Реферат: Wind Power Essay Research Paper The wind

direction of the aerofoils, the tail rotates a shaft, which rotates the

whole windmill in the proper direction so as to orient it towards the

wind. As Paul Gipe explained in his book Wind Energy comes of age, (page

27), Wind gusts can greatly affect a windmill. A turbulent gust is a gust

greater than two minutes with a certain mean wind speed. Gusts are

analyzed extensively, with magnitudes, one fo r the lull speed, which is

the wind speed of a negative gust amplitude, and the peak speed, which is

the wind speed for a positive gust amplitude. The gust amplitude is the

difference between the largest speed in the gust and the mean speed. The

gust du ration is the time from the beginning to the end of a gust. The

gust frequency is the number of positive gusts, which occur per unit time.

The gust formation time is the time it takes from the beginning of a gust

to the time it attains the peak gust spe ed. The gust decay time is the

time it takes for the gust the end after it reaches its highest amplitude.

There is quite a bit of terminology with aerofoils. The angle of the

surface to the fluid flow is the angle of attack, alpha. The angle of

attack must be just right. If it is too great, the lift will dramatically

decrease and the drag will increase, st alling the windmill. At rest,

(when the windmill is not in operation), the angle of attack is 85?. When

in motion, the angle of attack is anywhere from 2-10 degrees. Newer and

more advanced windmills have an angle of attack in the upper end of this

ran ge. The pitch angle, ? is the angle between the chord of the aerofoil

and its plane of rotation. The pitch angle can be adjusted. Solidity is

the ratio of the blade width (at widest point) to the distance between the

centers of the blades. A typical “pinwh eel American windmill” might have

a ratio of about 1:1, because the blades are very narrow and very close

together, whereas a new two-bladed aerofoil would have a ratio of about

0.03. There is a transfer of work between the wind stream and the moving

blade. In order for this transfer to be efficient, a typical blade is