Wind turbine blades represent approximately 15 to 20% of the total cost of the wind turbine. At present, the blades of large wind turbines are mainly made of composite materials, and the content of composite materials generally exceeds 80%. According to statistics, every 6% increase in the size of a wind turbine's blades can increase the amount of wind energy captured by 12%. The original intention of the blade design is to achieve a balance between dynamic efficiency and structural design. The choice of materials and processes determines the actual final thickness and cost of the blade. Structural designers play an important role in how to combine design principles and manufacturing processes, and must find the optimal solution between ensuring performance and reducing costs. Blade force analysis: Pushing on the blade causes the blade to rotate. The distribution of thrust nis not uniform but proportional to the length of the blade. The thrust force experienced by the tip of the blade is greater than that of the blade root. Beam design: The bending deformation caused by the self-weight of the blade and external thrust constitutes the main load of the blade. In order to improve bending performance, unidirectional fiber cloth is used along the length direction of the blade, as well as the upper and lower beams. the caps are connected by a shear web in the middle Separated as much as possible, the shear webs are made of bidirectional fiber fabric and foam (PET) cores laid diagonally to increase overall stiffness. Internal beam structure: In order to reduce production costs, some unnecessary materials can be removed from the design. Common blades adopt a hollow design. Foil Wrap: The Main Function of the Wrape of sheet is to provide an aerodynamic shape. The sandwich structure of the sheet shell increases rigidity. The sandwich structure is composed of a fiberglass surface layer with a foam core material (PET) or a balsa wood core material (BALTEK) in the middle. The sandwich structure is rigid enough to support bending loads while preventing debonding. The fibers distributed diagonally in the housing provide the necessary torsional rigidity. Blade Root Design: The blade root portion is usually designed to be round. At the same time, in order to meet maintenance and other needs, the blade roots are often connected by bolts to facilitate disassembly and assembly. Welded flange connections can be used for metal beams. Geometric size optimization design: without changing the geometric shape of the blade, the performance of the bladee can be changed by adjusting the thickness of the spar cap and the production cost can be reduced. Thinner blades require thicker spars, which increases production costs. At the same time, the strength of the strip must be increased, but as the thickness becomes thinner, the total material consumption does not change significantly. In summary, optimal design of geometric dimensions requires careful consideration of many aspects such as fan design, load analysis, structural design and manufacturing cost to achieve the best results.
Actually, there are single-blade and two-blade wind turbines. But the most common number of blades in modern wind turbines is three, the result of compromises between various aspects and parameters during the design process. These aspects include, but are not limited to: aerodynamics, con efficiencyenergy version, manufacturing and maintenance costs, system reliability, noise and aesthetics.
From a simple analysis of the technical parameters, a larger number of blades can:
(1) Increase the mechanical torque
(2) Increase power output;
But a greater number of blades will also:
(3) Reduce the maximum rotation speed;
(4) Bring a heavier system. The cost is increased and the maintenance is more complicated and difficult.
Therefore, motors with a large number of blades are more suitable for operation in low-speed locations, such as water pumps and grain grinding motors.
Wind turbines expect the blades to spin at a relatively high speed, so the size of the generator located in the center of the blades (at the top of the tower) does not need to be large to meet the frequency. grid requirements.
Additionally, wind speeds generally increase at higher altitudes. As the wind turbine tower is very high, the blades are also very long (40m-60m*). There is a significant difference in wind speed between blades rotating to a high position and blades rotating to a low position.
If the generator has only two blades, then when the blades rotate to a high position and a low position, the force exerted on them is obviously not uniform enough, so a tower must be designed stronger and more stable. to hold it in place. Generator and blades. The three-blade generator can alleviate this imbalance to some extent, making it run more smoothly. Smooth means less noise and less wear.
The efficiency of wind turbines in absorbing energy from wind speed is related to the tip speed ratio. A certain top speed ratio must be maintained to achieve uhigher efficiency. As for the engine, it is already quite efficient and is not the center of attention.
In order to maintain the peak speed ratio, the rotational speed must change in direct proportion to the wind speed. To put it bluntly, it needs to be sometimes faster and sometimes slower. It doesn't matter if it's slow, but it spins fast and dies quickly, so I hope the resistance of the single chip will be higher, so the single chip will have to be wider. The choice is therefore limited to one, two or three pieces. The single coin is unbalanced, while the double coin is theoretically balanced. However, it is difficult to actually make, so we have to choose three parts, which is an economical and feasible compromise.