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June 13, 2011, 06:40 
Friction Factor Calculation in Pipe

#1 
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Morteza
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Dear Friends
I have modelled a 3d pipe in Gambit and Fluent. To validate the results I have to calculate the friction factor in the pipe. There are so many threads in cfdonline , but there is not any satisfying response. I read in a tutorial that I have to calculate the friction factor using the below formula: f=(8*shear stress)/(density* average velocity^2) But, the question is here, how can I calculate the mean velocity? in which plane i have to calculate that? and how to calculate the shear stress? the pipe diameter : 0.12m velocity : 12.17 m/s along negative z Please read the attached file. thank you in advance Morteza If you like send you the full version of the attached pdf, please write your emails down. 

June 13, 2011, 07:19 

#2 
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The file you attached answers all your questions as far as I see it.
It describes how to calculate mean velocity and the shear stress as well as in which plane you are supposed to calculate them. Are there any hidden problems in your questions that I missed?
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June 13, 2011, 07:31 

#3  
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Morteza
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Quote:
Dear Ford Perfect showed in the file that I must create an ISOSURFACE for calculating the mean velocity and stress. I found that tutorials creat the surface in the last section of the pipe(exit plane)... but I am puzzled in assigning an ISOvalue for this surface. as well, I think the tutorials chose the zcordinate according its own model. In what coordinate i have to create the iso surface? my inlet plane and exit plane are located in xy . and the axis of the pipe is along the negative z axis. from (0,0,0) to (0,0,0.12) reynolds number: 100000 diameter: 0.12 inlet velocity: 12.17 m/s 

June 13, 2011, 07:46 

#4 
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Just "surface > iso surface" then pick surface of constant "mesh > zcoordinate" assuming that zcoordinate is in the axial direction. Then you have to choose where you wish to create the surface along the axis.
If you like you can also pick the outlet surface directly since that is already present in your model.
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"Trying is the first step to failure."  Homer Simpson 

June 14, 2011, 14:41 

#5  
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Morteza
Join Date: May 2010
Location: Iran,Islamic Republic of
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Quote:
I did all according the file. I created an ISOSURFACE at the outlet plane of the pipe.... I calculated the shear stress on the wall as the tutorial did. and also the average velocity. but I think the calculated value of friction factor is wrong. It is something two times more than the value of moody diagram. the tutorial has modeled half of a pipe. But i modeled the entire pipe. Isn't it the reason for nonsatisfying value of friction factor??? please help me... It's very emergency... 

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