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

A probelm on the pressure

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 7, 2000, 16:43
Default A probelm on the pressure
  #1
John
Guest
 
Posts: n/a
Hi, there,

I have a problem in understanding the role that the pressure (p) plays in NS equations. It is well known that only the pressure gradients contribute to the flow motion. You can force the pressure at any point in the flow domain to zero as a reference datum. But, for outgoing flows, one can set the traction (Fx, Fy) at the exit face to vanish:

Fx = (-p + 2/Re du/dx) nx + (du/dy + dv/dx) ny = 0 Fy = (dv/dx + du/dy) nx + (-p + 2/Re dv/dy) ny = 0

in which (nx, ny) is the direction vector normal to the exit. The problem is that the pressure at the exit can be any value if different reference points are set. What would you say?

Regards,
  Reply With Quote

Old   November 8, 2000, 10:24
Default Re: A probelm on the pressure
  #2
Chidu
Guest
 
Posts: n/a
Hi John,

The "system" pressure drops out of the NS equations only for incompressible flows since density no longer depends on pressure. So your first point is valid only under this constraint.

As far as the traction condition, is this intended for internal flows or external flows? By that I mean is your boundary near to a wall or far away from a wall? Somehow, I need something more concrete to proceed ahead.

regards, chidu...
  Reply With Quote

Old   November 8, 2000, 12:49
Default Re: A probelm on the pressure
  #3
John
Guest
 
Posts: n/a
Hi, Chidu,

Thx for your reply. You are right that I was talking about the incompressible viscous flow. And, the traction BC will be applied to the external flow that the boundary is far away from a wall.

regards,

  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
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 06:27
Using pressure outlet BC Shreyansh FLUENT 0 November 5, 2010 15:57
Setup/monitor points of pressure and force coefficients siw CFX 3 October 22, 2010 06:07
Pressure Condition sidd CD-adapco 0 April 2, 2007 09:31
Setting pressure and velocity in inlet Asghari FLUENT 5 September 22, 2006 13:23


All times are GMT -4. The time now is 04:50.