[Lucky Luka]

Hi all
I'm tryng to simulate the behaviour of an axial fan using a rotating reference frames applied to it.
I know its rotating speed.
I can obtain from the simulation its pressure drop between its inlet and its outlet.
I computed in a report its power multiplying the pressure drop [Pa] by its flow rate [m3/s].
I've been told that I can even obtain this power value considering the rotating flow of the fluid (air).
How can I do that? I have no idea.

Thanks


Luka

[fluid23]

Axial fan power can be expressed as torque x angular velocity (tau x omega). Tau and omega should always be expressed in fundamental units, so N-m and rad/sec, or lbf-ft and rad/sec. Typically, you would use that expression to find the power of the fan and not the power input to the fluid. Fan efficiency will result in some losses.

However, we know that every action has an equal and opposite reaction, therefore, you can extend that relationship to find the power input to the fluid by multiplying the torque of the air in the fan region by its bulk angular velocity. Personally, I think mass flow x induced velocity is a much more succinct measure of this, however, if you want to check it you can do as follows:

Create a derived part > threshold which includes all the cells in your fan region. Then setup a moment report using your threshold then a report of mass flow averaged angular velocity. Verify units, then combine the two into an expression report $torqueReport*$speedReport. That should give you your power input to the fluid.

Keep in mind that the two answers (mdot x V and tau x omega) will probably not agree perfectly. Mdot x v likely being the more accurate of the two.