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

3-D Compressible Flow Boundary Conditions

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 4, 2009, 17:07
Default 3-D Compressible Flow Boundary Conditions
  #1
Tyler
Guest
 
Posts: n/a
I am having problems with convergence on a 3-d compressible external flow problem. I am trying to model Mach 0.8 axial flow around a solid cylinder. The flow field is external, so I have tried using "pressure far-field" boundary conditions on the 6 faces of the flow field volume. However, whenever I run the simulation, I can never get convergence with the continuity equation. I also get errors stating the pressure and temperature have been limited to a certain value.

The flow volume is a rectangle with a cylinder in the middle. No elements are even close to being skewed, so I don't think it is a mesh problem. Are there better/more appropriate boundary conditions for external flow? Any help or assistance is greatly appreciated. Please let me know if more details are needed.

-Tyler
  Reply With Quote

Old   February 4, 2009, 21:24
Default Re: 3-D Compressible Flow Boundary Conditions
  #2
NRD
Guest
 
Posts: n/a
How about specifying non-reflecting boundary conditions?
  Reply With Quote

Old   February 5, 2009, 08:53
Default Re: 3-D Compressible Flow Boundary Conditions
  #3
VAMSIDHAR
Guest
 
Posts: n/a
Dear Tyler,

Getting convergence with compressible flow is not easy .first see whether the domain you have conseidered is enough or not.Then try with pressure inlet or mass flow inlet boundary condtion at inlet and pressure outlet condtion at outlet.Also you can use wall with large doamin or pressure far feild or opening.but initially try with pff.Also see that the domain is properly considered.that is very important for convergence. cheers, vamsi

  Reply With Quote

Old   February 5, 2009, 14:29
Default Re: 3-D Compressible Flow Boundary Conditions
  #4
sa
Guest
 
Posts: n/a
might be the probelm is essentially unsteady, so you wont be able to get convergene with steady state sover
  Reply With Quote

Old   February 5, 2009, 20:58
Default Re: 3-D Compressible Flow Boundary Conditions
  #5
zongtwi
Guest
 
Posts: n/a
My personal experience for converging compressible cases is to start slow. Use the pressure far field and start from a relatively low Mach number. Say 0.3. Then run the simulation until it is converged, and increase the spped to Mach 0.5 say...and then to 0.7 and 0.8.

Another reason it is not converging well is that there might be some local areas where the speed has reached sonic or supersonic conditions, and thus a shock might occur locally, but your mesh size is too coarse to capture it. Try to use mesh adaption with a criteria of pressure gradient say, and see what you get.

Hope that helps.
  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
boundary conditions in compressible flow mohnish FLUENT 3 March 9, 2007 04:58
boundary conditions compressible flow newposter Main CFD Forum 4 June 16, 2006 18:10
boundary conditions for compressible flow George Main CFD Forum 12 March 16, 2005 10:26
compressible flow boundary conditions ravi FLUENT 2 December 15, 2004 05:28
compressible flow boundary conditions yangqing FLUENT 2 January 22, 2002 11:19


All times are GMT -4. The time now is 21:34.