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Calculating Drag Force due to air on a Pedestal Fan blade

  1. Nov 10, 2011 #1
    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.
     
  2. jcsd
  3. Nov 10, 2011 #2

    russ_watters

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    Staff: Mentor

    Welcome to PF!

    Why don't you just measure the electrical input to the fan?
     
  4. Nov 11, 2011 #3
    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.
     
  5. Nov 12, 2011 #4
    Any idea about drag force, Russ?
     
  6. Nov 12, 2011 #5

    russ_watters

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    Staff: Mentor

    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.
     
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