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Optimization of Turbine Blades 

In order to obtain the maximum energy from the wind turbine, it should be to improve the efficiency of the wind turbine by optimizing the design of the blades



The principle of a blade


The blades of a wind turbine work on exactly the same principle as the wings of an airplane as explained by the diagram below. Thanks to the shape of the profile the passing air on the top of the wing, the upper surface must travel more path than the one passing below, the lower surface, this is why the air accelerates creating depression and therefore an aspiration to the top. On the lower surface, the air causes an overpressure which also generates a force towards the high. These two efforts together are called lift. The penetration into the air is not done not without friction another effort, the drag opposes the motion.
The aerodynamic result is the result of these two efforts, the lift and the drag, it is what allows the plane to hold in the air or here to rotate the rotor.

Development of airfoils


Among the relatively recent developments in profile design, the family of thin profiles introduced by Tangler from the solar energy resources institute (SERI) from Colorado. These blades have been described by Davidson as « the blades of the future », who claim that these blades can produce 31% more power than Danish blades traditional. The SERI S897 profile is an example of this family.

Another example of modern profiles is SG profiles, recently developed by Professors: Michael Selig (S) and Phillipe Giguere (G) from the University of Illinois (USA).
These profiles are specially designed for small wind turbines, they are probably the only profiles designed specifically for this task.

The use of NACA profiles (US National Advisory Committee on Aerodynamics) of NASA, in the wind field, is still very popular.
The old series of NACA23xxx profiles, used for a long time for the blades of wind turbines, is currently abandoned since this profile loses these qualities aerodynamics (considerable drop in its C l, max) when its surface becomes rigorous with the deposit of impurities (insects, dust, etc.)

This same problem was also observed when using the NACA 44xxx series but to a lesser degree.
In an effort to resolve this problem of sensitivity of C l, max to roughness, manufacturers are
being turned to the families of profiles NACA63xxx and LS-1. These profiles carried a
solution to this problem. 

The NACA63xxx profile is widely used in the design of modern blades, this type of profile
has shown excellent properties when used in wind turbines.
Nevertheless, some improvements were necessary, because of one of the challenges in the design of
profiles for wind turbines is to develop profiles, suitable for the indoor area blades, having a thickness large enough to withstand the high stresses applied in the vicinity of the installation, while maintaining a high lift coefficient.

Examples of thick profiles designed for this reason include the NACA63-621 profile,
profile LS1-421 and profile S897.

These thick blades are better suited for the area interior because this thickness makes the blade more resistant and will allow a transition progressive geometric (from the embedding where the section is circular towards the profile aerodynamic).

The profiles characterized by a C l, max quite low, represent a drawback when they are used in the inner area of ​​the blade (towards the embedding) because they reduce the efficiency energetically.
But this aspect turns out to be advantageous in the outer area of ​​the blade (towards the
tip) because it limits excess power, which poses a risk to the structure.

For profiles characterized by a high C l, max, the problem is completely reversed. This
type of profile is advantageous in the inner area of ​​the rotor, however, it represents a
the downside in the outdoor area.

To avoid these drawbacks, some blades have been designed with different profiles in
each area. In the intermediate zone, the profile changes shape gradually in order to
allow the passage from one profile to another.

It is obvious that despite these new features in the design of the profiles, improvements
can always be brought.

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