AU2010249135B8

AU2010249135B8 - Wind turbine rotor designing method, wind turbine rotor design support device, wind turbine rotor design support program and wind turbine rotor

Info

Publication number: AU2010249135B8
Application number: AU2010249135A
Authority: AU
Inventors: Hideyasu Fujioka; Yoshihiko Hayashi; Yoshiyuki Hayashi; Takao Kuroiwa; Akihiro Nakamura
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2010-08-31
Filing date: 2010-08-31
Publication date: 2013-07-04
Anticipated expiration: 2030-08-31
Also published as: AU2010249135A1; AU2010249135B2; AU2010249135A8

Abstract

There is provided a designing method of a wind turbine rotor which includes a rotor head, a bearing provided on the rotor head and a wind turbine blade attached to the 5 bearing. The wind turbine rotor designing method includes: providing operation environment data indicative of an operation environment of a wind turbine generator including the wind turbine rotor and design data of the wind turbine blade; calculating a position of a center of 10 mass of the wind turbine blade in each position in a lengthwise direction of the wind turbine blade in the operation environment from the operation environment data and the design data; and calculating an evaluation value which is a value depending on an integral value obtained 15 by integrating a product of the calculated position of the center of mass of the blade and a mass per unit length at each position in a lengthwise direction of the wind turbine blade from a blade root portion of the wind turbine blade to a blade tip end of the same.

Description

DESCRIPTION WIND TURBINE ROTOR DESIGNING METHOD, WIND TURBINE ROTOR DESIGN SUPPORT DEVICE, WIND TURBINE ROTOR DESIGN SUPPORT PROGRAM AND WIND TURBINE ROTOR 5 Technical Field The present invention generally relates to a wind turbine rotor designing method, a wind turbine rotor design support apparatus and a wind turbine rotor, and in 10 particular to a designing technique for avoiding a contact of a wind turbine blade used in a wind turbine generator with a tower and further reducing the pitch moment. Background Art 15 One problem accompanied by extension of the diameter of the wind turbine rotor of an upwind type wind turbine generator, that is, large-scaling of the wind turbine blades is increase in the bending amount of the wind turbine blades due to the wind load. A wind turbine blade may 20 contact the tower when the bending amount of the wind turbine blade is increased, and it is therefore necessary that the wind turbine generator is designed so as to avoid contact of wind turbine blades with the tower in consideration of the bending amount of the wind turbine 25 blades. Three techniques are known for avoiding contact of the wind turbine blades with the tower. A first technique 2 is to previously incline the pitch axes of the wind turbine blades (axes about which the wind turbine blades rotate) toward the windward side (i.e., provision of the cone angle). A second technique is to previously bend the wind 5 turbine blades toward the windward side (i.e., pre-bend) A third technique is to make blade root attachment planes have an inclination angle with respect to the pitch axes so that the wind turbine blades are diagonally attached with respect to the pitch axes (i.e., root cut). In any 10 of these techniques, the tip ends of the wind turbine blades are kept away from the tower and the contact of the wind tower blades with the tower is effectively avoided. Such techniques are disclosed in, for example, U.S. Patent Publication No. 2009/0304513 A1, U.S. Patent 6,582,196 B1, 15 U.S. Patent Publication No. 2010/0104444 Al, and German Patent Application No. 10 2006 041 383 Al. The mere use of these techniques does not, however, dissolve a problem that the pitch moment required for rotating a wind turbine blade about the pitch axis is 20 increased when the wind turbine blade is large-sized and the imbalance of load exerting on the blade rotation bearing is increased. Rather, in some case, there is even a case that the imbalance of the load exerted on the blade rotation bearing is increased on the contrary. The 25 increase in the pitch moment necessitates increase in the driving ability of the pitch control mechanism which is mounted on the rotor head, and this is not preferable in 3 designing a wind turbine generator. If the pitch moment required for rotating the wind turbine blade about the pitch axis is reduced by the design of the wind turbine blades, however, such a problem would be avoided. 5 According to a study by the inventors, use of an optimum designing technique allows reducing the pitch moment required for rotating a wind turbine blade about the pitch axis. No reference is found in the known techniques mentioned above as to reduction of the pitch moment. 10 Citation List Patent Literature Patent literature 1: U.S. Patent Publication No. 2009/0304513 Al; Patent literature 2: U.S. Patent 6, 582, 196 B1; Patent literature 3: U.S. Patent Publication No. 2010/0104444 Al; and is Patent literature 4: German Patent Application No. 10 2006 041 383 Al. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the disadvantages of the prior art, or to provide a useful 20 alternative. Summary of the Invention The present invention at least in a preferred embodiment provides a designing technique for reducing the pitch moment required for rotating a wind turbine blade about 25 the pitch axis. In an aspect of the present invention, there is 4 provided a designing method for designing, by simulation, a wind turbine rotor including a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre-bend in an x-axis direction defined as being perpendicular to said z axis direction so that a plane defined by said x-axis direction and said z-axis direction is perpendicular to a rotation plane of said wind turbine rotor, said method comprising: providing operation environment data and design data, wherein said operation environment data are indicative of an operation environment of a wind turbine generator including said wind turbine rotor, and said design data are indicative of the structure of said wind turbine blade; calculating a position of a center of mass of said wind turbine blade at each position in said z-axis direction of said wind turbine blade in said operation environment from said operation environment data and said design data; calculating an evaluation value which is a value depending on an integral value obtained by integrating a product of said calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revising said design data based on said evaluation value so as to reduce said integral value, wherein said step of revising said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature. In one embodiment, the operation environment data preferably includes first data indicative of the rated wind speed of the wind turbine generator and second data indicative of the lowest temperature at which the wind turbine generator is allowed to be operated or the air density corresponding to the lowest temperature. The evaluation value F may be calculated using Equation (1) as below: 5 f =x(:)m(z)dz, ..(1) where, in Equation (1), the z-axis is defined as the direction along the center axis of the bearing, and the x-axis is defined as being perpendicular to the z-axis so 5 that a plane including the x-axis and z-axis is perpendicular to the rotation plane of the wind turbine rotor; x (z) is the position of the center of mass of the wind turbine blade in the x-axis direction in the operation environment; m(z) is the mass per unit length of the wind 10 turbine blade at the coordinate z on the x-axis; zo is the position of the blade root of the wind turbine blade on the z-axis; and zi is the position of the blade tip end on the z-axis. In one embodiment, x(z) is calculated using the 15 following equation: x(z) = Ax(z) - AXPRE(Z) - z sine, where Ax (z) is the displacement of the center of mass of the blade in the x-axis direction due to a wind load, and the pre-bend amount axPRE(Z) is the position at the 20 coordinate z of the center of mass of the wind turbine blade in the x-axis direction with no load, and the root cut inclination angle e is the angle between the extending direction of the wind turbine blade at said blade root portion and the center axis of said bearing. 25 In the wind turbine rotor designing method, it is preferable to revise the design data so as to further reduce 6 the integral value. In a case where the blade root portion of the wind turbine blade is in a cylindrical shape, the extending direction of the wind turbine blade at the blade root portion may be defined as a center line of the cylindrical shape. In another aspect of the present invention, there is provided a design support apparatus for designing, by simulation, a wind turbine rotor that includes a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z-axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre bend in an x-axis direction defined as being perpendicular to said z-axis direction so that a plane defined by said x-axis direction and said z-axis direction is perpendicular to a rotation plane of said wind turbine rotor, said apparatus comprising: a storage device for storing operation environment data and design data, wherein said operation environment data are indicative of an operation environment of a wind turbine generator including said wind turbine rotor, and said design data are indicative of the structure of said wind turbine blade; a processing unit, wherein said processing unit is programmed to: calculate a position of a center of mass of said wind blade at each position in said z-axis direction of said wind turbine blade in said operation environment from said operation environment data and said design data; calculate an evaluation value which depends on an integral value obtained by integrating a product of the calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revise said design data based on said evaluation value so as to reduce said integral value, wherein the revision of said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which 7 said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature. In still another aspect of the present invention, there is provided a recording medium recoding a design support program for designing, by simulation, a wind turbine rotor which includes a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre-bend in an x-axis direction defined as being perpendicular to said z axis direction so that a plane defined by said x-axis direction and said z-axis direction is perpendicular to a rotation plane of said wind turbine rotor, said program causing a computer to perform the following steps of: calculating a position of a center of mass of said wind turbine blade at each position in said z-axis direction of said wind turbine blade in an operation environment, based on operation environment data indicative of the operation environment of a wind turbine generator including said wind turbine rotor and design data indicative of the structure of said wind turbine blade, wherein the operation environment data and the design data are prepared in a storage device; and calculating an evaluation value which depends on an integral value obtained by integrating a product of said calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revising said design data based on said evaluation value so as to reduce said integral value, wherein said step of revising said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature.

7a In an embodiment of the present invention, a wind turbine rotor includes a rotor head, a bearing provided on the rotor head and a wind turbine blade attached to the bearing. For a case where a first direction is defined as the direction along the center axis of the bearing and a second direction is defined as being perpendicular to the first direction so that a plane defined by the first and second directions is perpendicular to a rotation plane of the wind turbine rotor, the wind 8 turbine blade is so formed as to have such a shape that, for a tangent line at an agreement position at which a center of mass of the wind turbine blade meets the center axis of the bearing other than the blade root of the wind turbine blade to a curve of a change of the displacement in the second direction of the center of mass due to a wind load with respect 5 to the distance from the blade root in the first direction in a case where the temperature is the lowest temperature at which a wind turbine generator provided with the wind turbine rotor is allowed to be operated and a wind blows at the rated wind speed, a portion of the curve away from the agreement position is located between the tangent line and the center axis of the bearing. 10 The present invention at least in a preferred embodiment provides a designing technique for reducing the pitch moment required for rotating the wind turbine blade about the pitch axis. IS Brief Description of Drawings Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings wherein: Fig. 1 is a side view showing the configuration of a wind turbine generator in one embodiment; 20 Fig. 2 is a perspective view showing an example of a connection structure between a rotor head and a wind turbine blade in one embodiment; Fig. 3A is a plan view showing an example of the shape of the blade surface of the wind turbine blade; Fig. 3B is a front view showing the structure of the wind turbine blade viewed 25 from the blade chord direction; 9 Fig. 4 is a side view showing the relationship between the central axis of a bearing of a wind turbine rotor and a center line of the blade root portion of the wind turbine blade; 5 Fig. 5 is a diagram showing the positional relationship between the blade root portion of the wind turbine blade and the blade section in the A-A section in a case in which "root cut" is not adopted; Fig. 6 is a graph showing a change of a position of 10 a center of mass of a blade in the windward direction (x-axis direction) with respect to the position in the pitch axis direction (z-axis direction) fromtheblade root portion in a case when "pre-bend" is adopted without adopting "root cut"; 15 Fig. 7 is a diagram showing positional relationships between the blade root portion of the wind turbine blade and the blade section in the A-A and B-B sections in a case when "root cut" is adopted; Fig. 8 is a graph showing a change of the position 20 of the center of mass of a blade in the windward direction (x-axis direction) with respect to the position in the pitch axis direction (z-axis direction) from the blade root in a case when "pre-bend" and "root cut" are adopted; Fig. 9 is a graph showing a change of the position 25 of the center of mass of the blade in the windward direction (x-axis direction) with respect to the position in the pitch axis direction (z-axis direction) from the blade 10 root; and Fig. 10 is a block diagram showing the configuration of a wind turbine rotor design support apparatus in one embodiment. 5 Embodiments of Invention Fig. 1 is a side view showing the configuration of an upwind type wind turbine generator in one embodiment. The wind turbine generator 1 is provided with a tower 2 10 stood on a foundation 7, a nacelle 3 installed on a top end of the tower 2, and a wind turbine rotor 4. The wind turbine rotor 4 includes a rotor head 5 rotatably attached to the nacelle 3, and three wind turbine blades 6 attached to the rotor head 5. The rotation axis of the wind turbine 15 rotor 4 (wind turbine rotation axis 4a) is directed in the horizontal direction or slightly upward than the horizontal direction in the windward direction. When the wind turbine rotor 4 is rotated by wind power, the wind turbine generator 1 generates electric power and supplies 20 the power to the utility grid connected with the wind turbine generator 1. Fig. 2 is a perspective view showing a connection structure of the rotor head 5 and the wind turbine blades 6. Three bearings 8 (only one shown) are attached to the 25 rotor head 5. The bearings 8 rotatably support the wind turbine blades 6, and the center axes of the bearings 8 corresponds to the rotation axes of the wind turbine blades 11 6, that is, the pitch axes. The pitch angle of the wind turbine blades 6 is variable by the bearing 8. Figs. 3A and 3B are diagrams showing an example of the structure of the wind turbine blades 6. Fig. 3A shows 5 the configuration of the blade surface of a wind turbine blade 6, and Fig. 3B shows the structure of the wind turbine blade 6 viewed from the blade chord direction. In this embodiment, while the blade root portion 6a of the wind turbine blade 6 is formed in a cylindrical shape, a blade 10 shape is formed in the middle portion and tip portion of the wind turbine blade 6. The blade-shaped portion and the blade root portion 6a are smoothly joined. In addition, in this embodiment, out of the blade surfaces of the wind turbine blade 6, the blade surface 6c on the windward side 15 is formed to be concave and the blade surface 6d on the leeward side is formed to be convex, so that the tip end portion of the wind turbine blade 6 is curved in the windward direction. This aims to avoid contact between the wind turbine blade 6 and the tower 2. In Figs. 3A and 20 3B, the center line (and the extension line) of the wind turbine blade 6 in the blade root portion 6a is denoted by numeral 10. As shown in Fig. 3B, the blade tip end 6b of the wind turbine blade 6 is offset in the windward direction with respect to the center line 10. Also, in 25 Figs. 3A and 3B, the blade root of the wind turbine blade 6 is denoted by numeral 6e. Fig. 4 is a side view showing the relationship between 12 the center axis (i.e., the pitch axis) of a bearing 8 and the center line 10 of the blade root portion 6a. The pitch axis is denoted by numeral 9 in Fig. 4. The terms used in the following description are defined as below referring 5 to Fig. 4: (1) Wind Turbine Rotation Plane The wind turbine rotation plane 12 is a flat plane perpendicular to the wind turbine rotation axis 4a. 10 (2) Cone angle The cone angle a is an angle defined between the pitch axis 9 and the wind turbine rotation plane 12. More strictly, the cone angle a is an angle defined between a 15 straight line and the pitch axis 9, wherein the straight line is defined by a plane which includes the pitch axis 9 and is perpendicular to the wind turbine rotation plane 12 and by the wind turbine rotation plane 12. 20 (3) Root Cut Inclination Angle The root cut inclination angle e is an angle defined between the extending direction of the wind turbine 6 in the blade root portion 6a and the pitch axis 9. Here, in this embodiment, since the blade root portion 6a is formed 25 in a cylindrical shape, the root cut inclination angle e is defined as an angle formed between the center line of the cylindrical shape of the blade root portion 6a and the 13 pitch axis 9. In this embodiment, a non-zero root cut inclination angle E is given by cutting off the cylindrical blade root portion 6a at a bevel. Herein, the z-axis direction is defined as the 5 direction along the pitch axis 9. It should be noted that z = 0 at the blade root 6e of the wind turbine blade 6. In addition, the x-axis direction is defined as a direction perpendicular to the z-axis direction in the windward direction. Here, the x-axis direction is determined so 10 that a plane defined by the x-axis and the z-axis is perpendicular to the wind turbine rotation plane 12. As described above, there are known three techniques for avoiding that a wind turbine blade 6 contacts the tower 2: 15 A first technique is to incline the pitch axis of the wind turbine 6 (the rotation center axis of the wind turbine 6) toward the windward side. This means that the cone angle a mentioned above is set non-zero. This technique is referred to as "non-zero cone angle", hereinafter. 20 A second technique is to bend the tip portion of the wind turbine 6 toward the windward side in the manufacture. This technique is referred to as "pre-bend", hereinafter. A third technique is to cut the blade root portion 6a of the wind turbine blade 6 at a bevel so as to diagonally 25 attach the wind turbine blade 6 with respect to the pitch axis 9. This means that the root cut inclination angle e mentioned above is set non-zero. This technique is 14 referred to as "root cut", hereinafter. These techniques are all effective for avoiding a contact of the wind turbine blade 6 with the tower 2. Although the easiest and most widely used technique is 5 "non-zero cone angle", only the use of the "non-zero cone angle" cannot avoid the contact of the wind turbine blade 6 with the tower 2 for a large-size wind turbine blade 6. According to study by the inventor, it is therefore preferable to combine another technique with the "non-zero 10 cone angle". Herein, one idea of the inventor is that the "non-zero cone angle", "pre-bend" and "root cut" have respectively different influences on the pitch moment Mzb (the moment required for rotating the wind turbine blade 6 about the 15 pitch axis 9) and that the pitch moment Mzb can be reduced by appropriately combining these techniques. The following discusses the influences on the pitch moment Mzb caused by the "non-zero cone angle", "pre-bend" and "root cut". 20 When only the "non-zero cone angle" is used, the wind turbine blade 6 is positioned on the pitch axis 9 at no load. Accordingly, the use of only the "non-zero cone angle" results in that the tip portion of the wind turbine blade 6 is moved away from the pitch axis 9 to thereby 25 increase the pitch moment Mzb, when the wind turbine blade 6 is bent by the wind load. On the other hand, the use of the "pre-bend" reduces 15 the pitch moment Mzb, since the tip portion of the wind turbine blade 6 can be brought close to the pitch axis 9 when the wind turbine blade 6 is bent by the wind load. Here, according to the study by the inventors, it is 5 the "root cut" that is most effective for reducing the pitch moment Mzb. In the following, a description is given of the effect of reduction of the pitch moment Mzb by the "root cut", referring to Figs. 5 to 9. Fig. 5 shows the relationship between the blade root 10 portion 6a of the wind turbine blade 6 and a blade section llA in a case when the "root cut" is not adopted. Herein, the left figure of Fig. 5 shows the positional relationship between the blade root portion 6a of the wind turbine blade 6 and the blade section llA in the case where the wind 15 turbine blade 6 is located at an azimuth angle of 2700 and the right figure of Fig. 5 shows the positional relationship between the blade root portion 6a of the wind turbine blade 6 and the blade section llA in the case where the wind turbine blade 6 is located at an azimuth angle 20 of 900. It should be noted here that the "azimuth angle" means the position of the wind turbine blade 6 in the circumferential direction of the wind turbine rotation axis 4a and the azimuth angle is defined to be 0* in the case where the wind turbine blade 6 is located in the 25 vertical upward direction or in the direction closest thereto. The blade section 11A is within the A-A section in Figs. 3A and 3B, that is, the blade section of the wind 16 turbine blade 6 at a position slightly closer to the blade tip end 6b from the midpoint of the wind turbine blade 6. As shown in Fig. 5, when a wind load is applied, the wind turbine blade 6 is bent and the blade section llA is 5 moved away from the pitch axis 9. The bearing 8 for rotating the wind turbine blade 6 is applied with an asymmetric load by the self weight and the aerodynamic force in proportion to the bending amount of the wind turbine blade 6 so that the pitch moment Mzb is increased. 10 Fig. 6 is a graph showing a change in the position x(z) of the center of mass of the blade in the windward direction (x-axis direction) with respect to the coordinate z in the pitch axis direction (z-axis direction) from the blade root 6e in a case when the "pre-bend" is used without using the 15 "root cut". It should be noted here that the position x (z) of the center of mass of the blade in the coordinate z in the pitch axis direction means the position of the center of mass the blade calculated for the blade section perpendicular to the pitch axis 9 passing through the 20 coordinate z. With no load, the center of bass of the blade is located in proximity to the pitch axis 9 as a whole, although the bent tip portion of the wind turbine blade 6 is located slightly away from the pitch axis 9 in the windward direction. When a wind load corresponding to the 25 rated wind speed is applied, the wind turbine blade 6 is bent toward the leeward side, and the center of mass of the blade is moved farther away from the pitch axis 9 as 17 the position is approached nearer to the blade tip end 6b of the wind turbine blade 6. Thus, the asymmetricity of the load applied to the bearing 8 which rotates the wind turbine blade 6 is increased so as to increase the pitch moment Mzb required for rotating 5 the wind turbine blade 6 about the pitch axis 9. On the other hand, Fig. 7 shows positional relationships between the blade root portion 6a of the wind turbine blade 6 and the blade sections 1 IA and 1 B in a case when the "root cut" is used. The left figure of Fig. 7 shows the positional relationship between 10 the blade root portion 6a of the wind turbine blade 6 and the blade sections 1 IA and 1 l B in the case where the wind turbine blade 6 is located at an azimuth angle of 2700 and the right figure of Fig. 7 shows the positional relationship between the blade root portion 6a of the wind turbine blade 6 and the blade sections 1 IA and 1 B in the case where the wind turbine blade 6 is located at an azimuth angle of 90*. It should be noted here that the is blade section 1 B is within the B-B section in Figs. 3A and 3B, that is, the blade section of the wind turbine blade 6 at a position slightly closer to the blade root 6e from the midpoint of the wind turbine blade 6. That is, the blade section 1 A is located relatively away from the blade tip end 6b of the wind turbine blade 6 and the blade section 1 B is located relatively close to the blade root portion 6a of the wind turbine blade 6.

18 One feature of the wind turbine blade 6 adopting the "root cut" is that, in a case where the wind turbine blade 6 is bent by a wind load, the portion close to the blade root portion 6a of the wind turbine blade 6 is located on the windward side with respect to the pitch axis 9 while the portion close to the blade tip end 6b is located on the leeward side 5 with respect to the pitch axis 9. This is shown by the fact that the blade sections II A and 11 B are located in opposite sides across the pitch axis 9 in any of the cases of an azimuth angle 2700 or 90" in Fig. 7. Also, as shown in Fig. 8, the center of mass of the blade is located on the windward side with respect to the pitch axis 9 in a region B, and the center of mass of the blade is located on the leeward side with respect to the pitch axis 9 in a io region A. Thus, the pitch moments Mzb due to the self weight of the portion close to the blade root portion 6a and the self weight of the portion close to the blade tip end 6b of the wind turbine blade 6 are cancelled to each other so that the pitch moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9 is reduced. is When the wind turbine rotor 4 is so designed as to reduce the pitch moment Mzb, it is necessary to pay attention to the fact that the pitch moment Mzb depends on the operation environment of the wind turbine generator 1. The pitch moment Mzb is maximized, when the temperature is the lowest temperature at which the wind turbine 19 generator 1 is allowed to be operated and the wind turbine generator 1 is operated in the operation environment in which the wind blows at the rated wind speed. That is, the temperature is related to the air density, which 5 becomes maximum when the temperature is the lowest temperature. When the actual wind speed is smaller than the rated wind speed, the wind turbine generator 1 is so controlled as to be placed in the fine state where the pitch angle of the wind turbine blades 6 is minimum (i.e., the 10 state in which the received wind power energy is maximum) or to be a pitch angle approximate thereto, and when the effective wind speed exceeds the rated wind speed, the pitch angle is increased as the wind speed is increased so as to be in a state close to the feather state (i.e., 15 the state in which the received wind power energy is minimum) . When such operation is implemented, the pitch moment Mzb is maximum when the actual wind speed is the rated wind speed. As a result, since the pitch moment Mzb becomes maximum when the temperature is the lowest 20 temperature at which the wind turbine generator 1 is allowed to be operated and the wind blows at the rated wind speed, it is preferable to design the wind turbine rotor 4 so that the pitch moment Mzb is reduced in this case. In a preferred example of a design of the wind turbine 25 rotor 4, a curve of the change in the position x(z) of the center of mass of the wind turbine blade 6 in the windward direction with respect to the coordinate z in the pitch 20 axis direction (z-axis direction) from the blade root 6e satisfies the following requirement, under conditions in which the pitch moment Mzb becomes maximum (i.e., when the temperature is the lowest temperature at which the wind 5 turbine generator 1 is allowed to be operated and the wind blows at the rated wind speed) (see Fig. 9): Requirement: For a tangent line L drawn at a position Q at which 10 the position x(z) of the center of mass of the blade meets the pitch axis 9 other than the blade root 6e, the portion of the curve away from the position Q is located between the tangent line L and the pitch axis 9 (the z-axis). The design of the wind turbine blade 6 satisfying such 15 a requirement, the balance is improved between the portion located on the windward side with respect to than the pitch axis 9 and the portion located on the leeward side with respect to than the pitch axis 9 when the wind turbine blade 6 is bent, and thereby the pitch moment Mzb is reduced. 20 It should be noted that it is important to adopt the "root cut" in terms of the reduction of only the pitch moment Mzb and it is not always necessary to adopt the "non-zero cone angle" and "pre-bend". On the other hand, it is effective to adopt the "non-zero cone angle" and/or 25 "pre-bend" in view of avoiding the contact between the wind turbine blade 6 and the tower 2. Accordingly, it is appropriate to adopt the "root cut" in addition to the 21 "non-zero cone angle" and/or "pre-bend", as a whole of the actual wind turbine rotor 4. Here, when the "root cut" is adopted, it is important to optimize the root cut inclination angle e. If the root 5 cut inclination angle e is too large, the balance between the portion located on the windward side with respect to the pitch axis 9 and the portion located on the leeward side is lost when the wind turbine blade 6 is bent due to a wind load, which rather results in increase of the pitch 10 moment Mzb. Also, when the "pre-bend" is adopted, the balance between the portion located on the windward side with respect to the pitch axis 9 and the portion located on the leeward side in a case where the wind turbine blade 6 is bent depends on the degree of the "pre-bend". 15 Accordingly, in order to determine the root cut inclination angle e to be optimum, it is necessary to take into consideration of the pre-bend amounts at respective positions of the wind turbine blade 6 in the pitch axis direction (i.e., the positions of the center of mass of 20 the blade in the x-axis direction at respective positions of the wind turbine blade 6 in the pitch axis direction for no load). The following discusses a technique for optimally designing the root cut inclination angle e. As described above, in order to reduce the pitch 25 moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9, the balance between the portion of the wind turbine blade 6 located on the windward side 22 with respect to the pitch axis 9 and the portion located on the leeward side is important. One technique for evaluating such a balance is to calculate an evaluation value based on an integral value f obtained by integrating 5 a product of the position x(z) of the center of mass of the wind turbine blade 6 with the wind load applied and the mass m(z) per unit length at each position of the wind turbine blade 6 in the z-axis direction from the blade root 6e to the blade tip end 6b of the wind turbine blade 6. 10 The integral value f is expressed by the following Equation (1): f= x(:)n(:)d:, --(1) where z is the position in the z-axis direction (in the direction along the pitch axis 9), zo is the position of 15 the blade root 6e of the wind turbine blade 6 on the z-axis, and zi is a position of the blade tip end 6b of the wind turbine blade 6 on the z-axis. In one embodiment, the integral value f per se may be used as the evaluation value. In this case, the 20 evaluation value F is expressed by the following Equation (2): F = J'x(:)m(:)d:. ---(2) The evaluation value F is not necessarily the integral value f per se; the evaluation value F may be a value 23 obtained by applying some calculation to the integral value f, or may be a value calculated in consideration of a parameter other than the integral value f. In one embodiment, the position x(z) of the center 5 of mass of the wind turbine blade 6.with the wind load applied may be calculated by the following Equation (3) x(z) = Ax(z) - AXPRE (z) - z sinG, (3) where Ax (z) is the displacement of the center of mass of the blade in the x-axis direction by the wind load, AXPRE(z) 10 is the pre-bend amount of the wind turbine blade 6 at the coordinate z, that is, the position of the center of mass of the wind turbine blade 6 in the x-axis direction at the coordinate z, and 0 is the root cut inclination angle, that is, the angle defined between the extending direction of 15 the wind turbine blade 6 at the blade root portion 6a and the center axis of the bearing 8. In this case, Equation (4) is obtained as below from Equations (2) and (3): F= (Ax(:) - Ax,() -sin O)n(:)d-. -.- (4) 20 In one embodiment, the evaluation value F may be obtained using Equation (4). Also, when z is 0 at the position of blade root 6e of the wind turbine blade 6 and z is R at the position of the blade tip end 6b (in the case where the blade length of the wind turbine blade 6 is R) , Equation 25 (5) is obtained as below: 24 F = (Ax(:)- Ax 1 ,R(:)- sinO)m(:)d:. -.. (5) In one embodiment, the evaluation value F may be obtained using Equation (5). Herein, the position x(z) of the center of mass of 5 the blade in a case when a wind load is applied (or the displacement Ax (z) of the center of mass of the blade caused by the wind load) depends on the operation environment in which the wind turbine generator 1 is operated. As the operation environment, there are recited the air density, 10 temperature and wind speed. It should be noted here that the air density and the temperature are fundamentally equivalent parameters, since the air density depends on the temperature. In one embodiment, the evaluation value F is calculated as a function that depends on the 15 temperature T and the wind speed v. The balance between the pitch moments Mzb of the portion of the wind turbine blade 6 located on the windward side with respect to the pitch axis 9 and the portion located on the leeward side with respect to the pitch axis 9 can be evaluated for a 20 desired temperature T and wind speed v, by calculating the position x(z) (or the displacement Zax (z) ) for the desired temperature T and wind speed v, and further calculating the evaluation value F from the calculated position x(z) (or the displacement Ax (z)). Instead, the evaluation 25 value F may be calculated as a function that depends on 25 the air density p and the wind speed v. In this case, the balance between the pitch moments Mzb of the portion of the wind turbine blade 6 located on the windward side with respect to the pitch axis 9 and the portion located on the 5 leeward side can be evaluated for the air density p and the wind speed v. Herein, as described above, the pitch moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9 becomes maximum in the case where the 10 temperature T is the lowest temperature TLOW at which the wind turbine generator 1 is allowed to be operated (or the air density p is the maximum air density PMAx) and the wind speed is the rated wind speed VRATED. Accordingly, the position x(z) of the center of mass of the blade (or the 15 displacement Ax(z)) is calculated for the lowest temperature TLOW (or the maximum air density PMAx) and the rated wind speed VRATED so that the evaluation value F calculated using the calculated position x (z) (or the displacement Ax(z)) is the most suitable value for 20 evaluating the balance between the pitch moments Mzb by the self weighs of the portions of the A and B regions of the wind turbine blade 6. The pitch moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9 can be further reduced by determining the root cut 25 inclination angle E and the shape of the wind turbine blade 6 (in particular, the pre-bend amount AXPRE(Z)) so as to minimize the evaluation value F calculated with respect 26 to the lowest temperature TLow (or the maximum air density PMAx) and the rated wind speed VRATED The designing technique described above may be implemented using a wind turbine rotor design support 5 apparatus 20 shown in Fig. 10. The wind turbine rotor design support apparatus 20 is configured as a computer that includes an input device 21, an output device 22, a CPU 23, a memory 24 and an external storage device 25. The input device 21 and the output device 22 configure a 10 man-machine interface of the wind turbine rotor design support apparatus 20. The input device 21 is provided with a key board and a mouse, for example. The output device 22 is provided with a monitor and a printer for example. A wind turbine rotor design support program 26 is installed 15 onto the external storage device 25. The wind turbine rotor design support program 26 is a computer program for aiding the above-described designing technique. The CPU 23 executes the wind turbine rotor design support program 26 using the memory 24. The wind turbine rotor design 20 support program 26 includes: a simulator for calculating the position x (z) of the center of mass of the wind turbine blade 6 in the windward direction (x-axis direction) with a wind load applied for the desired operation environment (e.g., temperature T, air density p and wind speed v) or 25 the displacement Ax(z) due to the wind load; a code module for calculating the evaluation value F; and a structure design tool for designing the structure of the wind turbine 27 blade 6. A description is given below of a preferred example of the procedure of designing a wind turbine blade 6 using the wind turbine rotor design support apparatus 20 s shown in Fig. 10. It should be noted that, in the following, a description is given of a case when the evaluation value F is calculated using Equation (5) from the lowest temperature TLow and the rated wind speed vRATED. It would be, however, obvious for the person skilled in the art that the evaluation value may be calculated in a similar procedure by using Equations (2) and (4) and that the maximum air density pMAX may be used instead 10 of the lowest temperature TLow. Design data of the wind turbine blade 6 is previously prepared in the external storage device 25. The design data include data indicative of the structure of the wind turbine blade 6 (the pre-bend amount AxPRE(z) at the coordinate z of the wind turbine Is blade 6, the blade length R of the wind turbine blade 6 and the mass per unit length m(z) of the wind turbine blade 6 at the coordinate z and so on) and include data indicative of other mechanical characteristics. The design data may be produced using the structure design tool of the wind turbine rotor design support program 26 or externally given using the input device 21. 20 Moreover, the lowest temperature TLow at which the wind turbine generator 1 is allowed to be operated and the 28 rated wind speed VRATED are inputted via the input device 22 and stored onto the external storage device 25. The wind turbine rotor design support program 26 calculates the displacement Ax(z) of the center of mass 5 of the blade in the windward direction (x-axis direction) due to the wind load using the simulator for the given lowest temperature TLOw and the rated wind speed VRATED. The design data of the wind turbine blade 6 are used in the calculation of.the displacement Ax(z). The calculated 10 displacement Ax(z) of the center of mass of the blade in the windward direction (x-axis direction) due to the wind load is stored in the external storage device 25. Further, the wind turbine rotor design support program26 calculates the evaluation value Fusing Equation 15 (5) mentioned above. This evaluation value F indicates a degree of the balance between the pitch moments Mzb of the portion of the wind turbine blade 6 located on the windward side with respect to the pitch axis 9 and the portion located on the leeward side with respect to the 20 pitch axis 9. The pitch moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9 is reduced as the evaluation value F is reduced. A user seeing the evaluation value F may revise the design data of the wind turbine blade 6 using the structure 25 design tool of the wind turbine rotor design support program 26, if necessary. By revising the pre-bend amount AxPRE (z) and/or the root cut inclination angle e in 29 accordance with the necessity, the evaluation value F can be reduced, that is, the pitch moment Mzb required for rotating the wind turbine blade 6 about the pitch axis 9 can be reduced. It should be noted here that, reduction 5 of the evaluation value F is equivalent to reduction of the integral value f of Equation (1) in the calculation of the evaluation value F using Equation (5) . The structure design tool of the wind turbine rotor design support program 26 may be used in revising the design data. 10 The designing procedure as described above allows designing the wind turbine blade 6 with a reduced pitch moment Mzb required for rotation about the pitch axis 9.

Claims

1. A designing method for designing, by simulation, a wind turbine rotor including a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre-bend in an x-axis direction defined as being perpendicular to said z axis direction so that a plane defined by said x-axis direction and said z-axis direction is perpendicular to a rotation plane of said wind turbine rotor, said method comprising: providing operation environment data and design data, wherein said operation environment data are indicative of an operation environment of a wind turbine generator including said wind turbine rotor, and said design data are indicative of the structure of said wind turbine blade; calculating a position of a center of mass of said wind turbine blade at each position in said z-axis direction of said wind turbine blade in said operation environment from said operation environment data and said design data; calculating an evaluation value which is a value depending on an integral value obtained by integrating a product of said calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revising said design data based on said evaluation value so as to reduce said integral value, wherein said step of revising said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature.

2. The designing method according to claim 1, wherein said evaluation value is an evaluation value F calculated using the following Equation (1): F = x(c)mf(C)d:, -() 31 wherein x(z) is a position of the center of mass of said wind turbine blade in said x-axis direction in said the operation environment for a coordinate z in said z-axis direction, wherein m (z) is a mass per unit length of said wind turbine blade at the coordinate z in said z-axis direction, wherein zo is a position of said blade root in said z-axis direction, and wherein zi is a position of said blade tip end in said z-axis direction.

3. The designing method according to claim 2, wherein x(z) is calculated using the following Equation (2): x(z) = Ax(z) - AxPRE(Z) - z sin 0, ... (2) wherein Ax(z) is a displacement of said center of mass of the blade in said x-axis direction due to a wind load, wherein AxPRE (z) is the position of said center of mass of said wind turbine blade in said x-axis direction with no load for the coordinate z, and wherein said root cut inclination angle 0 is an angle between an extending direction of said wind turbine blade in said blade root portion and the center axis of said bearing.

4. The designing method according to claim 3, wherein said blade root portion of said wind turbine blade is in a cylindrical shape, and wherein the extending direction of said wind turbine blade at said blade root portion is defined as a center line of said cylindrical shape.

5. A design support apparatus for designing, by simulation, a wind turbine rotor that includes a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z-axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre-bend in an x-axis direction defined as being perpendicular to said z-axis direction so that a plane defined by said x-axis direction and said z axis direction is perpendicular to a rotation plane of said wind turbine rotor, said apparatus comprising: a storage device for storing operation environment data and design data, wherein said operation environment data are indicative of an operation environment of a wind turbine generator including said wind turbine rotor, and said design data are indicative of the structure of 32 said wind turbine blade; a processing unit, wherein said processing unit is programmed to: calculate a position of a center of mass of said wind blade at each position in said z-axis direction of said wind turbine blade in said operation environment from said operation environment data and said design data; calculate an evaluation value which depends on an integral value obtained by integrating a product of the calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revise said design data based on said evaluation value so as to reduce said integral value, wherein the revision of said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature.

6. A recording medium recoding a design support program for designing, by simulation, a wind turbine rotor which includes a rotor head, a bearing provided on said rotor head and a wind turbine blade attached to said bearing, said wind turbine blade having a root cut inclination angle 0 that is non-zero with respect to a z-axis direction defined along a center axis of said bearing; and having at least one of a cone angle a that is non-zero and a pre-bend in an x-axis direction defined as being perpendicular to said z-axis direction so that a plane defined by said x-axis direction and said z-axis direction is perpendicular to a rotation plane of said wind turbine rotor, said program causing a computer to perform the following steps of: calculating a position of a center of mass of said wind turbine blade at each position in said z-axis direction of said wind turbine blade in an operation environment, based on operation environment data indicative of the operation environment of a wind turbine generator including said wind turbine rotor and design data indicative of the structure of said wind turbine blade, wherein the operation environment data and the design data are prepared in a storage device; and calculating an evaluation value which depends on an integral value obtained by integrating 33 a product of said calculated position of said center of mass of the blade and a mass per unit length at each position in said z-axis direction of said wind turbine blade from a blade root of said wind turbine blade to a blade tip end of the same; and revising said design data based on said evaluation value so as to reduce said integral value, wherein said step of revising said design data includes determining said root cut inclination angle 0 and a position of said center of mass of said wind turbine blade in said x-axis direction with no load for each position of said wind turbine blade in said z-axis direction, so as to minimize said integral value, and wherein said operation environment data include first data indicative of a rated wind speed of said wind turbine generator and second data indicative of a lowest temperature at which said wind turbine generator is allowed to be operated or an air density corresponding to said lowest temperature.

7. The designing method according to claim 1, wherein the wind turbine blade is designed such that, said wind turbine blade is formed to have such a shape that, for a tangent line at an agreement position at which a center of mass of said wind turbine blade meets the center axis of said bearing other than said blade root of said wind turbine blade to a curve of a change of a displacement in said x-axis direction of said center of mass due to a wind load with respect to a distance from said blade root in said z-axis direction in a case where a temperature is said lowest temperature a wind blows said rated wind speed, a portion of said curve away from said agreement position is located between said tangent line and the center axis of said bearing.

8. A designing method for designing a wind turbine rotor, the method substantially as hereinbefore described with reference to the accompanying drawings.

9. A design support apparatus for designing a wind turbine rotor, the apparatus substantially as hereinbefore described with reference to the accompanying drawings.

10. A recording medium recording a design support program for designing a wind turbine rotor, the recording medium substantially as hereinbefore described with reference to the accompanying drawings. Mitsubishi Heavy Industries, Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON