[mjavrincon]

Dear community,

I have been trying to calculate the turbulence kinetic energy (TKE) of large eddy simulations (LES) for a while.
I have found that using the fieldAverage utility in OpenFOAM (the standard approach as I have seen) there is a big problem in the calculation of UPrime2Mean. Let me explain by having this code in controlDict:

functions
{
    fieldAverage
    {
        type            fieldAverage;
        libs            ("libfieldFunctionObjects.so");
        writeControl    writeTime;

        fields
        (
            U
            {
                mean        on;
                prime2Mean  on;
                base        time;
            }
        );
    }
}

The problem is that using directly this approach and starting the simulation, the UMean value used to calculate UPrime2Mean is not converged, thus yielding incorrect data unless a huge simulation is run to compensate for the iterations collected in which UMean is not converged.

As a solution, I have been trying to run first only UMean averaging, and when this field is converged, start the UPrime2Mean calculation, hoping that the convergence of the 2nd order statistics does not take that long.

However, I have not succeeded at doing so since the calculation of UPrime2Mean takes into account the number of time steps already used to calculate UMean and the UPrime2Mean field barely changes from the results obtained in the first iteration.

Have someone managed to fix or use a previous UMean field and use it to calculate UPrime2Mean?

Thank you in advance!

P.S. I have attached a figure of velocity probes in function of simulation time with the instantaneous values and 1st order statistics to show what I mean.