Livre Power, Lda.

Outubro 12 2010

Aerodynamics is of great importance in the design and level of benefits from a wind turbine. Let us first introduce some basic concepts of aerodynamics that are applied in construction of wind turbines.

 

Aerodynamics is the branch of fluid mechanics that studies the movement of air around the body.
The shape and position of an object determine its resistance to the passage of air.

 

A flat surface, placed perpendicular to wind direction, suffers a high strength, since the air strikes with it and there are great turbulence.


The round objects do not present much resistance because the air flowing by following its contour.
Still to generate vortex, eddies, areas of air outlet, which creates resistance and slows the air, as shown in the video:

 


The poles of the turbines create zones of decompression, or low pressure, opposite to the direction of the wind, causing the formation of vortex, eddies, causing oscillating movement of the structure and decrease the wind speed before the pole .


This causes the shovel passes, at one point along the pole receives less energy from the wind than the others.


The aerodynamic resistance, which measures the strength of opposition to the passage of air in a given area increases the larger the area facing towards the wind. Therefore it is of any interest that the profile of the blades and the main body of the horizontal axis wind turbines is as slim as possible. See the second video that shows the formation of eddies when the profile has a greater thickness.

 

Contrary to what many think, beaked forms are not very aerodynamic when they attack the air from the front, easily generate vortex, as can be seen in the third video.


 

They are better at points of exit or escape of air.


The air wraps best

in collision with surfaces smooth curves and rounded, or spindle-shaped tip of a bullet.

This must be the way to give the "nose" of the rotor, which are connected wind turbine blades.

 

The forms are said to be streamlined while minimizing the resistance of air flow and deflect produce little turbulence. They allow a high rate of air flow.

 

According to Bernoulli's theorem, when increasing the speed of an air stream, for an area, decrease the pressure that air exerts on it.

Applying this principle to the profile of a blade of a windmill, when she has a proper angle of attack, thereby generating greater pressure on the lower surface, where the air has a lower speed, while the upper surface of the air gets more speed by having to travel a greater distance, creating a pressure difference which results in a lift with a vertical direction from bottom to top, as with an airplane wing.


Profiles with greater curvature produce more support, yet have higher drag, why not encourage high speeds.

 


The profiles are almost symmetrical most streamlined, allowing higher speeds in the flow of air, so they are faster.

 

Since the end of the blade has a round larger than a point closer to the center of the rotor, then the ideal is that the profile of the tip is nearly symmetrical, with thin and short. The nearer the center of the rotor, the profile gets more curvature, thickness and length.

For the same reason the difference in speed, angle of attack must also vary. Near the center is larger and goes down as we approach the end. If we increase the angle of attack very lost support, we generate a stall, as shown in the video above left.


The aerodynamic resistance is smaller at the tip to allow greater speed, increasing toward the center of the rotor.

 


In the end, despite the profile is nearly symmetrical, it will generate a lift force produced in the zones near the vicinity of the center of the rotor, this is due to the higher speed. This feature optimizes the use of wind energy by improving the speed of the alternator.


Choosing the ideal angle of attack varies depending on the configuration profile and used the paddle. But in most cases, are the angles of attack lower than give higher speeds.

 

Aerodynamic aspects are damaged with obstacles, buildings, trees, hills, etc.. near the windmill, for disrupting the smooth operation because they generate vortex destabilize the direction and wind speed, reducing your income.

Finally, as mentioned in previous reviews, the sound of the wind turbine varies in direct proportion to wind speed and inversely with the quality of wind turbine aerodynamics. As we do not control the wind speed, we can do is to improve the aerodynamics, essentially, spades, because these are the primary responsibility of the noise. The matter does not end here, he'll be back another time.

Arménio Carreira às 06:49

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