# How to get the velocity of the air flow according to a propeller angular velocity ?

Hello

I'm a student and I have to realize a wind tunnel, so I found out an old propeller from an old fan and I modeled it.

Thanks to Andreas Gkertsos's great tutorial (http://grabcad.com/questions/tutorial-how-to-do-a-flow-simulation-to-a-rotating-propeller), I understood how to determine the velocity (V) of the air flow for a angular velocity ω of the propeller.

But is there a way to get the relation V=f(ω) ?

Thank you ! :)

Sorry for my mistakes, I'm not anglophone, I hope you'll understand me

### 2 Answers

Hi Bakeneko83:

The propeller does not induce a single speed, but a speeds vectorial field, which components modulus, and directions, (axial, tangencial and radial) change around the impeller.

Anyway a kind of rough averaged speed could be calculated from the propeller thrust obtained from your CFD.

If it is supposed that mass "flow IN" the propeller disk, equals mass "flow OUT"(not true, but useful), the fluid momentum change, can be assumed to be only due to the fluid speed change in the axial direction.

As Thrust is equal to momentum change, speed change can be calculated.

From a similar path, and from the propeller Torque obtained from your CFD, radial fluid speed can be calculated.

As an addon, flow induction factors can be calculated as well.

Regards