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

Question regarding surface integrals.

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

Like Tree2Likes
  • 1 Post By jsm
  • 1 Post By jsm

Reply
 
LinkBack Thread Tools Display Modes
Old   February 24, 2015, 14:02
Default Question regarding surface integrals.
  #1
New Member
 
Join Date: May 2014
Posts: 16
Rep Power: 4
techctrl is on a distinguished road
Hello,


If a surface integral value (such as pressure) is negative, what does it imply?

If I generate a force report in the positive Y direction for two horizontal walls, the vector value of one is positive and the other is negative. But the surface integral values of both (which are scalar values) are negative.

This has me confused, any clarification provided would be appreciated.
techctrl is offline   Reply With Quote

Old   February 26, 2015, 17:47
Default
  #2
jsm
Senior Member
 
JSM
Join Date: Mar 2009
Location: India
Posts: 168
Rep Power: 12
jsm is on a distinguished road
Hi,

You are comparing pressure and force that are entirely different. Don't compare the signs of these properties.

Pressure is scalar quantity and it has no signs. In general, fluent will show gauge pressure and it will not add the operating pressure. If it is confusing you, then plot the absolute pressure instead of static pressure. And the most possible reason for negative pressure is re-circulation nearer to the walls.

In other hand, force is vector quantity and what ever the sign you are getting in Fluent is the force acting direction.
techctrl likes this.
__________________
With regards,
JSM
jsm is offline   Reply With Quote

Old   February 27, 2015, 01:44
Default
  #3
New Member
 
Join Date: May 2014
Posts: 16
Rep Power: 4
techctrl is on a distinguished road
Quote:
Originally Posted by jsm View Post
Hi,

You are comparing pressure and force that are entirely different. Don't compare the signs of these properties.

Pressure is scalar quantity and it has no signs. In general, fluent will show gauge pressure and it will not add the operating pressure. If it is confusing you, then plot the absolute pressure instead of static pressure. And the most possible reason for negative pressure is re-circulation nearer to the walls.

In other hand, force is vector quantity and what ever the sign you are getting in Fluent is the force acting direction.
Thank you for the explanation.

You are correct that I shouldn't compare a scalar and vector quantity. I was mostly just curious as to why the pressure values end up being negative, which you clarified for me.

One more thing; does the pressure force on a wall surface and the pressure distribution on that same wall act in the same direction? If I were to draw the pressure profile on a wall surface, it should be in the same direction as the force vector, yes?
techctrl is offline   Reply With Quote

Old   February 28, 2015, 11:15
Default
  #4
jsm
Senior Member
 
JSM
Join Date: Mar 2009
Location: India
Posts: 168
Rep Power: 12
jsm is on a distinguished road
It is difficult to answer without considering the shape of wall and that is the reason we are using software to understand it.
techctrl likes this.
__________________
With regards,
JSM
jsm is offline   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
Error : Self intersecting surface mesh, computing intersections & Error : Impossible velan Open Source Meshers: Gmsh, Netgen, CGNS, ... 3 October 22, 2015 11:05
Problem with Gmsh nishant_hull Open Source Meshers: Gmsh, Netgen, CGNS, ... 23 August 5, 2015 02:09
Layers don't fully surround surface EVBUCF OpenFOAM Native Meshers: snappyHexMesh and Others 14 August 20, 2012 04:31
Worng values reported in surface integrals yashmash FLUENT 1 July 11, 2012 04:04
free surface flow simulation question Jane Main CFD Forum 0 April 22, 2004 13:25


All times are GMT -4. The time now is 18:15.