
[Sponsors] 
The formula to compute the mass flow averaged value in a surface 

LinkBack  Thread Tools  Display Modes 
August 16, 2013, 05:23 
The formula to compute the mass flow averaged value in a surface

#1 
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Hi
May I ask where could I find the formula that CFXpost use to compute the mass flow averaged value in a surface? I checked the CFX tutorial but didn't find it. If tutorial does include this formula, please let me which tutorial and which page. Thanks.
__________________
Best regards, Meimei 

August 16, 2013, 05:35 

#2 
Senior Member
Mr CFD
Join Date: Jun 2012
Location: Britain
Posts: 314
Rep Power: 7 
Someone correct me if I'm wrong, but isn't just areaAvg(massflow)@location?


August 16, 2013, 06:33 

#3 
Senior Member
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 12 

August 17, 2013, 05:08 

#4  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
Where did you find it? Any CFX tutorial?
__________________
Best regards, Meimei 

August 17, 2013, 05:37 

#5 
Senior Member
Mr CFD
Join Date: Jun 2012
Location: Britain
Posts: 314
Rep Power: 7 
..........


August 17, 2013, 08:32 

#6 
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
I'm asking about the math averaging algorithm that CFX use to compute. Not the command.
__________________
Best regards, Meimei 

August 17, 2013, 08:54 

#7  
Senior Member
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 12 
Quote:
Please read the second in the formula as v. Thus, more formally, the formula is = where are the local velocity vector, local density and the area vector at facet of the local cell respectively. OJ 

August 17, 2013, 08:59 

#8  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
Where did you find this formula? How do you know CFX use this formula?
__________________
Best regards, Meimei 

August 17, 2013, 09:09 

#9 
Senior Member
OJ
Join Date: Apr 2012
Location: United Kindom
Posts: 475
Rep Power: 12 
Have a look at documentation, stitch the information together and apply judgement...
CFX: http://www.sharcnet.ca/Software/Flue.../i1308570.html FLUENT: http://www.sharcnet.ca/Software/Flue...th/node416.htm OJ 

September 1, 2013, 09:11 

#10  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
__________________
Best regards, Meimei 

September 1, 2013, 18:39 

#11 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,196
Rep Power: 102 
Yes, sum up the cell volumes.


September 3, 2013, 07:05 

#12 
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
How do you know that? Any reference?
__________________
Best regards, Meimei 

September 3, 2013, 19:08 

#13 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,196
Rep Power: 102 
Isn't it obvious? If you break up a volume into zillions of little volumes then the sum of those little volumes is the total volume. It is hardly rocket science.


September 6, 2013, 13:43 

#14  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
Yes. It is obvious that we can compute it in this way. But it is not obvious that CFX choose this way to compute the volume. Any CFX reference about it?
__________________
Best regards, Meimei 

September 6, 2013, 17:06 

#15 
Senior Member
Edmund Singer P.E.
Join Date: Aug 2010
Location: Minneapolis, MN
Posts: 512
Rep Power: 12 
If you are worried about how CFX calculates the total volume and need a reference for it, then I think you have your work cut out for you.
You are heading towards questioning every single equation, which is quite a task. Are you getting a huge discrepency in the CFX calculated volume as opposed to the CAD? If so, I would question your mesh resolution first prior to blaming the software. 

September 6, 2013, 19:07 

#16  
Senior Member
Mr CFD
Join Date: Jun 2012
Location: Britain
Posts: 314
Rep Power: 7 
Quote:
1. Mesh issues 2. A lack of understanding 3. A combination of 1 and 2 

September 7, 2013, 05:03 

#17 
New Member
Join Date: Oct 2011
Posts: 20
Rep Power: 7 
Remember only mesh goes into solver not real geometry. It must be cell volume or calculation through cell edges but if ur mesh is close to geometry solver volume will match the real geometry.
Anyhow domain volume in not used in discretized eqn so it wont effect CFX solution. But If you have compromised on geometry to improve mesh quality then you should use volume from preprocessing for calculation or expresion in CFX 

September 7, 2013, 05:17 

#18  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
And what is the formula to compute the surface averaged heat flux?
__________________
Best regards, Meimei 

September 7, 2013, 05:37 

#19  
Senior Member
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 8 
Quote:
__________________
Best regards, Meimei 

September 7, 2013, 11:40 

#20 
Senior Member
Mr CFD
Join Date: Jun 2012
Location: Britain
Posts: 314
Rep Power: 7 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Surface inejction steady state  mass flow rate  CFDstudent  FLUENT  0  January 25, 2012 14:40 
Discrete Phase & Mass Flow Rate  MagnusZeus  FLUENT  0  December 2, 2011 18:57 
Mass Flow Rate on the Interior Surface  Barii.Johnason  FLUENT  24  May 11, 2007 17:59 
Mass flow Averaged quantities  Fred  CDadapco  5  July 5, 2005 02:05 
Target Mass Flow Rate  Nitin  FLUENT  6  March 12, 2004 06:39 