Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculate torque for a wind turbine

  1. Apr 24, 2012 #1
    density=1.2041 kg/m^3
    Power 1.65 MW
    Rotor radius (blade length) = 37m
    calculated swept area = 4,301 m^2
    wind speed 12m/s

    the rotor speed range is upto 20rpm

    i want to calculate the torque but not quite sure how to go about it

    Thanks for any help!
     
  2. jcsd
  3. Apr 25, 2012 #2

    rock.freak667

    User Avatar
    Homework Helper

    You can always use Power = Torque*angular velocity.
     
  4. Apr 26, 2012 #3
    An important piece of information is that the velocity of a blade tip of a 3 blade rotor in a 12 m/s wind is about 60 m/s. This is because the tip-speed ratio equals velocity of blade tip/ velocity of wind. The tip-speed ratio for a 3 blade rotor is about 5, wind speed is 12 m/s.

    You know the radius of the blade so you know the angular velocity, ω=V/r. Make sure ω
    is less than 20 rpm.

    As noted above power in the wind=τ*ω, the power in the wind is not 1.65 MW that is the rotor power you need to find the Power in the wind=rotor power/efficiency of turbine

    You can find the efficiency of turbine(η) because rotor power=η*(.5*A*ρ*v^3)

    η=rotor power/power in wind. η accounts for all the losses in generator, transmission etc.

    Now you know power in the wind and ω so you can find Torque (τ)
     
  5. Apr 26, 2012 #4
    Thanks a lot for the quick reply
    I've done it this way:

    We know the rotor is rated up to 20RPM hence so to change it to angular velocity we;
    (20*2π)/60=2π/3

    We also know P=τω 1.65MW= τ * 2π/3 τ=7.878×〖10〗^5


    I've already done this before: (P=1.65mw)
    Cp(η) = Rated power/Power = P/(½ρAv3) = 0.369 = 37%
    (Power = ½ρAv3 = 4.47MW)

    Again thanks a lot for the help :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook