CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Bugs

Possible problem with the size of simpleFilter?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   February 22, 2018, 05:03
Default Possible problem with the size of simpleFilter?
  #1
Senior Member
 
Kutalmis Bercin
Join Date: Aug 2012
Posts: 135
Rep Power: 7
HakikiCanakkaleli is on a distinguished road
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:

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
Quote:
(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:

Code:
    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 is offline   Reply With Quote

Old   February 24, 2018, 04:20
Default
  #2
Senior Member
 
Kutalmis Bercin
Join Date: Aug 2012
Posts: 135
Rep Power: 7
HakikiCanakkaleli is on a distinguished road
No SuperPerson? :]
HakikiCanakkaleli is offline   Reply With Quote

Old   March 1, 2018, 05:45
Default
  #3
Senior Member
 
Kutalmis Bercin
Join Date: Aug 2012
Posts: 135
Rep Power: 7
HakikiCanakkaleli is on a distinguished road
I reported this herein.
HakikiCanakkaleli is offline   Reply With Quote

Old   March 1, 2018, 06:53
Default
  #4
Senior Member
 
Kutalmis Bercin
Join Date: Aug 2012
Posts: 135
Rep Power: 7
HakikiCanakkaleli is on a distinguished road
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
HakikiCanakkaleli is offline   Reply With Quote

Reply

Tags
filtering, filters, large eddy simulation

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to write cellSet for different regions in constant/polyMesh/sets Struggle_Achieve OpenFOAM Meshing & Mesh Conversion 2 March 9, 2017 02:46
OF 1.6 | Ubuntu 9.10 (64bit) | GLIBCXX_3.4.11 not found piprus OpenFOAM Installation 22 February 25, 2010 13:43
Problems in compiling paraview in Suse 10.3 platform chiven OpenFOAM Installation 3 December 1, 2009 07:21
Need help with the error cfdproject OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 0 April 14, 2009 15:45
Phase locked average in run time panara OpenFOAM 2 February 20, 2008 14:37


All times are GMT -4. The time now is 10:00.