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

Atmospheric conditions at boundary

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 11, 2008, 23:18
Default Atmospheric conditions at boundary
  #1
JP
Guest
 
Posts: n/a
Hello All,

I have a **large** cylindrical volume. Inside the air is modeled as ideal-gas, compressible fluid. All the walls of the cylinder are supposed to represent infinity: 1 atmosphere, T=300K air. Flow at these walls may happen in any direction.

How do I define these walls? Any ideas are appreciated.

(I tried setting one base and the cylinder wall as pressure-inlets, the other base as pressure far-field. I left all settings at default. I am not sure is this the right way to do it?)
  Reply With Quote

Old   October 12, 2008, 02:14
Default Re: Atmospheric conditions at boundary
  #2
doki
Guest
 
Posts: n/a
what is the flow mach number? for M>=0.6 it is recommended to use pressure far field. to do this, you should have a really large volume. if not, generally you should define the BCs as pressure inlet and outlet.
  Reply With Quote

Old   October 12, 2008, 09:35
Default Re: Atmospheric conditions at boundary
  #3
JP
Guest
 
Posts: n/a
Hi,

Thank you for your reply. In the center of domain the flow is subsonic (but close to speed of sound). I am not sure what is the flow speed close to the far boundaries. This is my problem. But I expect it to be 5-20 times slower compared to center of domain.

1) Pressure far-field means flow out, no backflow (maybe I am wrong?). I can't do this, because backflow should occur, as colder air flows into my warmer domain.

2) Pressure intlet/outlet seems better. Here I can fix p=1atm T=300K The problem is I have to fix inflow/outflow kinetic parameters and I don't know what these values are.

Any ideas are appreciated.

  Reply With Quote

Old   October 14, 2008, 06:30
Default Re: Atmospheric conditions at boundary
  #4
Prasad
Guest
 
Posts: n/a
Option 2 in your mind (pressure outlet) seems to be appropriate. You can choose back flow direction specification method as 'from neighboring cell'. You may choose k-e turbulent specification method with values 1-3 but that depends upon your specific case.
  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
how to simulate the atmospheric pressuer boundary sam FLUENT 1 February 15, 2007 17:50
How to generate a atmospheric boundary layer Morten Andersen CFX 3 January 16, 2007 07:48
Top boundary in a entrainment atmospheric BL Reginaldo Paula FLUENT 0 May 9, 2006 16:38
Atmospheric Boundary Layer Lennart FLUENT 1 June 26, 2003 10:19
Atmospheric boundary layer modelling James Forrest FLUENT 3 April 17, 2003 11:09


All times are GMT -4. The time now is 20:27.