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

BFS...again

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 19, 1999, 04:16
Default BFS...again
  #1
Jan Ramboer
Guest
 
Posts: n/a
Hello,

Here I am again with my backward facing step. I tried a few boundary conditions on the outlet. Now when I used the boundary condition on the Rieman invariants described by Hirsch, Internal and External flows. for the outflow. on the inflow I used an imposed velocity and temperature. Now it converge very wel but when convergence is almost reached it suddenly blows up. Is it because the outflow and inflow boundary conditions are incompatible?

Greetings,

Jan
  Reply With Quote

Old   August 19, 1999, 04:27
Default Re: BFS...again
  #2
John C. Chien
Guest
 
Posts: n/a
(1). Don't expect readers to dig up or guess at what you did before, if you expect interested readers to answer your question. (2). It is essential to state your problem in terms of: steady vs transient, laminar vs turbulent, compressible vs incompressible, and this Rieman invariant method. (3). Readers answer your question not just for you, it is for the rest of the readers. It is really expensive on Internet.
  Reply With Quote

Old   August 19, 1999, 05:40
Default Re: BFS...again
  #3
Jan Ramboer
Guest
 
Posts: n/a
OK let me state my problem again, I am solving a 2D compressible turbulent backward facing step (baldwin lomax model). At inlet I imposed a uniform velocity and temperature. 20 stepheights from the corner to develop the boundary layer. Reynolds is 37000 based on stepheight. At the outlet I used the rieman invariant boundary condition, (Rn=-abs(Vn)+2c/gamma-1). However when convergence is nearly reached, it explodes. Could it be that the two boundary conditions are not compatible?

Greetings,

Jan
  Reply With Quote

Old   August 19, 1999, 12:15
Default Re: BFS...again
  #4
John C. Chien
Guest
 
Posts: n/a
(1). I don't have the time to worry about whether the condition is properly coded. I am assuming that you are using the transient approach. (2). The suggestion is: find out the location where the calculation diverges. Plot the flow field ( or xy plot) before it diverges. Study the flow field evolution before it diverges. (3) In this way ,you can narrow down the location and the cause of the problem. You can also try a uniform mesh (uniform in x, uniform in y, separately) to elminate the mesh related causes. It is also important to mention whether it is transient formulation, or pressure based, or density based. The method of solution is also important along with the initial guess, the number of iteration at the time the solution diverges.
  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
My DES result about BFS! aladdincham Main CFD Forum 0 July 20, 2011 07:44
solving BFS with rhoTurbFoam in OpenFOAM 1.5 kiran OpenFOAM Running, Solving & CFD 0 June 11, 2010 00:36
Non-Newtonian Flow: Power law (2D BFS) hellouch FLUENT 3 April 21, 2009 03:03
Setup for laminar backward facing step (bfs) quarkz Main CFD Forum 13 September 30, 2005 09:51
BFS: steady? Jan Ramboer Main CFD Forum 1 September 9, 1999 14:04


All times are GMT -4. The time now is 02:58.