[morteza08]

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 cfd-online , 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.

[Ford Prefect]

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?

[morteza08]

Originally Posted by Ford Prefect

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?

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 ISO-value for this surface. as well, I think the tutorials chose the z-cordinate 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

[Ford Prefect]

Just "surface > iso surface" then pick surface of constant "mesh > z-coordinate" assuming that z-coordinate 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.

[morteza08]

Originally Posted by Ford Prefect

Just "surface > iso surface" then pick surface of constant "mesh > z-coordinate" assuming that z-coordinate 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.

Dear friend
I did all according the file.
I created an ISO-SURFACE 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 non-satisfying value of friction factor???
please help me... It's very emergency...

[mohamednasser]

can you send me the tutorial
m.nasser@zu.edu.eg

[f.kh]

I have the same problem.
I would be grateful if you send me the tutorial.

F.khanmohammadi@stu.nit.ac.ir

[rifat ahamed]

I am facing the same problem,

I have a curved corrugated pipe with E shaped baffles. total pipe length is 3.2m and the hydraulic diameter is 0.1333. pressure drop came out 31.992148Pa. but after calculating the friction factor it came 2.702848606 for a Reynolds number of 5000.

can you please help me ?

mail: rifatahamed@iut-dhaka.edu