Patent Application
20100143135
1. Technical Field
The subject matter described here generally relates to fluid reaction surfaces with specific blade structures that are formed with a main spar, and, more particularly, to torsion loading for wind turbine blades.
2. Related Art
A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator or wind power plant.
Wind turbines are typically categorized according to the vertical or horizontal axis about which the blades rotate. One so-called horizontal-axis wind generator is schematically illustrated in
The blades 10 generate lift and capture momentum from moving air that is them imparted to the rotor as the blades spin in the “rotor plane.” Each blade 10 is typically secured to the hub 9 at its “root” end, and then “spans” radially “outboard” to a free, “tip” end. The front, or “leading edge,” of the blade 10 connects the forward-most points of the blade that first contact the air. The rear, or “trailing edge,”of the blade 10 is where airflow that has been separated by the leading edge rejoins after passing over the suction and pressure surfaces of the blade. A “chord line” connects the leading and trailing edges of the blade in the direction of the typical airflow across the blade. The length of the chord line is simply the “chord.” The shape of the blade 10, when viewed perpendicular to the direction of flow, is called the “planform.” The thickness of a blade 10 typically varies across the planform and chord.
The blades 10 are typically fabricated by securing various “shell” and/or “rib” portions to one or more “spar” members extending spanwise along the inside of the blade for carrying most of the weight and aerodynamic forces on the blade. Spars are typically configured as I-shaped beams having a web, referred to as a “shear web,” extending between two flanges, referred to as “caps” or “spar caps,” that are secured to the inside of the suction and pressure surfaces of the blade. However, other spar configurations may also be used including, but not limited to “C-,” “D-,” “L-,” “T-,” “X-,” “K-,” and/or box-shaped beams. The shear web may also be utilized without caps.
“Angle of attack” is a term that is used in to describe the angle between the chord line of the blade 10 and the vector representing the relative motion between the blade and the air. “Pitching” refers to rotating the angle of attack of the entire blade 10 along the spanwise axis into or out of the wind in order to control the rotational speed and/or absorption of power from the wind. For example, pitching the blade “towards feather” rotates of the leading edge of the blade 10 into the wind, while pitching the blades “towards stall” rotates the leading edge of the blade out of the wind.
Since the speed of the blades 10 relative to air increases along the span of the rotating blades, the shape of the blades is typically twisted in order to maintain a generally consistent angle of attack at most points along the span of the blade. However, such fixed twist angles are generally optimized for only one set of operating parameters for the wind turbine 2.
These and other drawbacks associated with such conventional approaches are addressed here in by providing, in various embodiments, a torsionally loadable wind turbine blade, including a loading member secured to a body of the wind turbine blade; and an adjuster for actively displacing the loading member and torsionally deforming the blade on a spanwise axis.
Various aspects of this technology will now be described with reference to the following figures (“FIGs.”) which are not necessarily drawn to scale, but use the same reference numerals to designate corresponding parts throughout each of the several views.
The blade 20 includes one or more loading member(s) 22 secured at one or more locations of a body of the wind turbine blade 20. For example, as illustrated in
In various embodiments, the loading member 22 may be as stiff as possible along its loaded axis and as flexible as possible along the bending axis so that it does not interfere with the bending deformation of the blade 10. For example, the flexibility may be elastic in a linear or non-linear configuration. The loading member 22 may also be arranged in such a way that the spar cap is torsionally loaded.
As illustrated in the schematic cross-sectional view of the spar 24 shown in
Other arrangements for the cable 28 may also be provided. For example, as illustrated for the I-shaped spar 24 in
Multiple loading members 22 and adjusters 26 may be provided in different sections of the blade 20. For example, since the blade 20 is relatively stiff near the root as compared to at the tip, torsional loads may be concentrated in areas that have a lower than average stiffness in order to achieve maximum deformation. Alternatively, or in addition, as illustrated in
For example, it is expected that the technology described above will provide a typical forty-meter blade 10 available from General Electric Corporation with a roughly exponentially increasing torsional deformation D, in degrees, along the length of the span L, in meters, as shown in
The technology described above offers various advantages over conventional approaches. It allows the blade 20 to be torsionally deformed so that the angle of attack for a given pitch at off-design wind speeds is closer to an optimum value. The optimum angle of attack over the blade length may then be obtained at a wider range of wind speeds. Energy capture can therefore be enhanced.
It should be emphasized that the embodiments described above, and particularly any “preferred” embodiments, are merely examples of various implementations that have been set forth here to provide a clear understanding of various aspects of this technology. One of ordinary skill will be able to alter many of these embodiments without substantially departing from scope of protection defined solely by the proper construction of the following claims.
