Force coefficients

The forceCoeffs function object generates aerodynamic force and moment coefficient data for surfaces and porous regions, with optional:

  • inclusion of porous drag
  • local co-ordinate system
  • data binning

Basic operation of the forceCoeffs function object comprises:

forceCoeffs1
{
    type            forceCoeffs;
    libs            ("libforces.so");
    patches         (<list of patch names>);
}

For more complete control, the full set of input entries includes:

forceCoeffs1
{
    // Mandatory entries
    type            forceCoeffs;
    libs            ("libforces.so");
    patches         (<list of patch names>);


    // Optional entries

    // Field names
    p               p;
    U               U;
    rho             rho;

    // Reference pressure [Pa]
    pRef            0;

    // Include porosity effects?
    porosity        no;

    // Store and write volume field representations of forces and moments
    writeFields     yes;

    // Centre of rotation for moment calculations
    CofR            (0 0 0);

    // Lift direction
    liftDir         (0 0 1);

    // Drag direction
    dragDir         (1 0 0);

    // Pitch axis
    pitchAxis       (0 1 0);

    // Freestream velocity magnitude [m/s]
    magUInf         30;

    // Reference length [m]
    lRef            1;

    // Reference area [m2]
    Aref            1.75;

    // Spatial data binning
    // - extents given by the bounds of the input geometry
    binData
    {
        nBin        20;
        direction   (1 0 0);
        cumulative  yes;
    }
}

Default behaviour assumes that the case is compressible. For incompressible cases, i.e. solved using the kinematic pressure:

\[ p_k = \frac{p}{\rho} \qquad [\mathrm{m}^2 \mathrm{s}^{-2}]\]

the rho entry can be used to set the freestream density:

rho         rhoInf;
rhoInf      100000;

Fields

  • force coefficients: forceCoeff
  • moment coefficients: momentCoeff

Storing of integrated values for further post-processing:

  • total moment coefficient: Cm
  • total drag coefficient: Cd
  • total lift coefficient: Cl
  • total front lift coefficient: Cl(f)
  • total rear lift coefficient: Cl(r)

Related:

Source code:

Example usage:

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