CFD Online Logo CFD Online URL
Home > Forums > FLUENT

On the pressure far-field boundary condition

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

LinkBack Thread Tools Display Modes
Old   March 24, 2005, 09:13
Default On the pressure far-field boundary condition
Posts: n/a
Hello everyone, I am simulating the jet flowfield. I set the pressure far-field boundary conditions for the outside region, but the flow (outside) is not symmetric. while not setting the symmetry boundary conditions, I think the flow should be also right. Why ? I doní»t know the reason, please help me. Thanks.
  Reply With Quote

Old   March 24, 2005, 09:32
Default Re: On the pressure far-field boundary condition
Posts: n/a
I'm not entirely sure what the problem is... from the sound of it you have asymmetric flow when using the pressure far field, and you think your flow should be symmetric even though you didn't use a symmetry boundary condition... is this close?

Pressure far field condition needs to be far away from any geometry so that it is seeing clean flow. Problems arise when upstream or downstream effects of the geometry intersect the pressure far field. For an airfoil the general rule is 5 to 10 chords in all directions. If separation is going to occur, then you probably want to consider having at least 10chords downstream. In high speed flow, with shocks for especially, you probably want to consider being about 10 or more chords perpendicular to the flow so that the shock can dissipate before intersecting the BC.

Your grid can also cause assymetries. Quick example, lets say you have a symmetric airfoil with a coarse mesh on the underside and refined mesh on the topside. This is going to cause an assymetry in the calculation of the flow and you'll get some lift value on the airfoil even though you're at 0deg AoA. If your mesh isn't set up properly, it doesn't take much of a difference in the the upper and lower mesh to create a slight pressure difference, which leads to asymmetric loads.

I hope something in this was helpful.

Goodluck, Jason
  Reply With Quote

Old   March 24, 2005, 21:28
Default Re: On the pressure far-field boundary condition
Posts: n/a
I see, thanks. I will try to modify it.
  Reply With Quote

Old   March 25, 2005, 16:48
Default Re: On the pressure far-field boundary condition
Posts: n/a
Also check what boundaries touch the PFF boundary faces....E.g. you cannot have a pressure inlet/outlet touching a PFF wall.

  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
Pressure boundary condition C-H Kuo Main CFD Forum 18 September 16, 2016 03:19
Boundary condition in pressure equation Paolo Lampitella FLUENT 0 February 21, 2008 07:30
Question about pressure inlet boundary condition. Alina FLUENT 1 November 30, 2007 08:39
Neumann pressure BC and velocity field Antech Main CFD Forum 0 April 25, 2006 02:15
Pressure boundary condition Brindaban Ghosh Main CFD Forum 6 May 3, 2000 13:11

All times are GMT -4. The time now is 17:59.