CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Cyclic Boundary Condition Errors?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 21, 2016, 15:37
Exclamation Cyclic Boundary Condition Bug/Error?
  #1
New Member
 
Join Date: Sep 2011
Posts: 3
Rep Power: 7
nyflyer is on a distinguished road
Hello all,

I'm trying to use the cyclic boundary condition to simulate periodicity, and the channel395 case has this implemented. However, looking at the channel395 case under post-processing, I notice that the boundary patches that are supposedly cyclic are not the same as you can tell by the pressure contours of p=0, and velocity magnitudes (see the attached screenshots.)

According to the boundary file in polyMesh (and the blockMeshDict) they should be cyclic, as below:
Code:
    inout1_half0
    {
        type            cyclic;
        inGroups        1(cyclic);
        nFaces          750;
        startFace       181700;
        matchTolerance  0.0001;
        transform       unknown;
        neighbourPatch  inout1_half1;
    }
    inout1_half1
    {
        type            cyclic;
        inGroups        1(cyclic);
        nFaces          750;
        startFace       182450;
        matchTolerance  0.0001;
        transform       unknown;
        neighbourPatch  inout1_half0;
    }
    inout2_half0
    {
        type            cyclic;
        inGroups        1(cyclic);
        nFaces          750;
        startFace       183200;
        matchTolerance  0.0001;
        transform       unknown;
        neighbourPatch  inout2_half1;
    }
    inout2_half1
    {
        type            cyclic;
        inGroups        1(cyclic);
        nFaces          750;
        startFace       183950;
        matchTolerance  0.0001;
        transform       unknown;
        neighbourPatch  inout2_half0;
    }
The boundaries on the pressure (0/p) as as follows:

Code:
 inout1_half0
    {
        type            cyclic;
    }
    inout2_half0
    {
        type            cyclic;
    }

    inout1_half1
    {
        type            cyclic;
    }
    inout2_half1
    {
        type            cyclic;
    }

That being said, is this is a bug in OpenFOAM or am I just not getting something right? From what I understand, the same solution should be on both cyclic patches (i.e. no equations are solved for this part of the matrix and the solution is just re-produced.)

What do you think is going on? Is this not the "periodic" boundary condition that I am expecting? If the cyclic BC is not the "periodic" boundary condition, then does OF have an implementation of the periodic boundary condition?

Moses
Attached Images
File Type: jpg inout1.jpg (42.5 KB, 16 views)
File Type: jpg inout2.jpg (46.3 KB, 13 views)
File Type: jpg inout_both.jpg (67.6 KB, 12 views)

Last edited by nyflyer; April 26, 2016 at 14:16.
nyflyer is offline   Reply With Quote

Old   April 21, 2016, 15:49
Default
  #2
New Member
 
Join Date: Sep 2011
Posts: 3
Rep Power: 7
nyflyer is on a distinguished road
The difference is even more pronounced when looking at the "sides" patches, as you can see from the picture that neither the pressure or the velocity contours match across the sides.


Note: I'm not talking about the discontinuity, but rather, the similarity (or differences in this case) between patches are that are facing each other.

Moses
Attached Images
File Type: jpg sides.jpg (61.3 KB, 9 views)
nyflyer is offline   Reply With Quote

Old   April 26, 2016, 14:14
Default
  #3
New Member
 
Join Date: Sep 2011
Posts: 3
Rep Power: 7
nyflyer is on a distinguished road
So I can't still figure this out if anyone has any insight. The channel395 case uses pimpleFOAM.

Is this a bug?

Moses
nyflyer is offline   Reply With Quote

Reply

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
Centrifugal fan j0hnny CFX 12 January 7, 2016 03:44
Mixing cyclic and wall boundary condition al_th OpenFOAM Pre-Processing 5 October 16, 2015 09:28
Radiation in semi-transparent media with surface-to-surface model? mpeppels CFX 10 June 16, 2015 15:48
Low Mixing time Problem Mavier CFX 5 April 29, 2013 00:00
About cyclic boundary condition mmkr825 OpenFOAM 0 December 14, 2012 02:36


All times are GMT -4. The time now is 12:13.