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December 11, 2012, 13:40 
Mass Weighted Average

#1 
Member
Brock Lee
Join Date: Sep 2012
Location: Midwest
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Hey guys, I'm looking to calculate a mass weighted average over a faceZone for pressure using swak4foam. Specifically, this is the equation I'm trying to implement...
Capture.PNG My question comes when trying to implement. Is it possible in swak4foam to divide a sum by a sum within one expression? Can I do two sums separately and divide them? So far I've only seen expressions that can do one accumulation, such as the one below for mass flow rate... Code:
massin { type swakExpression; valueType faceZone; zoneName interiorinlet1; expression "phi*flip()"; accumulations ( sum ); verbose true; autoInterpolate true; } 

December 11, 2012, 17:32 

#2 
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Brock Lee
Join Date: Sep 2012
Location: Midwest
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Ok, I think I found an equivalent expression. The following function I believe does what I need it to do...
Code:
p_stat2 { type swakExpression; valueType faceZone; zoneName interiorinlet1; expression "(p*phi*flip())/sum(phi*flip())"; accumulations ( sum ); verbose true; autoInterpolate true; } Also, does anyone know if when you have backflow on a face, does it register as negative mass flow using the phi*flip() formulation? Last edited by GRAUPS; December 12, 2012 at 12:37. 

December 12, 2012, 18:48 

#3  
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Bernhard Gschaider
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Quote:
Yes. You should get the correct backflow if you use flip() (the sign of phi depends on the orientation of the face. Multiplying with flip() "removes" that dependence)
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December 12, 2012, 19:34 

#4  
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Brock Lee
Join Date: Sep 2012
Location: Midwest
Posts: 40
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Quote:
Fantastic, just wanted to make sure. Thanks for your replies. 

November 26, 2015, 04:51 

#5 
New Member
Join Date: Jul 2013
Posts: 8
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Dear Foamers,
I want to use groovybc, in order to create a T bc for a reciculation device. To do this I have do calculate the massfluxweighted temperature of a face. I use the following code: PHP Code:
Thank's in advance 

May 3, 2019, 08:28 
Mass averaged weighted kinetic energy

#6 
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@moon
Join Date: Apr 2019
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Hi guys
I am trying to calculate mass average weighted kinetic energy for Tank sloshing case. The equation is similar to the one discussed in this thread. (summation(mass*0.5*U*U)/ summation (mass)) Can someone help me with the syntax to write this expression using swak4Foam ? Iam new to openFoam. any help will be highly apreciated. Thank you. 

May 3, 2019, 09:34 

#7  
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Bernhard Gschaider
Join Date: Mar 2009
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Quote:
The expression for the total mass would be (assuming you have the denisty in a field rho) "sum(vol()*rho)". The sum of the kinetic energy would be "sum(vol()*rho*0.5*(U&U))" (using & for the scalar product). Now with swakExpression you could write the complete expression as "(vol()*rho*0.5*(U&U))/sum(vol()*rho)" (without the sum) and in the accumulationslist use "sum". Or you write the equation with the sum and in the accumulations use one of "min", "max", "average". But the first option needs a little less computation
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May 6, 2019, 05:38 

#8  
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@moon
Join Date: Apr 2019
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Quote:
The equation is writing results perfectly. But I dont understand the logic behind using summation in the numerator for calculating max, min, average and not using summation for calculating sum (accumulation). the equation calculates mass average weighted kinetic energy for each cell in the domain for each timestep and calculates sum. where is the difference coming by introducing the summation in the numerator ? There is something that I am missing out in understanding here. Can u please explain this?? Thanks in advance 

March 16, 2021, 14:41 

#9 
New Member
Join Date: Oct 2019
Posts: 11
Rep Power: 3 
Hello Foamers,
I'm new in OF, I'm studying compressible flows and for postprocessing, I just want to have confirmation. I'm not sure about syntax, but I would like to calculate the massweighted average of one variable, defines as at my "r1outblockoutflow" (patch name)' so is it correct to write in my controlDict (OpenFOAM v2006) Code:
weightAvgOut { #includeEtc "caseDicts/postProcessing/surfaceFieldValue/surfaceRegion.cfg" regionType patch; name "r1outblockoutflow"; operation weightedAverage; weightField phi; fields (p T Ma total(p)); writeInterval 5; log true; } Also, does anyone know if OF can provide the total temperature? 

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mass weighted average, swak4foam, swakexpression 
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