wind turbne blades?

Question

i am making a wind turbine, tomorow i have to make the rotor blades, does anyone know the degree of angle needed to turn the alternator, i've done lots of research into wind turbines but theres not much info on the rotor blades, this will be a mk11 version as i have made one before, the one i made before had soil pipe rotor blades but these were not powerfull enough to turn the turbine whilst connected to an alternater,although it turnedthe shaft etc without the alternater connected

Answer 1

hard one to answer, but let me give it a shot.

1) start with a low reynolds # airfoil section. maybe a selig airfoil.

2) determine the ammount of torque you need to turn your shaft.

3) use a lifting line theory to determine your starting AOA (angle of attack), taper, legnth, and twist to acheive the ammount of lift to produce the determined torque.

4) if you do not have a jig to build the blades, then i would recommend using a 3 blade design so you wont have to worry about extreme vibration. just make sure the blades are fairly equal in mass.

good luck

Answer 2

Just as an experiment I carved a 36" solid maple propeller and with a custom machined hub attached it to a 65 amp GM automotive alternator. the prop blank was 1 1/2 x 3 1/2. I used a modified Clark Y airfoil section with a 5 degree angle of attack at the tip graduating to a 20 degree near the hub. Look at a model airplane propeller to get the general idea. If your good and the cross sections are equal it should be pretty easy to balance.

On a 20 ft tower this thing put out the full 65 amps in a 50 mph wind, at an rpm of 4500 (checked with strobe). That works out to a tad over 800 watts output for a 36" dimeter prop in a 50 mph wind. (tip: The flat side goes into the wind on wind turbines)

The alterntor was trash in 3 months because it 's bearings can not stand the thrust forces...just for info.

Answer 3

Turbine blades are carefully designed like aircraft propellers. The angle changes the further out you get so you get a twist. You get a sharp angle near the centre and a much lower angle at the tips.

If you don't have a properly shaped blade you make a windmill instead of a wind turbine.

Windmills work on drag and have lots of torque. Turbines work on lift and have lots of speed and this is what you want for efficiency.

Answer 4

To convert CFM to thrust, you need to know the velocity and cross-sectional area of the airstream.


F = M * a

F: force or thrust (newtons)

M: mass (kilograms)

a: acceleration = dv/dt
v: units of meters per second
a: units of meters per second per second


Metric and english unit conversion:

1 m/s = 2.24 mph
1 cubic meter = 35.31 cubic feet
1 cubic meter/sec = 2119 CFM (cubic feet / minute)


At atmospheric pressure and room temp, the density of air is approximately 1 kg/cubic meter, a handy number.
On earth, the acceleration of gravity is 9.8 m/s2, so 1 kg weighs 9.8 newtons. F (newtons) = m (kg) * a (m/s2).

If a fan accelerates 1 cubic meter of air (mass=1 kg) to a uniform velocity of 10 meters per second (22 mph) in 1 second,
it must have a thrust of F = m * a = (1 kg) * (10 m/s per second) = 10 newtons, which is roughly 1 kg or 2.2 pounds.
If the velocity is uniform across the flow, that volume and velocity implies a cross-sectional area of 0.1 square meter,
for example a circle 36 cm in diameter. Note that the fan described in the letters above did not quite reach a 10 m/sec
air velocity.

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Rather than F = M*a, a physicist might prefer to write: F = dp/dt

where p (should be Greek 'rho') is momentum, and dp/dt is the rate of change of momentum with time.

p = m*v so dp/dt = d/dt (m*v) = m(dv/dt) + v(dm/dt).

If the mass does not change with time (dm/dt=0) this becomes just F=ma.