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

Fatal over flow in solver

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 4, 2002, 12:47
Default Fatal over flow in solver
  #1
Nandu
Guest
 
Posts: n/a
Hi,

I'm modelling supersonic jet flows into still air. I have managed to get convergence of M = 1.41 (ideally expanded) flow into still air using a local timestep factor for the solver control in CFX 5.5

When i change the inlet pressure conditions in the results file from the previous simulation so that i can get an underexpanded or over expanded jet, the solver crashes with the error being a 'fatal over flow in the liner solver'.

This error also comes when i use a new definition file with the old results file as an intial guess. Changing the local time step factor has not helped. The failure of the simulation is the at the 1st timestep. Any help to rectify this situation is most appreciated.

regards N Menon
  Reply With Quote

Old   September 4, 2002, 15:56
Default Re: Fatal over flow in solver
  #2
Robin
Guest
 
Posts: n/a
Hi Menon,

Your change in the boundary condition is probably too dramatic. Try making a series of small changes, or starting from scratch with the new condition.

Furthermore, you should limit the use of a local timestep factor to getting initial convergence for your simulation. You should switch to a Physical or Automatic timescale and run to convergence before interpreting the results.

Regards, Robin
  Reply With Quote

Old   September 5, 2002, 07:43
Default Re: Fatal over flow in solver
  #3
Nandu
Guest
 
Posts: n/a
Well heres the scenario. I ran the simulation for a M=1.41 jet (nozzle exit pressure equals ambient pressure, ideally expanded jet) using a local timestep factor of 10. the flow was convergerd to RMS 1e-04

Then i changed the timestep control to auto timescale in the results file from the previous simulation. the intermediate results show a totally different flow field from the semi-converged result (with local timestepping). The flow field shows the simulation (with auto timestepping) to be starting with the intial guess (not the results) for the local timestep simulation. Is there something i have missed with the intialization for the second simulation?

Is there a numerical issue with using extreamly small timesteps in regions where the flow is many time sllwer than in other regions of the flow field, apart from the obvious that the flow field will take ages to converge?

cheers nandu
  Reply With Quote

Old   September 5, 2002, 11:02
Default Re: Fatal over flow in solver
  #4
Robin
Guest
 
Posts: n/a
Hi Nandu,

Make sure you selected the Automatic with Value option for initial guess and not the Value option.

The Automatic with Value option tells the solver to use the existing solution if available, or the value you specified if there is no current solution. If you chose Value or Default, the solver will re-initialize the variables on restart.

See the on-line help for more details.

Regards, Robin
  Reply With Quote

Old   September 5, 2002, 11:33
Default Re: Fatal over flow in solver
  #5
Nandu
Guest
 
Posts: n/a
thanks Robin, u've been a huge help

cheers nandu
  Reply With Quote

Old   September 16, 2002, 08:19
Default Re: Fatal over flow in solver
  #6
Dave
Guest
 
Posts: n/a
Hi Nandu could you explain to me what the Local Time stepping Factor is ? I have read the on line manual and have managed to only confuse myself. Cheers Dave
  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
Suitable solver for Air/Air flow with different temperatures cjm OpenFOAM 1 January 20, 2011 05:17
Troubleshooting Unsteady Incompressible Flow Solver dandalf Main CFD Forum 0 November 15, 2010 11:55
What solver to use for inviscid flow simulation over missile mecbe2002 OpenFOAM 0 April 27, 2010 12:10
Inviscid flow solver luca_g OpenFOAM Running, Solving & CFD 0 December 21, 2006 13:55
Inviscid solver : separation of the flow Jean-Marie Cavet FLUENT 1 September 2, 2003 13:32


All times are GMT -4. The time now is 17:34.