Info<< "Reading combustion properties\n" << endl;

IOdictionary engineGeometry
(
    IOobject
    (
        "engineGeometry",
        runTime.constant(),
        mesh,
        IOobject::MUST_READ,
        IOobject::NO_WRITE
    )
);

vector swirlAxis
(
    engineGeometry.lookup("swirlAxis")
);

vector swirlCenter
(
    engineGeometry.lookup("swirlCenter")
);

dimensionedScalar swirlRPMRatio
(
    engineGeometry.lookup("swirlRPMRatio")
);

dimensionedScalar swirlProfile
(
    engineGeometry.lookup("swirlProfile")
);

dimensionedScalar bore
(
    engineGeometry.lookup("bore")
);

dimensionedScalar rpm
(
    engineGeometry.lookup("rpm")
);


Info<< "Reading field U\n" << endl;
volVectorField U
(
    IOobject
    (
        "U",
        runTime.timeName(),
        mesh,
        IOobject::MUST_READ,
        IOobject::AUTO_WRITE
    ),
    mesh
);

vector zT = swirlAxis;
vector yT = vector(0, zT.z(), -zT.y());
vector xT = vector(zT.y()*zT.y() + zT.z()*zT.z(), -zT.x()*zT.y(), -zT.x()*zT.z());

// if swirl is around (1, 0, 0) we have to find another transformation
if (mag(yT) < SMALL)
{
    yT = vector(zT.y(), -zT.x(), 0);
    xT = vector(-zT.x()*zT.z(), -zT.y()*zT.z(), zT.x()*zT.x() + zT.y()*zT.y());
}

//swirlAxis doesn't have to be of unit length.
xT /= mag(xT);
yT /= mag(yT);
zT /= mag(zT);