CFD Online Discussion Forums - airfoil analysis need help!!!

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airfoil analysis need help!!!

Hi Foamers!
I'm trying to do some simple 2D airfoil analysis.
in doing some tests on the classic NACA 0012 airfoil. has anyone done more or less the same thing? can anyone give me some hints?

I'm using simpleFoam as a solver (k-e turbulence model with the constants values of the simpleFoam tutorial), because icoFoam and turbFoam start with fireworks after few iterations...

my simulations need more or less 1700 iterations to converge to a steady state (looking to U and p distributions), is it reasonable?

I haven't figured out how to obtain forces on the airfoil... does anyone know how to do it?

I'm afraid I'm not using the correct turbulence model or the the wrong values of the k-e constants...

every hint is very useful!

thanks a lot

DLC

Quote:

Originally Posted by DLC (Post 253742)

Hi DLC,

getting force values is a matter of postprocessing.
You might want to checkout paraFoam for this or if you have a license you might want to use ensight (or similar).
Getting forces is then straight forward and well documented in the video-posts from ensight-page.
If you use paraFoam you might want to buy the manual, otherwise you will have fun guessing...

regards

HI DLC
I have previously done a case on Naca 0012 airfoil with Fluent, but my results was looking wrong. how was your results? did you get correct results?

well, actually I cant tell yet if my results are correct... I tested a lot of different configurations, (BC and turbulence models) and managed to find a settings that actually converge to a stationary situation (looking to the p andU distribution), bun I haven't discovered yet how to calculate forces, thereore Cl, Cd, Cm... how did you manage to obtain these? a help on how to calculate forces would permit me to give results even tonight...
If you want to send me your test case, I can have a look to differences..

let me know

DLC

I'm not an expert, I'm a beginner, so use the search tool in the forum to check my suggestions. There is also a 2D airfoil case in tutorials/incompressible/simpleFoam. The turbulence model depends on your Reynolds number. If you have a high Re, I think you can use $\kappa-\epsilon$ , $\kappa-\omega SST$ or Spalart-Allmaras model. Otherwise you must use a low Re model.
I think 1000 iterations is enough, you can check your residuals.
In order to calculate lift and drag coefficients, you can include in controlDict code lines as:

Code:

functions

{

    forces

    {

        type        forces;

        functionObjectLibs ( "libforces.so" );  // lib to load

        outputControl timeStep;

        outputInterval 1;

        patches

        (

            wall  // change to your patch name

        );

        // name of fields

        pName       p;

        UName       U;

        log         true; // dump to file

        rhoInf      1025;

        CofR        ( 0 0 0 );

    }

    forcesCoeffs

    {

        type        forceCoeffs;

        functionObjectLibs ( "libforces.so" );  // lib to load

        outputControl timeStep;

        outputInterval 1;

        patches

        (

            wall  // change to your patch name

        );

        // name of fields

        pName       p;

        UName       U;

        log         true; // dump to file

        rhoInf      1025;

        CofR        ( 0 0 0 );

        liftDir     ( 0 1 0 );

        dragDir     ( 1 0 0 );

        pitchAxis   ( 0 0 0 );

        magUInf     7.30;

        lRef        0.305;

        Aref        0.001525;

    }

}



// Definition of terms:

// rhoInf - reference density

// CofR - Centre of rotation

// dragDir - Direction of drag coefficient

// liftDir - Direction of lift coefficient

// pitchAxis - Pitching moment axis

// magUinf - free stream velocity magnitude

// lRef - reference length

// Aref - reference area