Comparing CFD pressure loss results to Blasius and Darcy equations

[Isabella F]

Hi everyone. i have done a CFD smulation in fluent for a turbulent pipe flow and have plotted static pressure against distance x. from the graph i get a straight negtive gradient. i have been told that you should compare the pressure loss to Blasius equation and Darcy equation. How do i compare the pressure loss to this. thank you. the fluid is water, diameter is 50mm, inlet velocity is 1m/s and reynolds number 49760.
heres is the xy plot i get.

 

[boneh3ad]

Well that seems awfully silly to compare to Blasius because (A) it is pipe flow, so Blasius is not representative, and (B) it is turbulent, so Blasius doesn't apply.

Comparing to Darcy-Weisbach should be straightforward though.

 

[Isabella F]

The Blasius friction factor f=0.079/(Re^0.25).
Is there a way to calculate friction factor from the presure drop? that is what i think i need to do and then compare to blasius friction.

 

[boneh3ad]

Ah, I thought you were referring to the Blasius boundary layer. My mistake.

 

[Isabella F]

How do i do this then. I am a bit confused.

 

[boneh3ad]

Just look up the Darcy-Weisbach equation. It is very straightforward. Use it and the Blasius correlations to approximate the theoretical pressure loss (head loss) and compare to your results.