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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

Usage

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;

Sample output

Text reporting:

  • Coefficient data divided into total, pressure, viscous and porous contributions
forceCoeffs forceCoeffs1 write:
    Coefficient	Total	Pressure	Viscous	Internal
    Cd:	0.420059	0.406413	0.0136462	0
    Cd(f):	0.215934	0.208904	0.00703002	0
    Cd(r):	0.204125	0.197509	0.00661615	0
    Cl:	0.0530861	0.0530808	5.34317e-06	0
    Cl(f):	0.195825	0.189931	0.00589387	0
    Cl(r):	-0.142739	-0.13685	-0.00588852	0
    CmPitch:	0.169282	0.163391	0.00589119	0
    CmRoll:	0.00590429	0.00569735	0.000206938	0
    CmYaw:	0.000571337	0.000892135	-0.000320798	0
    Cs:	-0.0133976	-0.0131692	-0.000228412	0
    Cs(f):	-0.00612746	-0.00569246	-0.000435004	0
    Cs(r):	-0.00727014	-0.00747673	0.000206593	0

Stored properties

Reduced data

The following data are stored by the function object, and can be used by other function objects:

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

Fields

  • forceCoeff : force coefficients
  • momentCoeff : moment coefficients

Further information

Related:

Source code:

API:

Example usage: