[medguedem]

I have modelled a 3d pipe in Gambit and Fluent To validate the results I dont know how can I calculate the friction factor in the pipe.as (L. F. Moody diagram, "Factors of friction for the flow of the pipes).
There are so many threads in cfd-online , but there is not any satisfying response.
I am looking for a tutorial or youtub that have to calculate the friction factor and how i can to calculate the shear stress?

[Simbelmynë]

If the flow is laminar (Re < 2100) then the friction factor can be found from 16/Re.


If the flow is turbulent (Re>4000) then you need to know the relative surface roughness of the pipe as well as the Reynolds number in order to find the friction factor.


The pressure drop along a pipe also suffers from entry effects which are not normally accounted for in the Bernoulli + Moody diagram technique. The same applies to your simulation.


The velocity profile for the laminar case can be found from the Hagen-Poiseuille equation. You can apply Newton's law of viscosity to find the shear stress at the wall.


The velocity profile for turbulent flow is different, but there are references with empirical formulas (e.g. here).

[medguedem]

thank you very much for your answer Simbelmynė.
I know the theoretical formulas of coeifficient of friction and pressure, but the problem that remains posed is the tool of the simulation fluent ansys I have not succeeded to find the exact value of friction and the hydraudynamic force of our simulation. I need tutorial or steps followed to calculate the friction factor and u* the friction velocity (u* = √τ w/ρ ) and Nikuradse formule
1/√f=-0.861ln[(ε/D)/3.7+2.21/Re√f]
please specifics

[Simbelmynë]

First, if this is a Fluent specific problem then you should post it under that forum, not the main forum.


In order to find custom expressions in Fluent, you can create a "custom field function", using the interface. You can then calculate the area-weighted average, of that function, over the wall using the surface integral functionality in Fluent.