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

Using mapFields for dynamicMesh & bad results!!!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 3, 2013, 15:53
Default Using mapFields for dynamicMesh & bad results!!!
  #1
Senior Member
 
Sasan Ghomi
Join Date: Sep 2012
Location: Iran - Tehran
Posts: 185
Rep Power: 6
sasanghomi is on a distinguished road
Dear Friends ,

I am using dynamicMesh for engine simulation . I update the mesh manually and after remeshing I should map the latestTime of previous mesh on the new geometry (Actually new mesh ). The problem is that after each mapping I have got a big change in velocity field . Please take a look at the attached picture . In this picture you can see the variation of radial velocity versus time in a specific point in the engine . There are some big changes in the values of radial velocity (in the plot) . These big changes occur after each mapping (exactly) . Actually after each mapping velocity field is not coincide with previous time step in the previous mesh.
Please anybody help me for getting the reason of these big changes (rapid variation) . And How can I solve this problem ?

I appreciate any help from you
Thanks and best regards
Sasan.

P.S. I highlighted the big variations in the picture .
Attached Images
File Type: jpg radialvelocity.jpg (56.7 KB, 17 views)
sasanghomi is offline   Reply With Quote

Old   October 3, 2013, 16:45
Default
  #2
Senior Member
 
mturcios777's Avatar
 
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 727
Rep Power: 20
mturcios777 will become famous soon enough
Can you post a picture from ParaFoam with the velocity field from the old and new meshes? Also, are you mapping consistently or otherwise?
mturcios777 is offline   Reply With Quote

Old   October 3, 2013, 16:52
Default
  #3
Senior Member
 
Sasan Ghomi
Join Date: Sep 2012
Location: Iran - Tehran
Posts: 185
Rep Power: 6
sasanghomi is on a distinguished road
Dear Marco
Thank you very much for your reply
I used consistent mapping. I attached two pictures that they are after and before mapping . I think they are ok. But I don't know why there are some rapid variations in data that comes from swak4Foam.

Any Idea?

Best regards
Sasan

P.S. these pictures are not in the same time there is a little difference between time of them and difference in velocities in paraFoam comes from there
Attached Images
File Type: png befor map.png (35.8 KB, 18 views)
File Type: png aftermap.png (36.1 KB, 14 views)
sasanghomi is offline   Reply With Quote

Old   October 3, 2013, 16:58
Default
  #4
Senior Member
 
mturcios777's Avatar
 
Marco A. Turcios
Join Date: Mar 2009
Location: Vancouver, BC, Canada
Posts: 727
Rep Power: 20
mturcios777 will become famous soon enough
The interpolated fields look similar enough. I would check the discrete fields though, as interpolations smooths and tends to hide details that could be important.

Also, I'm not sure if its a problem with my web browser, but the engine seems to change diameter and the piston seems to move. It may be possible that the image is getting squished to fit as the aspect ratio may be different. In following with this, I would do a checkMesh on both meshes 1) to check the quality and 2) to compare the total mesh volume and dimensions.

Finally, how is swak4Foam calculating the radial velocity? Curious there may be something there worth noting.
mturcios777 is offline   Reply With Quote

Old   October 3, 2013, 17:06
Default
  #5
Senior Member
 
Sasan Ghomi
Join Date: Sep 2012
Location: Iran - Tehran
Posts: 185
Rep Power: 6
sasanghomi is on a distinguished road
the time of two pictures is a little different and that's why the piston has moved in the second picture.
About swak4Foam I should say that I wrote a function . I think this function is correct for any point on the axis of cylinder .And it can calculate radial velocity.

Take a look at this :

Code:
radialvelocity
    {
        type            swakExpression;
      expression     "(U.x*cos(teta))+(U.y*sin(teta))" ;
   variables "teta=atan((U.y)/(U.x));"    
functionObjectLibs ("libsampling.so");
         accumulations (
            average
        );
    //valueType    internalField;
         valueType set;
         setName   data;
        enabled         true;
        outputControl   outputTime;//timeStep;
        outputInterval  1;

     set {
            type cloud;
            axis z;
            points (

                (0 0.00000001 -0.005)

            );
        }
        
    }
Do you think is there any problem in this function?

P.S. the origin coordinate is in the center of cylinderHead.
sasanghomi 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
Problem: Very long "write" time (~2h-3h) for results and transient results Shawn_A CFX 16 April 12, 2016 20:49
Transient Run - Output "Time" in partial results? evcelica CFX 2 May 16, 2012 21:36
Lost Scenario Results..?? Fugacity Autodesk Simulation CFD 1 February 24, 2012 11:48
OpenFOAM - Validation of Results Ahmed OpenFOAM Running, Solving & CFD 9 June 22, 2011 18:59
wind tunnel results vs fluent pixie Main CFD Forum 1 August 20, 2009 08:02


All times are GMT -4. The time now is 20:07.