[losiola]

Hello guys ,


I am making a 2D Airfoil simulation Using pimpleFoam solver and the K Kl Omega transient turbulence Model . As i know, in a transient Simulation we have to pay attention to the Co (CFL) and it has to be less than 1 and we should be okk.



I run my simulation 2 times same mesh ,same boundary conditions and same evrything


the only difference is in the



maxCo in the controlDict.



for the first simulation i used maxCo 0.2
and for the second simulation i used maxCo 0.9


surprisingly i got different values of Cd and Cl



simulation1: Cd=0.0583 Cl =0.2747
simulation2: Cd= 0.01329 Cl=0.3424


Why is that ? and what is the reason behind this big diffrence in results?

this is the content for my control dict file:

application     pimpleFoam;

startFrom       latestTime;

startTime       0;

stopAt          endTime;

endTime         3;

deltaT          0.001;

writeControl    adjustableRunTime;

writeInterval   0.01;

purgeWrite      0;

writeFormat     binary;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;

adjustTimeStep  yes;

maxCo           0.2;


functions
{
 forces
    {
        type                forces;
        libs                ("libforces.so");
        writeControl        timeStep;
        writeInterval       10;
        patches             (wing);
        rho                 rhoInf;
        log                 true;
        rhoInf              1.204;
        CofR                (0 0 0);
    }
forceCoeffs1
{
    // Mandatory entries
    type            forceCoeffs;
    libs            ("libforces.so");
    patches         (wing);


    // Optional entries

    // Field names
    p               p;
    U               U;
    rho             rhoInf;
    rhoInf         1.204;
   // rhoInf            1.204;
    // 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 1 0);

    // Drag direction
    dragDir         (1 0 0);

    // Pitch axis
    pitchAxis       (0 0 1);

    // Freestream velocity magnitude [m/s]
    magUInf         10.679;

    // Reference length [m]
    lRef            1;

    // Reference area [m2]
    Aref            1;

    // Spatial data binning
    // - extents given by the bounds of the input geometry

}
}