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

negative densities.

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

Reply
 
LinkBack Thread Tools Display Modes
Old   December 5, 2002, 11:38
Default negative densities.
  #1
Mihir
Guest
 
Posts: n/a
HI, I'm performing a full cycle IC Engine simulation under motoring conditions. I start with the exhaust stroke and then move on to intake,compression and expansion strokes.During the run,just at the beginning of the compression stroke i get the foll. error:

Error#076 Negative densities at more than 100 cells.Run stopped.

Does anyone know the cause of this error and how to resolve the same? thanx in advance

Mihir.

PS: I'm using ideal f(T,P) for density.
  Reply With Quote

Old   December 6, 2002, 01:03
Default Re: negative densities.
  #2
nikhil
Guest
 
Posts: n/a
hi mihir, since u r using ideal gas f(t,p) for density..density is also variable.so what would be happening in ur case due to very high relaxation factor for density at any iteration the density would be coming negative. decrease the relaxation factor for density until u did not get these error.u can do this also decreasing both pressure and density factor at a time. let me inform if u get out the problem. nikhil
  Reply With Quote

Old   December 6, 2002, 08:48
Default Re: negative densities.
  #3
Mihir
Guest
 
Posts: n/a
HI Nikhil, thanx for replying.I've already played with the relaxation factors with no result.could it be a problem with the mesh? I have used the vc3dgen command in the cylindrical co-ordinate system to generate the cylinder cells.Hence the central cells are all prismatic.But STAR-CD considers prismatic cells as hexa cells collapsed along a face.So could it be that these cells are treated as cells with a high aspect ratio?Let me know if u have some info on that front. Thanx again.

Mihir.
  Reply With Quote

Old   December 9, 2002, 03:54
Default Re: negative densities.
  #4
user
Guest
 
Posts: n/a
Have a look at the statements posted here in former times
  Reply With Quote

Old   December 9, 2002, 22:04
Default Re: negative densities.
  #5
CJ Tune
Guest
 
Posts: n/a
Also, try using finer time steps -be mindful of your Courant number. This error could happen too when joining back previously excluded cells regions. There are a couple of articles on ICE sims on www.adapco-online.com.
  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
negative densities john CD-adapco 0 March 19, 2008 07:32
negative densities Riyaz Ahamed CD-adapco 2 August 14, 2007 01:47
Negative Densities Chris CD-adapco 4 June 25, 2007 08:39
Negative Densities shyam CD-adapco 2 May 8, 2005 06:17
negative densities CMB CD-adapco 4 January 4, 2004 03:41


All times are GMT -4. The time now is 20:05.