Hi!

I have calculated the air flow in a some kind of tube. I am now supposed to get the friction factor on the wall. How can I get it?

Thanks!

the getw command will give you the wall forces. from their you will need to do a little algebra.

Ok, I see. With GETW I can obtain force, stress, and so on. But there is no friction coefficient... You said I should do a little algebra? I know friction is related to stress but I don't know how to use this.

I don't even know how to use the GETW function, to select my wall, etc.

Thanks!

It all depends upon the definition you have for friction coefficient.

Use boundary, vertex, and cell sets to look at the wall. Use getw to select the wall force or stress. The commnad "summ cset " will then give you max, min, and average quantities over that wall.

Apply your definition & you have friction factor.

can anyone define friction factor and use of friction factor

Friction factor should be the actual flow vs. ideal.

Hi all,

The friction factor for wall depends only upon Reynolds number if it is laminar flow and depends upon the roughness and the Reynolds number if it is turbulent flow.

You have to take length of the computational model almost 20 times of the dia (if it is circular cross section) or hydraulic dia (if it is no circular cross section).

In order to calculate friction factor, you have to calculate pressure gradient means pressure difference over a particular length. It is the best to calculate at the end of the geometry near the outlet but 5 to 6 cells before outlet. From the pressur difference and length , hydraulic dia and density (see the formula for friction factor online)you can calculate friction factor.

I hope this helps.

Sachin