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

Negative Densities

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 24, 2005, 09:14
Default Negative Densities
  #1
shyam
Guest
 
Posts: n/a
Hi All,

My run is coming out by giving -ve densities found in more than 100 cells. The fluid is air with f(T,P) setting. Domain size is 1km. shape is spherical. Velocity inlet is given by pressure UV explicit method. I use MARS scheme.

Kindly guide.

Thanks

  Reply With Quote

Old   April 24, 2005, 22:32
Default Re: Negative Densities
  #2
varun
Guest
 
Posts: n/a
Play with the relaxation factors. Reduce them even then if it doesnt work,then reduce the time step it will surely work
  Reply With Quote

Old   May 8, 2005, 07:17
Default Re: Negative Densities
  #3
Ant
Guest
 
Posts: n/a
My technique! The combination of relaxation factors helps me for various compressible steady problems: velocity=0,2; pressure=0,1; turbulence=0,5; density and turb.visc.=0,5; and for entalphy you can keep ones by default. However, if the solution doesn't converge you have to issue the relaxation factor for entalphy equal 0,1. And reduce the values of residual tolerance to 10e-6 for pressure, 10e-18 for temperature, and others to 10e-2. If this combination doesn't work you should go on a transient solver! For transient problems only time step reducing delivers from negative density!
  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
negative densities john Siemens 0 March 19, 2008 07:32
negative densities Riyaz Ahamed Siemens 2 August 14, 2007 02:47
Negative Densities Chris Siemens 4 June 25, 2007 09:39
negative densities CMB Siemens 4 January 4, 2004 03:41
negative densities. Mihir Siemens 4 December 9, 2002 22:04


All times are GMT -4. The time now is 08:41.