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

Simulation RANS Explode

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 21, 2017, 11:40
Default Simulation RANS Explode
  #1
Member
 
Fredi Cenci
Join Date: Dec 2016
Posts: 38
Rep Power: 9
fredicenci is on a distinguished road
Hello all, I am trying to perform an URANS simulation (using PISO and k-omega SST) around a finite 3D cylinder and I would really appreciate any help.
Well, first of all I did a 2D simulation and worked pretty well, however when I go to the 3D domain the simulation blows, see the link with the files.





https://www.dropbox.com/…/134nlp…/AACQxNHwPovtqSx6tUYt6ylna…




I am pretty sure it is the non orthogonal faces in the end of the cylinder (checkMesh), but I can’t get rid of them ( If you take a look at the Cd in the top it goes way to high ) .. I tried to add correctors and change the schemes but it didn’t help…
Do you guys have any advice how to correct this faces or play with the correctors to get it right?
Thanks a lot!
fredicenci is offline   Reply With Quote

Old   May 23, 2017, 09:04
Default
  #2
Member
 
Joshua
Join Date: Dec 2016
Location: St. Louis, Missouri
Posts: 91
Rep Power: 9
Joshua14 is on a distinguished road
fredicenci,

Have you tried running a lower timeStep yet?

Joshua
Joshua14 is offline   Reply With Quote

Old   May 23, 2017, 09:52
Default
  #3
Member
 
Fredi Cenci
Join Date: Dec 2016
Posts: 38
Rep Power: 9
fredicenci is on a distinguished road
yeh, I've tried that and it doesn't help (i decreased by half). I have done the same simulation with a coarser mesh (with no non-orthogonal faces) and worked, however i couldn't get the vortex structures I was expecting, I guess it was because the mesh was way too coarse.

Thanks for your reply =)
fredicenci is offline   Reply With Quote

Old   May 23, 2017, 13:16
Default
  #4
Senior Member
 
piu58's Avatar
 
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15
piu58 is on a distinguished road
> (i decreased by half).

That may not be enough.

Start with the coarse mesh which works. The double the nodes and halve the time step. If that diverges halve the time step again until it runs.

It recommend the Courant control which some solvers offer. Even here, the usable Co may be very small for a given problem. It may be that you reach a value pretty below 1, may be even below 0.1.

The transformation of the mesh is often a very good choice. If you have (nearly) the same Co number in every part of the mesh the size of time step or usable Co number gets maximal for a given mesh resolution. If the relation of maximal to mean Co number exceeds 100 you should take this into account for sure.
__________________
Uwe Pilz
--
Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
piu58 is offline   Reply With Quote

Old   May 23, 2017, 13:29
Default
  #5
Member
 
Fredi Cenci
Join Date: Dec 2016
Posts: 38
Rep Power: 9
fredicenci is on a distinguished road
okay, i will try that.. I was thinking that the problem was with the mesh because the viscous layer is the same ( for the coarse mesh that worked and this one), therefore the problem could not be the Co because my Max Co would be the same on the cells near to the cylinder ... I guess this is not true...

I will reply with the results of decreasing the time-step ASAP.

Thanks for you reply! =}
fredicenci is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
setting up a simulation with multiple interactions phandy OpenFOAM Running, Solving & CFD 1 October 6, 2014 03:16
How is ANSYS CFX is related to RANS based Simulation Ramcad ANSYS 0 July 17, 2014 11:40
RANS simulation of Caradonna blade model deeps SU2 4 July 10, 2014 08:07
Discrete event simulation vs. fixed time (discrete time simulation) jenjon FLUENT 0 March 10, 2013 06:58
Quasi-2D mesh with gridgen for 2D RANS simulation L1011 OpenFOAM 0 February 26, 2011 12:53


All times are GMT -4. The time now is 08:36.