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Calculating Lift and Drag Coefficients: All 0?

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Old   October 22, 2016, 13:03
Default Calculating Lift and Drag Coefficients: All 0?
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Peter
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Hi,

I'm trying to calculate lift and drag coefficients on the propeller test case (in pimpleDyMFoam). I seem to have gotten it working with no errors, but forces.dat just contains 0s. Here is the file:
Code:
# Forces     
# CofR       : (2.500000e-01 0.000000e+00 0.000000e+00)
# Time       forces(pressure viscous porous) moment(pressure viscous porous)
0.000333333  	((0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00)) ((0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00))
Here's the config file (or whatever it's called):
Code:
forces
{
    type                forces;
    functionObjectLibs  ("libforces.so");
    outputControl       timeStep;
    outputInterval      1;
     
    patches             ( “propellerStem1.*” );
    pName               p;
    UName               U;
    rhoName             rhoInf;
    log                 true;
     
    CofR                (0.25 0 0);
     
    rhoInf              1;
}
 
 
forceCoeffs
{
    type                forceCoeffs;
    functionObjectLibs  ( "libforces.so" );
    outputControl       timeStep;
    outputInterval      1;
 
    patches             ( “propellerStem1.*” );
    pName               p;
    UName               U;
    rhoName             rhoInf;
    log                 true;
     
    liftDir             (0 0 1);
    dragDir             (-1 0 0);
    CofR                (0.25 0 0);
    pitchAxis           (0 1 0);
     
    magUInf             2.00;
    rhoInf              1000;
    lRef                1;
    Aref                1;
}
What makes it all 0? Am I measuring from the wrong place? Should I somehow measure the whole propeller? How would I do that? Thanks for your help!
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Old   October 30, 2016, 12:51
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Quote:
Originally Posted by APCoding View Post
Hi,

I'm trying to calculate lift and drag coefficients on the propeller test case (in pimpleDyMFoam). I seem to have gotten it working with no errors, but forces.dat just contains 0s. Here is the file:
Code:
# Forces     
# CofR       : (2.500000e-01 0.000000e+00 0.000000e+00)
# Time       forces(pressure viscous porous) moment(pressure viscous porous)
0.000333333      ((0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00)) ((0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00) (0.000000e+00 0.000000e+00 0.000000e+00))
Here's the config file (or whatever it's called):
Code:
forces
{
    type                forces;
    functionObjectLibs  ("libforces.so");
    outputControl       timeStep;
    outputInterval      1;
     
    patches             ( “propellerStem1.*” );
    pName               p;
    UName               U;
    rhoName             rhoInf;
    log                 true;
     
    CofR                (0.25 0 0);
     
    rhoInf              1;
}
 
 
forceCoeffs
{
    type                forceCoeffs;
    functionObjectLibs  ( "libforces.so" );
    outputControl       timeStep;
    outputInterval      1;
 
    patches             ( “propellerStem1.*” );
    pName               p;
    UName               U;
    rhoName             rhoInf;
    log                 true;
     
    liftDir             (0 0 1);
    dragDir             (-1 0 0);
    CofR                (0.25 0 0);
    pitchAxis           (0 1 0);
     
    magUInf             2.00;
    rhoInf              1000;
    lRef                1;
    Aref                1;
}
What makes it all 0? Am I measuring from the wrong place? Should I somehow measure the whole propeller? How would I do that? Thanks for your help!
You need to stick with one density. In the quoted script, you defined rhoInf 1 and then you defined it again below but rhoInf 1000. Have you noticed that?

Best,
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