[CFD-Lover]

Hi All,

I am working on verifying the drag and lift coefficients using two different simulations (axisymmetric vs. 3D) of the flow over a C-D nozzle. Both simulations converged with four orders of magnitude. In both simulations, I have used the following force function;

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
forces
{
    type                forces;
    functionObjectLibs  ("libforces.so");
    outputControl       timeStep;
    outputInterval      1;
     
    patches             ( "CDNozzle.*" );
    pName               p;
    UName               U;
    rhoName             rhoInf;   // reference density
    log                 true;  
     
    CofR                (0 0 0);  // Center of rotation
     
    rhoInf              1;
}
 
 
forceCoeffs
{
    type                forceCoeffs;
    functionObjectLibs  ( "libforces.so" );
    outputControl       timeStep;
    outputInterval      1;
 
    patches             ( "CDNozzle.*" );
    pName               p;
    UName               U;
    rhoName             rhoInf;
    log                 true;
     
    liftDir             (0 1 0); // Direction of lift coefficient
    dragDir             (1 0 0); // Direction of drag coefficient
    CofR                (0 0 0);
    pitchAxis           (0 0 1); //Pitching moment axis
     
    magUInf             8; // Free stream velocity magnitude
    rhoInf              1;
    lRef                1;     //Reference lenght
    Aref                1;     // Reference area
}

// ************************************************************************* //

After converging, I have got the following values;
3D
Cd Cl
2.139615e-01 -1.042097e-03
Axisymmetric
Cd Cl
2.887599e-03 -3.213962e-03

In the axismmetric results for the drag, I did the following calculations;

Cd = 2.887599e-03*360/5 = 2.07907128e-01 (~3% error), where the value 5 is the wedge angle.

However, the lift coefficient doesn't seem to be right in the axismmetric results . I am not quite sure what could be the issue here? Anyone has done similar simulation could guide us?


Thanks for your time,