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

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August 16, 2013, 06:23 
The formula to compute the mass flow averaged value in a surface

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Meimei Wang
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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.
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August 16, 2013, 06:35 

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Mr CFD
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Someone correct me if I'm wrong, but isn't just areaAvg(massflow)@location?


August 16, 2013, 07:33 

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OJ
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August 17, 2013, 06:08 

#4  
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Meimei Wang
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Quote:
Where did you find it? Any CFX tutorial?
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August 17, 2013, 06:37 

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Mr CFD
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..........


August 17, 2013, 09:32 

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Meimei Wang
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I'm asking about the math averaging algorithm that CFX use to compute. Not the command.
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August 17, 2013, 09:54 

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OJ
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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, 09:59 

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Meimei Wang
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Where did you find this formula? How do you know CFX use this formula?
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August 17, 2013, 10:09 

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OJ
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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, 10:11 

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September 1, 2013, 19:39 

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Glenn Horrocks
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Yes, sum up the cell volumes.


September 3, 2013, 08:05 

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Meimei Wang
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How do you know that? Any reference?
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September 3, 2013, 20:08 

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Glenn Horrocks
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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, 14:43 

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Meimei Wang
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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?
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September 6, 2013, 18:06 

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Edmund Singer P.E.
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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, 20:07 

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Mr CFD
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1. Mesh issues 2. A lack of understanding 3. A combination of 1 and 2 

September 7, 2013, 06:03 

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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, 06:17 

#18  
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Meimei Wang
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And what is the formula to compute the surface averaged heat flux?
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September 7, 2013, 06:37 

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Meimei Wang
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September 7, 2013, 12:40 

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