[0001] High Efficiency Wind Turbine Blade System

Cross-Reference to Related Applications

[0002] The present patent application claims the benefits of priority of commonly assigned U.K. Patent Application No. 0905881.9, entitled "High Efficiency Turbine Blade System" and filed at the United Kingdom Intellectual Property Office on April 4, 2009, the content of which is incorporated herein by reference.

Field of the Invention

[0003] The present invention generally relates to wind turbines and wind turbine blades. Without loss of generality, the present invention particularly relates to horizontal axis wind turbines and wind turbine blades therefor.

Background of the Invention

[0004] Wind turbine blade systems are known in the art and are useful in producing the rotational torque required by wind turbines equipped with an electrical power generator to generate electrical energy out of wind power. Typical horizontal axis wind turbines of the prior art generally consist of a nacelle or a stationary hub portion fastened at a distal end of a support structure, and a horizontal axis wind turbine rotor assembly provided with a plurality of radially projecting turbine blades. The stationary hub portion typically conceals an electrical power generator having a rotatable power input transmission shaft engaged with the wind turbine rotor assembly. In some models of wind turbine, the central hub of the rotor assembly may also conceals a mechanism that allows the wind blades to twist about their longitudinal axes so that the angle of twist, or pitch angle, may be optimized as a function of wind speed. Some models of wind turbines may also include an outer rim or shroud connecting the end or outer tips of the blades. [0005] Some wind turbine blades of the prior art have an airplane wing-like shape and cross-section, and are radially connected about the central hub of the turbine rotor at a generally incident angle relative to the rotational axis of the rotor such that an airplane wing-like effect is achieved. Thus, when an airflow is directed toward the upwind end of the turbine rotor, an higher air pressure system is created proximally the lightly concave lower airfoil surface of each blade, while a lower air pressure system is created proximally the substantially convex upper airfoil surface thereof which, in turn, generates lift and induces a rotation movement to the turbine rotor.

[0006] It is well known in the art that minimum wind speed conditions are required to properly operate a conventional wind turbine since, when relatively low wind speed conditions prevail, there are losses in output torque due to an air turbulence system that is created and which substantially impairs the lower air pressure system near the upper airfoil surface of each turbine blade. This air turbulence also generates relatively high noise levels.

[0007] Exemplary prior art wind turbine rotors are illustrated in U.S. Patent Nos.

2,137,559 (Algee), 5,599,172 (McCabe), 5,910,688 (Li), 7,550,864 (Anderson et al.) and in U.S. Patent Application Publication No. 2008/0093860 (Suzuki).

[0008] While these prior art devices generally include a wind turbine blade system that contributes to produce electrical energy out of wind power, they also entail one or more of the following disadvantages:

[0009] a) they generally require relatively high wind speed conditions in order to generate enough rotational torque to operate properly the electrical power generator concealed in the stationary hub;

[0010] b) they typically generate significant noise levels, even when operating at their minimum operational wind speed.

[0011] Against this background, there exists a need for a new and improved horizontal axis wind turbine blade system that avoids or mitigates the aforementioned disadvantages. Summary of the Invention

[0012] It is a general object of the present invention to provide a new and improved wind turbine blade system. According to a preferred embodiment of the present invention, the wind turbine blade system generally comprises a plurality of equidistantly, radially projecting alike blades. As in conventional wind turbine applications, the base of the blades is adapted to be connected to the central hub of a wind turbine rotor. In some wind turbine applications, an outer rim may also connect the end or outer tips of the blades.

[0013] Also, as in conventional wind turbine applications, the turbine blades are suitably sized and shaped, as well as suitably disposed at a generally incident angle relative to the rotational axis of the turbine rotor such that an airplane wing-like effect is achieved when an airflow is directed toward the upwind end of the turbine rotor, which in turn induces a rotation movement to the latter.

[0014] The turbine blades are further characterized in that they are radially-disposed about the central hub of the turbine rotor such that a portion of a first blade, near its base end thereof, overlaps a portion of the adjacent blade, near the base end of the latter. The thus cascading overlapping arrangement of the blades about the central hub of the rotor forces a portion of the higher air pressure system created proximal the lower airfoil surface of the adjacent blade to be redirected toward the upper airfoil surface of the first blade. Hence, the air turbulence normally created proximally the upper airfoil surface of each blade is significantly minimized which, in turn, proportionally improves the lower air pressure system proximal the upper airfoil surface of each blade.

[0015] The result is a turbine blade system generating an increased torque output at low wind speed, as well as lower sound emitting characteristics during operation due to the consequently minimized air turbulence near each turbine blade.

[0016] The turbine blades may be advantageously manufactured, for example, as a polyester shell, using a rotational moulding process, and injected with high density polyurethane. [0017] The main advantages of the present invention is a wind turbine blade system: [0018] a) whose configuration and assembly allow for a wind turbine rotor that can generate an increased torque output at relatively low wind speeds compared to comparably sized wind turbine rotors of the prior art;

[0019] b) which is also relatively quieter during operation.

[0020] Other and further aspects, features and advantages of the present invention will be obvious upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice. The features of the present invention which are believed to be novel are set forth with particularity in the appended claims.

Brief Description of the Drawings

[0021] The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which: [0022] Figure 1 is a front, or upwind elevation view of an exemplary implementation of the turbine blade system incorporating the principles of the present invention mounted within a horizontal axis, wind turbine rotor assembly;

[0023] Figures 2A to 2D respectively show a plan view of the lower airfoil surface of an exemplary wind turbine blade, a tip end perspective view thereof, a base end plan view thereof, and a plan view of the upper airfoil surface thereof;

[0024] Figure 3 is a front, or upwind elevation view of the turbine blade system of the wind turbine rotor of Fig. 1, here shown without the central hub and the outer rim;

[0025] Figure 4 is a side elevation view of the turbine blade system of Fig. 3;

[0026] Figure 5 is a partial front, or upwind elevation view of the turbine blade system of Fig. 3, in which only three turbine blades are shown for clarity;

[0027] Figure 6 is a side elevational view of the partially shown turbine blade system of Fig. 5.

[0028] Figure 7 is a side elevation view of an exemplary wind turbine incorporating the principles of the present invention. Detailed Description of the Preferred Embodiment

[0029] A novel wind turbine blade system will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

[0030] Fig. 1 shows a wind turbine blade system 10 according to the present invention that is mounted within a typical wind turbine rotor 12. The wind turbine rotor 12 generally comprises a central hub 14 from which are radially extending a plurality of turbine blades 16, and an outer rim 18 connecting the distal tip ends 20 of the blades 16.

[0031] The base ends 22 and tip ends 20 of the turbine blades 16 are preferably adapted to be fixedly connected to an outer peripheral portion 15 of central hub 14 and an inner peripheral portion 19 of outer rim 18 respectively. Although the turbine blades 16 are herein described as being fixedly connected to their respective peripheral portions of central hub 14 and outer rim 18, it is to be understood that, in alternate embodiments of the wind turbine rotor 12, each turbine blade 16 may have its base end 22 and tip end 20 axially pivotally connected to their respective peripheral portions of central hub 14 and outer rim 18. In cooperative relation with any suitable conventional mechanism typically concealed in the central hub 14 of the wind turbine rotor 12, the blades 16 may be twisted about their longitudinal axis 21 so that the angle of twist, or pitch angle, may be optimized as a function of wind speed, or be used as a breaking or stalling means against the rotation of the turbine rotor 12.

[0032] Figs. 2A to 2C show various views of a preferred embodiment of the wind turbine blade 16 in accordance with the principles of the present invention. Fig. 2 A shows a plan view of the lower airfoil surface 36 of the turbine blade 16 having a substantially trapezoidal shape that is generally defined by oppositely disposed longitudinal leading edge 26 and trailing edge 28, and by oppositely disposed base end 22 and tip end 20. Notably, the tip end 20 is narrower than the base end 22 when the blade 16 is viewed as in Fig. 2A. [0033] The leading edge 26 and trailing edge 28 of the wind turbine blade 16 are both defining lightly curvilinear edges that respectively project forwardly and rearwardly such that the turbine blade 16 reaches a maximum width 25 dimension at roughly one third of its length 23 relative to the base end 22. As can be observed in Fig. 2A, the trailing edge 28 defines a relatively more pronounced outwardly extending curvilinear edge compared to the leading edge 26, which provides the blade 16 with an extended rear surface portion 30 towards the trailing edge 28, relative to a generally centered longitudinal axis 21 of the blade 16, as compared to an extended front or forward surface portion 32 generally defined by the leading edge 26. The purpose of the rearwardly extending surface portion 30 will be described more below.

[0034] The curvilinear leading edge 26 and trailing edge 28 thus render the distal portions near the base end 22 and the tip end 20 of the blade 16 substantially taper- shaped, as best illustrated in Fig. 2A.

[0035] Figs. 2B and 2C further show the wind turbine blade 16 having a substantially tear-drop shaped cross-section, as illustrated through the general shapes of the base end 22 and tip end 20 of the blade 16. Thus, substantially all along the longitudinal axis 21 of the turbine blade 16, the latter has a cross-section that closely resembles the cross-section of a conventional airplane wing, with a substantially convex upper airfoil surface 34 and a relatively lightly concave lower airfoil surface 36.

[0036] Furthermore, Fig. 2C shows that the trailing edge 28 of the turbine blade 16 defines a continuous longitudinal curvature corresponding to an angle varying from about zero degree, near the base end 22, to about twenty degrees, near the tip end 20, relative to the leading edge 26 of the blade 16 taken as a reference point. Thus, the wind turbine blade 16 displays a light continuous longitudinal curvature with respect to its central axis 21 that closely resembles the longitudinal curvature, or twist, of a typical propeller blade of a small airplane. It is to be noted that the continuous longitudinal curvature of the trailing edge 28, relative to the leading edge 26, may define any other suitable angle difference comprised between about zero degree and up to about forty degrees. [0037] In a preferred assembly configuration of the turbine blade system 10, within a wind turbine rotor 12 such as the one illustrated in Fig. 1, each wind turbine blade 16 is generally oriented at an incidence angle relative to the general horizontal axis 13 (see Fig. 4) of the turbine rotor 12, with the lower airfoil surface 36 of the blade 16 generally oriented at an angle towards the upwind, or front end 40 of the turbine rotor 12 and, inversely, with the upper airfoil surface 34 of the blade 16 generally oriented at an angle towards the downwind, or rear end 42 of the turbine rotor 12, as best illustrated in Fig. 4.

[0038] Furthermore, as best illustrated in Figs. 5 and 6, each wind turbine blade 16 is disposed about the central hub 14 of a turbine rotor 12 such that part of the rear surface portion 30 of the lower airfoil surface 36 of a first blade 16a, near its trailing edge 28 thereof, is substantially overlapped by part of the front surface portion 32 of the upper airfoil surface 34 proximal the leading edge 26 of a preceding turbine blade 16b, as observed from the upwind end 40 of the turbine rotor 12.

[0039] In operation, as is the case with conventional airplane wings, when an airflow is generally directed towards the upwind end 40 of the turbine rotor 12, in a generally parallel orientation along the rotational axis 13 of the latter, the thus incident oriented and relatively wide lower and upper airfoil surfaces 34, 36 of the blades 16, combined with the airplane wing-like cross-section of the latter, create an higher air pressure system proximally the lower airfoil surface 36, and a lower air pressure system proximally the substantially convex upper airfoil surface 34. Hence, as the airflow flows around the blades 16, an airlift effect is created which, in turn, induces a clockwise rotation movement to the wind turbine rotor 12 when observed from the upwind end 40 of the latter (e.g. as shown by the curved arrow in Fig. 1).

[0040] As illustrated in Fig. 6, additionally to the airlift effect created by the airplane- wing-like shape of the turbine blades 16, a portion 50 of the higher air pressure system created proximally the lower airfoil surface 36 of a first turbine blade 16a is redirected by its exceeding rear surface portion 30 toward the upper airfoil surface 34 of the preceding turbine blade 16b. With an increased airflow speed thus created proximally the upper airfoil surface 34 of each wind turbine blade 16, the air turbulence normally created thereabout is significantly minimized which, in turn, improves the lower air pressure system proximally the upper airfoil surfaces 34 of the blades 16 and thereby increases the airlift effect. Hence, the turbine blade system 10 may achieve an increased torque output in relatively lower wind speed conditions, compared to comparably sized turbine blade systems of the prior art. Additionally, due to the minimized air turbulence created proximal the upper airfoil surfaces 34 of wind the turbine blades 16, lower sound emitting characteristics are also achieved during operation.

[0041] It is to be noted that the number and size of the wind turbine blades 16, additionally to their incident angle relative to the rotational axis 13 of the wind turbine rotor 12, can be varied to maximize the efficiency of the latter depending on the average wind conditions of the area.

[0042] The blades 16 of the turbine blade system 10 described above are preferably constructed of durable corrosion resistant materials. For example, the wind turbine blades 16 may be advantageously manufactured as a polyester shell, using a rotational moulding process, and injected with high density polyurethane. Of course, any other suitable rigid material, or combination of materials, may be used in the conception of each wind turbine blade 16; the present invention is not so limited.

[0043] Referring now to Fig. 7, in use, the wind turbine rotor 12 comprising the wind turbine blade system 10 is typically rotatably mounted, via its hub 14, to the nacelle 64 of a wind turbine 60. As best illustrated in Fig. 7, the nacelle 64 is typically mounted, fixedly or rotatably, to a support structure 62 such as a post or a mast, the latter being typically fixedly secured to the ground.

[0044] While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.