How to update OpenFOAM numerical settings automatically at runtime

During an OpenFOAM simulation it is sometimes necessary to update a numerical scheme, for example, switching from first order to second order schemes to improve accuracy vs stability.

In order to perform these modifications automatically, we can add a function object to our controlDict, as shown in the following example, where after iteration 100 the fvSchemes is automatically updated:

functions
{
   fileUpdate1
   {
     type              timeActivatedFileUpdate;
     libs              ("libutilityFunctionObjects.so");
     writeControl      timeStep;
     writeInterval     1;
     fileToUpdate      "$FOAM_CASE/system/fvSchemes";
     timeVsFile
     (
         // start with first order
         (-1 "$FOAM_CASE/system/fvSchemes_1")
         // after 100 iterations use second order
         (100 "$FOAM_CASE/system/fvSchemes_2")  
     );
   }
}

In addition to the previous function object, we also need to make 2 copies of the “fvSchemes” file and rename them as “fvSchemes_1” and “fvSchemes_2”, both saved in the system directory.

In fvSchemes_1, divergence schemes are set to first order bounded “upwind” scheme:

divSchemes
{
   default         none;
   div(phi,U)      bounded Gauss upwind;
   div(phi,k)      bounded Gauss upwind;
   div(phi,omega)  bounded Gauss upwind;
   div((nuEff*dev(T(grad(U))))) Gauss linear;
   div(phi,nuTilda)      bounded Gauss upwind;  
}

And in fv_Schemes_2, divergence schemes are set to second order bounded “linearUpwind” scheme:

divSchemes
{
   default         none;
   div(phi,U)      bounded Gauss linearUpwind grad(U);
   div(phi,k)      bounded Gauss linearUpwind default;
   div(phi,omega)  bounded Gauss linearUpwind default;
   div((nuEff*dev(T(grad(U))))) Gauss linear;
   div(phi,nuTilda)      bounded Gauss linearUpwind default;    
}

In this way OpenFOAM when iteration 100 is reached, will use second order accuracy, so that when the number of grid points doubles, the discretization error will be reduced by a factor of 4.

お問い合わせ