[HakikiCanakkaleli]

Hi,

Please consider a large eddy simulation in which dynamicLagrangian SGS model is used with the test filter simpleFilter. Then please consider the support of the first filter is Delta, assuming cubeRootVolDelta in use. Conventionally, the support of the test filter, simpleFilter herein, is assumed twice the first filter, i.e. 2Delta.

Let's further assume a 3-node grid as follows:

|--o--|--o--|--o--|

where |s are faces, and os are nodes. Let's say the nodes store the following values of an arbitrary variable: 10 (Neighbour-Left), 20 (Owner), 10 (Neighbour-Right).

Please assume all other settings are default.

The alleged problem is, IMHO, the averaging radius of the test filter, simpleFilter, seems to be different from 2Delta. Below shows the relevant part of the code:

Foam::tmp<Foam::volVectorField> Foam::simpleFilter::operator()
(
    const tmp<volVectorField>& unFilteredField
) const
{
    correctBoundaryConditions(unFilteredField);

    tmp<volVectorField> filteredField = fvc::surfaceSum
    (
        mesh().magSf()*fvc::interpolate(unFilteredField)
    )/fvc::surfaceSum(mesh().magSf());

    unFilteredField.clear();

    return filteredField;
}

Therein, the neighbours and owner are interpolated on the owner cell's faces. Considering our example, this results in 15 (Owner-Face-Left) and 15 (Owner-Face-Right). Then, the face values are averaged to obtain the test filter value for the owner, leading to 15.

However, IMHO, 2Delta should result in

(10+20+10)/3 = 13.3.

2Delta was incorporated into the dynamicLagrangian as can be seen from this, where M was correctly derived with the assumption of 2Delta:

    volSymmTensorField M
    (
        2.0*sqr(this->delta())*(filter_(magS*S) - 4.0*magSf*Sf)
    );

The alleged problem is above that filter_() operation's support is not equal to 2Delta, yet a slightly different value despite the relevant equations seem to be derived with 2Delta.

The same question was discussed in there with no conclusion.

Kind regards,

[HakikiCanakkaleli]

No SuperPerson? :]

[HakikiCanakkaleli]

I reported this herein.

[HakikiCanakkaleli]

It seems this observation is correct, but its prospective effects were presumed to be insignificant to LES solutions (I also agree with this presumption for the moment - tests are needed to prove the opposite): https://bugs.openfoam.org/view.php?id=2865