            IOobject
            (
                "devRhoReff",
                runTime_.timeName(),
                mesh_,
                IOobject::NO_READ,
                IOobject::NO_WRITE
            ),
           -nuEff()*dev(twoSymm(fvc::grad(U_)))
        )
    );
}

    python

    pyFoam

    http://openfoamwiki.net/index.php/Contrib_PyFoam

    pyFoam

    • This Python-library can be used to
      • analyze the logs produced by OpenFoam-solvers
      • execute OpenFoam-solvers and utilities and analyze their output simultaneously
      • manipulate the parameter files and the initial-conditions of a run in a non-destructive manner
      • plots the residuals of OpenFOAM solvers
    • Written by Bernhard Gschaider 

    pyFoam example

    http://pi.bgschaid.at/Hamburg/HamburgPresentedVersion.html#/

    Visualization

    • There are many very good visualization software packages
      • Paraview - free
      • Tecplot - Virginia Tech site license
      • Fieldview
      • Ensight
    • All of these packages natively read OpenFOAM data, plus numerous other formats
    • Making useful images requires experience and an eye for esthetics and art:   beware of chartjunk and colorful fluid dynamics

    Wind-turbine interaction:  Fieldview

    client-server visualization walkthrough

    How-to notes posted on Scholar

    next lecture:   meshing

    Captain Nemo's submarine, The Nautilus

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