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

Can initial condition makes the solution diverge?

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

Like Tree1Likes
  • 1 Post By kim4545

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 28, 2019, 15:02
Default Can initial condition makes the solution diverge?
  #1
New Member
 
Leegunho
Join Date: Jul 2019
Posts: 11
Rep Power: 4
kim4545 is on a distinguished road
Hello Foamer! I'm beginner of CFD.

I'm trying to simulate Supersonic nozzle with various Mach number.

The inlet pressure is 10bar, and outlet pressure is vacuum.

Inside of the nozzle is initially vacuum too.

Imagine the air is dumped into the vacuum tank from the pressure tank through the supersonic nozzle.

*The problem is that if i initialize the values to vacuum condition(P=0 or 1), solution diverges.

When i set the initial condition same as the inlet values(P=10bar), solution works.

But i want the processes of reaching steadystate from vacuum condtition, i want to set the initial values as vacuum.

I used Openfoam and Fluent, both of them diverged in vacuum initial condition. (SonicFoam, rhocentralFoam in openfoam)

If you have any ideas, please let me know.

Thanks for your attention. Im looking forward to your reply.


Attached Images
File Type: jpg Boundary_Initial.JPG (46.3 KB, 54 views)
Светлана likes this.
kim4545 is offline   Reply With Quote

Old   July 30, 2019, 12:46
Default
  #2
Senior Member
 
Peter Baskovich
Join Date: Jul 2014
Posts: 127
Rep Power: 8
pete20r2 is on a distinguished road
Yes, initial conditions can and often do cause divergence (usually in combination with other factors).
I would not set outlet to 0 as this is non-physical (bad start if you want real physics out).
Which pressure are you setting?
Can you share your solver output, it usually tells you what went wrong.
pete20r2 is offline   Reply With Quote

Old   July 31, 2019, 03:56
Default
  #3
Senior Member
 
Carlo_P
Join Date: May 2019
Location: Italy
Posts: 176
Rep Power: 5
Carlo_P is on a distinguished road
Hey Kim,
maybe the problem con be the relaxation factors.
In a case so difficult, you can have maybe some numerical issues.
At which iteration would diverge?
Can you try with very small relaxation factor?


Are you initializing all the domain with p=0?
This can be a problem, since not all the domain in the result is p=0.
If you want, you can try to initialize in different way, using TopoSetDict .
Cheers,
Carlo



p.s. can you post your BC files? I'm really interested in it.
Carlo_P 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
decompose dependent solution arionfard OpenFOAM 3 December 10, 2018 09:36
Foam::error::printStack after large bounding epsilon events StoneCFD727 OpenFOAM Running, Solving & CFD 1 January 1, 2018 17:04
Free surface issues with interDyMFoam for hydroturbine oumnion OpenFOAM Running, Solving & CFD 0 October 6, 2017 14:05
pressure in incompressible solvers e.g. simpleFoam chrizzl OpenFOAM Running, Solving & CFD 13 March 28, 2017 05:49
pimpleFoam: turbulence->correct(); is not executed when using residualControl hfs OpenFOAM Running, Solving & CFD 3 October 29, 2013 08:35


All times are GMT -4. The time now is 19:12.