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

Question about the outlet boundary condition.

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 26, 1999, 20:29
Default Question about the outlet boundary condition.
  #1
G.H.Lee
Guest
 
Posts: n/a
Hello! I am simulating the impeller passsage flow in centrifugal compressor. As far as I konw, impeller passage is short, thus I think it is difficult to apply outlet boundary condition. Neumann condition (gradient of variable is zero) is not appropriate. Would you like to inform me a best way. Thank you.
  Reply With Quote

Old   April 27, 1999, 04:04
Default Re: Question about the outlet boundary condition.
  #2
mahesh prakash
Guest
 
Posts: n/a
Hi, Have you tried using a pressure boundary condition? Regards
  Reply With Quote

Old   April 27, 1999, 14:39
Default Re: Question about the outlet boundary condition.
  #3
Richard Carroni
Guest
 
Posts: n/a
Hi, a colleague of mine is working in a similar area (looking at inlet guide vanes). Knowing the mass flow rate, he estimated the pressure at the exit, and then ran the simulation to find the new mass flow rate. The exit pressure was then revised accordingly. This procedure was iterated until the simulated mass flow rate (obtained with the estimated exit pressure) coincided with the actual mass flow rate.

Hope this helps.

rich
  Reply With Quote

Old   April 28, 1999, 05:49
Default Re: Question about the outlet boundary condition.
  #4
JS
Guest
 
Posts: n/a
But usually the mass flow rate is already given at the inlet. Which inlet condition was choiced by him ?
  Reply With Quote

Old   April 28, 1999, 12:35
Default Re: Question about the outlet boundary condition.
  #5
John C. Chien
Guest
 
Posts: n/a
(1). For turbomachinery computations, especially the compressible flow cases, the total pressure and total temperature are specified at the inlet, with velocity, static pressure and density updated from each iteration. The outlet condition is the specified static pressure. (2). One can use the specified conditions to obtain one converged solution. Or one can zoom in the outlet static pressure to obtain a solution with the target flow rate. (3). Given enough distance from the blade trailing edge, the parallel downstream condition can be used with the specified inlet velocity. There will be some up-stream effect of downstream condition, but that's life. It is problem dependent.
  Reply With Quote

Old   April 29, 1999, 05:50
Default Re: Question about the outlet boundary condition.
  #6
Richard Carroni
Guest
 
Posts: n/a
My fault; I should have been more specific. A total pressure is applied at the inlet (based on atmospheric pressure and inlet bulk velocity) and the static pressure (estimated) is applied at the outlet. The static pressure is continuously updated until the predicted mass flow rate coincides with the actual (known) value.

rich
  Reply With Quote

Reply


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
inlet velocity boundary condition murali CFX 5 August 3, 2012 09:56
Transient outlet boundary condition problem jwillie2000 CFX 1 December 7, 2009 18:07
Outlet boundary condition =/ AdidaKK CFX 4 December 4, 2009 09:12
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05
New topic on same subject - Flow around race car Tudor Miron CFX 15 April 2, 2004 07:18


All times are GMT -4. The time now is 16:03.