CFD Online Logo CFD Online URL
Home > Forums > FLUENT

how to prevent backflow?

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

LinkBack Thread Tools Display Modes
Old   June 20, 2007, 05:35
Default how to prevent backflow?
May Lim
Posts: n/a
Hi, I encountered backflow in my simulation. Once there's backflow, there is problem with convergence. Any suggestion to minimise backflow through the pressure outlet? Does an increase of total backflow temperature (default=300k) help?

Best regards, May
  Reply With Quote

Old   June 20, 2007, 08:17
Default Re: how to prevent backflow?
Posts: n/a
hallo, backflow doesn't necessary mean problem. It might be natural to the problem you are solving but you might consider extending computational domain at the outlet side so that you get more accurate result in the area close to the "backflow". The backflow might by because of some flow separation at wall or in the area where some kind of recirculation might be real. If the outlet BC is close to area of interest you shoud anlarge computational domain.

If it is the case of fluid flow in adverse pressure gradient (like compressor stage) you may start with low backpressure level and increase it succesively till you reaches some operation point that is of interest.

Another possible solution might be to set backflow direction from adjacent field and set reasonable value of backflow teperature (especially in compressible flow). a.

  Reply With Quote

Old   June 20, 2007, 12:17
Default Re: how to prevent backflow?
Posts: n/a
Hey May,

If you are modeling a flow in a region and extending the domain is a choice, please do so. The flow in this case will be uniform by the time it reaches the outlet BC. No one can tell you how far you should go; so use your imagination! Don't forget that "Pressure-outlet" BCs are more stable that "Outflow" BCs, since pressure is perdefined beforehand there. If you are using Pressure-outlet, you can specify the "backflow total temperature". Change it to the average temperature at the outlet of your domain. (in case backflow exists, the cells adjacent to the outlet will be assigned this temperature, it helps!). How many outlets do you have in your domain? More than one? If so, never use both the pressure-outlet and the outflow together (they hate each other!).

Kind Regards
  Reply With Quote


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
How to prevent backflow when airfoil starts heaving quarkz ANSYS 0 July 14, 2011 11:03
Modeling Backflow for a 3D Airfoil (Wing of Finite Span) Josh CFX 9 August 18, 2009 11:31
backflow temperature specification jonglee FLUENT 0 April 20, 2007 04:57
Problem with integrals and averages if backflow?? Amit FLUENT 0 October 19, 2006 18:54
Swirl in backflow on pressure outlets Jonas Larsson FLUENT 17 February 3, 2000 03:14

All times are GMT -4. The time now is 10:12.