Calculating Drag Force due to air on a Pedestal Fan blade

Kaycee92

I am doing a project where in a pedestal fan is alternatively powered using a flywheel. The flywheel is brought to some initial angular velocity by the electric motor. Now, if the power goes off, the fan blades would be coupled to the flywheel and it continues to rotate for the next 10 minutes.

After the power goes off, we have considered that

Energy-flywheel + Energy-fan = ∫ (Torque-drag force * ω -fan) dt

I'm having trouble calculating the torque due to the drag force and how to geometrically simplify the fan blades.

Any solution would be very much helpful.

russ_watters

Welcome to PF!

Why don't you just measure the electrical input to the fan?

Kaycee92

Yes, but that would give me the power consumed at some constant fan speed( during operation).

When my flywheel is engaged, the rpm keeps on reducing and is a function of time.

If I know how the drag force is related to angular velocity and how much torque is generated, I would then be able to solve.

Kaycee92

Any idea about drag force, Russ?

russ_watters

Well, once you have the peak, you can use the fan affinity laws to calculate the power at any rpm. Basically, power is a cube function of rpm.