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forcesCoeffs - how to use relative pressure instead of absolute pressure

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Old   December 10, 2015, 11:51
Default forcesCoeffs - how to use relative pressure instead of absolute pressure
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Hi,
In controlDict I would like to use the relative pressure instead of the absolute pressure for the calculation of CD CL ecc.
I'm using the compressibile solver rhoSimplecFoam, and in the calculation of forces the absolute pressure is used.
I noticed the absolute pressure is also used in the calculation of force coefficents. I would like to use the relative pressure (so Prel =Pabs-Pref) in these calculations. Is it possible to specify Pref?
Thanks in advance,
WhiteW

Code:
 
       forces
        {
                type forces;
                functionObjectLibs ( "libforces.so" );
                outputControl timeStep;
                outputInterval 1;
                patches
                        (wall_body);
                pName p;
                UName U;
                rhoName rhoInf;
                log true;
                rhoInf 1.16;
                CofR (0 0 0);
                pitchAxis (0 -1 0);
        }

        forcesCoeffs
        {
                type forceCoeffs;
                functionObjectLibs ( "libforces.so" );
                outputControl timeStep;
                outputInterval 1;
                patches
                        ( wall_body );
                pName p;
                UName U;
                log true;
                rhoInf 1.16;
                CofR (0.98460 0 0.35195);         
                pitchAxis (0 -1 0);
                liftDir (0 0 1);
                dragDir (1 0 0);
                magUInf 44.85;
                lRef 0.3034;
                Aref 0.578;
        }
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Old   December 12, 2015, 07:26
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Hi, anyIdea?

I can calculate the corect forces with Paraview using the filters:
ExtractSurface
GenerateSurfaceNormal
Calculator
my reference pressure is 97956 Pa, so:
(p - 97956) * Normals
IntegrateVariables
I get the correct forces on the body.

If I use the formula (p) * Normals in the calculator, I get the output forces of OpenFoam(that uses the absolute pressure) .
Is there a way to do this operation inside openfoam?
Thanks,
WhiteW
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Old   December 22, 2015, 12:40
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Hi , is it possible to correct the evaluation of forces, using the relative pressure, only in the post-processing phase?
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