Source: https://patents.google.com/patent/WO2010145902A1/en
Timestamp: 2018-04-23 03:37:10
Document Index: 114109867

Matched Legal Cases: ['art 34', 'art 136', 'art 141', 'art 141', 'art 141', 'art 236', 'art 241', 'art 243', 'art 241', 'art 243', 'arts 241', 'art 345', 'art 341', 'art 343', 'art 345', 'art 44', 'art 42', 'art 44', 'art 44', 'art 436', 'art 441', 'art 443', 'art 441', 'art 443', 'arts 441', 'arts 441', 'art 441', 'art 436', 'art 443', 'art 441', 'art 441']

WO2010145902A1 - Wind turbine blade with base part having inherent non-ideal twist - Google Patents
WO2010145902A1
WO2010145902A1 PCT/EP2010/056793 EP2010056793W WO2010145902A1 WO 2010145902 A1 WO2010145902 A1 WO 2010145902A1 EP 2010056793 W EP2010056793 W EP 2010056793W WO 2010145902 A1 WO2010145902 A1 WO 2010145902A1
PCT/EP2010/056793
A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft is described. The rotor comprises a hub, from which the blade extends substantially in a radial direction when mounted to the hub. The blade comprises a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, wherein the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge. The first base part has an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at a design point deviates from a target axial induction factor. The first longitudinal segment is provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the design point.
Title: Wind Turbine Blade with Base Part having inherent non-ideal twist
In other words, the invention provides a blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade having a predetermined target axial induction factor at a rotor design point, the blade compris- ing: a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region. The airfoil region may be divided into a number of base sections, a first one of said base sections extending along at least 20% of a longitudinal extent of the airfoil region, the first base section having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the first base section being formed with an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at the rotor design point deviates from a target axial induction factor, and the first base section is provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the rotor design point.
Further, a blade segment with an inherent non-optimum twist has a number of advan- tages with respect to manufacturing of the base part, since the shape of the base part can be kept much simpler than the shapes of conventional, modern wind turbine blades with a length of more than 40 meters. For instance double curvatured blade profiles may be avoided. This also makes the production of mould parts for manufacture of the blades simpler. All in all, the time for initial start-up for developing the design of a new blade type to the product launch of the new blade type may be lowered significantly, and the overall production costs may also be lowered.
However, putting such a constraint on the design parameters of the blade segment means that the blade segment deviates from the optimum design with respect to aero- dynamics, in which the ideal twist has a non-linear dependency on the radial position of the blade section. Thus, such a blade segment will inherently be non-ideal with respect to aerodynamics and in particular in relation to the axial induction factor. This deviation is compensated for by using flow altering devices in order to adjust the design lift and inflow properties to the appropriate near-optimum axial induction as a function of the blade radius. However, the target axial induction factor may deviate from the aerodynamic optimum axial induction of 1/3 due to structure and loading considerations.
The adjustment of the loading to another blade radius implies the need for use of flow altering devices. Thus, the flow altering devices are used to adjust the blade to the ro- tor design point so that it has a near-optimum inflow condition and lift coefficient. All in all, it is seen that the inventive concept behind the idea is a departure from the traditional process of designing modern wind turbine blades, where the outer shape and the aerodynamic performance of the blade are designed initially, and first afterwards it is determined how to plan the manufacturing of the blades in accordance with the design specification. The invention provides a new design process, in which the production is optimised in relation to effective methods of manufacturing a base part of a wind turbine blade, and where the base part of the blade is retrofitted with flow guiding devices in order to obtain the proper aerodynamic specifications. Thus, the base part of the blade may deviate substantially from the optimum aerodynamic design.
According to a first embodiment, the induction factor of the first base part without flow altering means deviates from the target axial induction factor along substantially the en- tire longitudinal extent of the first longitudinal segment.
According to another advantageous embodiment, the first longitudinal segment in the radial direction is divided into: a plurality of radial sections, each radial section having an individual average operating angle of attack for the design point and having a sec- tional airfoil shape, which without the first flow altering devices has a sectional optimum angle of attack, wherein the first flow altering devices are adapted to shift the optimum angle of attack of the sectional airfoil shape towards the average operating angle of attack for the radial section.
The first derivative of the twist is reduced with increasing distance from the hub. There- fore, the twist of the outer part of the blade, i.e. near the tip, is smaller than the twist of the inner part of the blade. Consequently, not all blades need to be provided with flow altering devices near the tip end. However, preferably at least the inner 40%, 50%, 60%, 70%, or 75% of the airfoil area is provided with radial blade section having flow altering devices. The inflow in the tip region may be compensated for by altering the blade pitch angle and/or the rotational speed of the rotor.
Advantageously, the root mean square difference over the longitudinal extent of the first longitudinal section between the average inflow angle and the optimum inflow of attack at the design point is more than 1 degree, or more than 2 degrees, or more than 2.5 degrees for the first longitudinal segment without flow altering devices. Thus, the root mean square difference is calculated as an absolute spatial deviation in the longitudinal direction of the blade. This deviation is further observed over a given time inter- val, e.g. one full cycle for a wind turbine rotor. Advantageously, the root mean square difference over the longitudinal extent of the first longitudinal section between the average inflow angle and the optimum inflow angle at the design point is less than 1 degree, or less than 0.5 degrees for the first longitudinal segment with the flow altering means.
According to yet another embodiment, the first base part without flow altering devices at the design point further deviates from a target loading, and wherein the first flow altering devices are further arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target loading at the design point. The target loading is in this regard considered to be the resultant air force or more accurately the resultant normal force to the rotor plane influencing the particular blade section. The target loading may be seen as an average over the entire longitudinal ex- tent of the first longitudinal segment, or it may be seen as an individual target for a plurality of smaller radial segments within the first longitudinal segment. Yet again, it may be seen as an individual target for each cross-section of the first longitudinal segment of the blade.
According to an advantageous embodiment, the first base part is provided with a linear pre-bend. Thereby, the angular orientation of the base part in relation to the pitch axis may be linearly dependent on the local blade radius. Alternatively, the transverse deviation from the pitch axis may be linearly dependent on the local blade radius. Thereby, it is possible to fit the pre-bend of individual blade segments in order to obtain a pre-bent blade. According to another advantageous embodiment, the first base part is pre-bent, and the airfoil region comprises longitudinal segments comprising base parts with no pre- bending. Thus, the pre-bend may be located in one or two segments of the blade only, for instance the outboard part of the airfoil region and/or in the root region.
Such a base part will in itself have inherent non-optimum aerodynamic properties for a conventional wind turbine blade having a profile, which is twisted in the radial direction of the blade. However, the use of profile with such properties makes it possible to simplify other properties of the blade, such as the twist or the chordal shape of the blade. For example, it is made possible to provide a longitudinal segment having no or a linear twist and/or having a linearly varying chord length in the radial direction of the blade. However, putting such constraints on the design of the base part of the blade will inherently entail that the segment deviates substantially from the near-optimum target axial induction of that segment. In order to compensate for such deviations, it is neces- sary to change the overall inflow properties and the lift coefficient of the segment. However, since the novel profile has a relationship between lift coefficient and angle of attack, which differs significantly from conventional blade profiles, this may be sufficient to even out the deviations or at least change the axial induction towards the target axial induction so that the flow altering devices only have to change the axial induction slightly.
In an example, where the first longitudinal segment has a zero twist or a twist being lower than the near-optimum twist, the novel profile (with the above-mentioned rela- tionship between lift coefficient and angle of attack) compensates for the "lack" of twist, since the angle of attack has to be higher than a conventional profile in order to obtain the right target characteristics, e.g. with respect to the necessary lift coefficient in order to obtain the correct axial induction.
Overall, the shape of the base part can be kept much simpler than the shape of con- ventional, modern wind turbine blades with a length of more than 40 meters. For instance double curvatured blade profiles may be avoided. This also makes the production of mould parts for manufacture of the blades simpler. All in all, the time for initial start-up for developing the design of a new blade type to the product launch of the new blade type may be lowered significantly, and the overall production costs may also be lowered. Thus, according to an advantageous embodiment, the first base part has an inherent non-ideal twist and/or chordal length, and wherein the cross-sectional profile is adapted to compensate for the non-ideal twist and/or chordal length by shifting an axial induction towards a target axial induction. However, putting such a constraint on the design parameters of the blade segment means that the blade segment deviates from the optimum design with respect to aerodynamics. Thus, such a blade segment will inherently be non-ideal with respect to aerodynamics and in particular in relation to an optimum lift coefficient for the segment. This deviation is compensated for by using flow altering devices in order to adjust the design lift to the appropriate near-optimum axial induction as a function of the blade radius. The adjustment of the loading to another blade radius implies the need for use of flow altering devices.
Thus, according to another advantageous embodiment, the first longitudinal segment is provided with a number of first flow altering devices arranged so as to adjust the aero- dynamic properties of the first longitudinal segment to substantially meet a target axial induction factor at a rotor design point.
According to an alternative embodiment, the first base part has a cross-sectional profile having a camber line and a chord line with a chord length, wherein the camber line and the chord line are coinciding over the entire length of the chord. That is, the cross- sectional profile is symmetric about the chord. Such a profile is highly advantageous from a manufacturing point of view. All in all, a first base part comprising: a linear chord, a linear thickness, and a twist, which varies linearly or is constant in the radial direction of the blade, has a number of advantages when designing a modular assembled blade and in respect to manufactur- ing such blades.
According to an advantageous embodiment, the blade and in particular the first base part comprise a shell structure made of a composite material. The composite material may be a resin matrix reinforced with fibres. In most cases the polymer applied is ther- mosetting resin, such as polyester, vinylester or epoxy. The resin may also be a thermoplastic, such as nylon, PVC, ABS, polypropylene or polyethylene. Yet again the resin may be another thermosetting thermoplastic, such as cyclic PBT or PET. The fibre reinforcement is most often based on glass fibres or carbon fibres, but may also be plastic fibres, plant fibres or metal fibres. The composite material often comprises a sandwich structure including a core material, such as foamed polymer or balsawood.
According to an advantageous embodiment, the first longitudinal segment extends along at least 25%, or 30%, or 40%, or 50%, of the airfoil region. The first longitudinal segment may even extend along at least 60%, 70% or 75% of the airfoil region. The extent of the first longitudinal segment may even be up to 100%, when the tip region is considered not being part of the airfoil region. However, the first longitudinal segment may as such be restricted to being part of the airfoil region, in which a near-optimum theoretical aerodynamic performance at the design point may be achieved. This excludes the tip part, the root section, and the transitional section, which due to load and structural considerations always will differ significantly from the near-optimum theoretical aerodynamic performance. Advantageously, the airfoil region may further comprise a longitudinally extending transitional segment. The transitional segment - not to be confused with the transition region of the blade - may extend radially along 5-10% of the airfoil region, and is utilised in the airfoil region to obtain a gradual transition between two longitudinally extending segments according to the invention. Thus, it is recognised that the blade may comprise a number of longitudinally extending sections extending along a substantial part of the blade and a number of transitional segments. As an example, the outer part of the blade may comprise a first longitudinally extending blade segment extending along approximately 40% of the airfoil region, a transitional segment extending along approximately 10% of the airfoil region, a second longitudinally extending blade segment extending along approximately 40% of the airfoil region, and finally a blade tip section extending along approximately 10% of the airfoil region.
According to an advantageous embodiment, the first longitudinal segment is provided at an inboard position of the airfoil region, i.e. in a part nearest the transition region or root region, preferably within two meters of the transition region of the root region, and more preferably adjoining the optional transition region or the root region. The blade may be provided with additional longitudinal segments juxtaposed to the first longitudi- nal segment. All of these should extend along at least 25% of the longitudinal extent of the airfoil region.
Advantageously, the flow guiding means comprises a multi element section, such as a slat, or a flap, i.e. the flow guiding means preferably comprises multi-element parts for changing the profile characteristics of different blade segments. The multi element section is adapted to alter the inflow properties and the loading of the first longitudinal segment of the blade. Preferably, the multi element section alters at least a substantial part of the first longitudinal segment, e.g. along at least 50% of the first longitudinal segment. Thereby, it is possible to change a number of design parameters, such as the design lift, the camber and the angle of attack for the segment, from a base design (of the first base part), which has an inherently non-optimum design from an aerodynamic point of view with respect to such parameters, but which is optimised from a manufacturing point of view. Thus, it is possible to retrofit the multi-element parts to the first base part in order to optimise the aerodynamics. Accordingly, one or more of the num- ber of first flow altering devices may be arranged in the proximity of and/or along the leading edge of the first base part. Further, one or more of the number of flow altering devices may be arranged in the proximity of and/or along the trailing edge of the first base part. Thus, the overall profile may become a multi-element profile having at least two separate elements. Accordingly, the first base part may be constructed as a load carrying part of the blade, whereas the flow guiding means are used to optimise the aerodynamics with respect to matching the local section aerodynamic characteristics to the rotor design point.
Yet again, the flow guiding device may be adjustable in order to passively eliminate variations from inflow variations. The flow altering devices may also comprise a surface mounted element, which alters an overall envelope of the first longitudinal segment of the blade. Advantageously, the surface mounted element is arranged in proximity of the leading edge and/or the trailing edge of the first base part.
According to yet another aspect, the invention provides a wind turbine comprising a rotor including a number of blades, preferably two or three, according to any of the afore- mentioned embodiments. Advantageously, the wind turbine comprises a substantially horizontal axis rotor shaft. Preferably, the wind turbine is operated in an upwind configuration, e.g. according to the "Danish concept".
Equivalently, the invention further provides a method of modifying a blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade comprising: a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being im- pacted by an incident airflow, the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, wherein the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge. The method comprises the steps of: the first base part being designed with an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at a design point deviates from a target axial induction factor, and modifying the first longitudinal segment by providing a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the design point.
Fig. 5 shows a schematic view of a blade consisting of different blade sections, Fig 6a shows a power curve versus wind speed for a wind turbine
Fig. 19a shows the cross-sections of blades provided with multi element profiles and the effect of using such profiles, Figs. 19b-d show different means of locating multi element profiles in relation to a blade cross section,
Fig. 28 shows a blade profile without a double curvature, Fig. 29 shows a graph of an embodiment of a blade having zero camber,
Fig. 45 shows graphs of the inflow angle for transformable blades, Fig. 46 shows graphs of the lift coefficient for transformable blades,
Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position df of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Fig. 4 shows a schematic view of flow velocities and aerodynamic forces at the airfoil profile 50. The airfoil profile is located at the radial position or radius r of the rotor of which the blade is part, and the profile is set to a given twist or pitch angle θ. An axial free stream velocity va, which according to theory optimally is given as 2/3 of the wind velocity vw, and a tangential velocity r ■ ω, which is oriented in a direction of rotation 64 for the rotor, combined form a resultant velocity vr. Together with the chord line 60, the resultant velocity vr defines an inflow angle, φ, from which an angle of attack α can be deducted.
The rotor design for wind turbines of today is a compromise between aerodynamic per- formance and overall wind turbine design loads. Most often, the blade is designed for minimum cost of energy (COE) finding the optimum trade-off between energy yield and turbine loads. This means that the aerodynamic design cannot be looked at as an isolated problem, because it does not make sense to look isolated at maximum energy yield in the event that this may lead to excessive loading. Therefore, classical analytical or semi-analytical methods for designing the blade do not sufficiently apply. 1.1 Blade design parameters
The location of the pitch axis versus blade radius may be defined as x/c(r) and y/c(r), i.e. back-sweep and pre-bending. When the blade is mounted on the rotor, the pre- bending is a pre-deflection of the blade in the direction perpendicular to the rotor plane.
The purpose of pre-bending is to prevent the blade from hitting the tower when the blade is deflected during operation. The prescribed back-sweep allows the placement of the airfoil sections along the length axis of the blade, which influences the section loads throughout the blade.
One important key element in state of the art aerodynamic rotor design methods is the use of pre-designed airfoils. Airfoils are selected for blade stations along the blade radius. The parameters describing each airfoil section are shown in Fig. 4: The lift coeffi- cient 66, c,, the drag coefficient 68, cd, the moment coefficient 75, cm. For individual blade stations, these airfoil characteristics are all described versus the angle of attack, α, which is then determined by the overall blade inflow angle for every section.
Three fundamentally different control schemes exist: 1. Variable rotor speed where the design target point of the rotor may be obtained for the wind speeds where the rotor speed is variable. Usually blade pitch is kept constant.
Figs. 6a-6c show the power characteristics for a typical variable speed and pitch con- trolled (PRVS) wind turbine:
1.3 Rotor design target point Independently on the type of power optimisation, a wind turbine blade is designed for operation at one design target point. For variable rotor speed and/or variable blade pitch, operation at the design target point may be obtained within a wind speed range, whereas for a stall controlled rotor, operation at the design target point appears only at a single wind speed.
The rotor design target point is characterised by the corresponding design tip speed ratio, defined as the ratio between the tip speed and the wind speed, X = r-Ω/V, where Ω is the rotational speed of the rotor. At the design target point, the rotor power coefficient is maximum compared to operating points away from the design target point.
The local section design target point is defined from the velocity triangle for the given section as shown in Fig. 7. Here, the resulting velocity, W, is composed by the axial flow speed, V(1-a), and the tangential flow speed, r-Ω (1+a'). The tangent to the overall flow angle, φ, is equal to the ratio between the axial component and the tangential component. The axial induction factor, a, expresses the percentage reduction of the free flow speed at the rotor plane. The tangential induction factor expresses the percentage rotation of the rotor wake in the rotor plane caused by the rotor. The overall flow angle, φ, is again composed by the local twist angle, Θ, and the local angle of attack, α, as shown in Fig 4.
When knowing the local chord c, and local twist Θ as well as the airfoil section force coefficients versus the local angle of attack α, it is possible to use the so called blade element momentum method (BEM) to solve for the equilibrium between the overall gross flow through the rotor annulus covered by the blade section and the local forces on each of the blades. The resulting normal force perpendicular to the rotor plane and the tangential force parallel to the rotor plane may be calculated. Through this calcula- tion procedure, the induction factors are determined and when operating at the rotor design target point, the induction factor is then denoted as the target induction factor.
A simple method exists for determining the exact optimum induction and thereafter lo- cal chord and twist for optimum aerodynamic performance. An example of such a method is the method by Glauert published with the BEM method (Glauert, H. Airplane propellers in Aerodynamic Theory ed. Durand, W. F. Dower Publications, Inc. New York).
where as previously mentioned, x=Ω r/V is the tip speed ratio, V is the design point wind speed, X is the tip speed based on R and Φ is the local inflow angle, and a is the axial induction. When defining an aerodynamic blade shape the first step is to choose the number of blades and the design tip speed ratio. The ideal rotor loading defined as the chord length multiplied by the lift coefficient (c- c,) and the inflow angle, Φ, can then be found versus radius. On basis of the ideal rotor loading, the target loading may be decided on taking into account loads and practical limitations.
Next, selecting the airfoils for the individual blade sections and knowing the flow angle makes it possible to decide the blade twist. This is commonly chosen so that the airfoil lift-to-drag ratio is optimal on as large a part of the blade as possible to maximize the rotor power coefficient. The blade operating lift coefficient c,;O is then typically the airfoil design lift coefficient cid and the chord can then be derived from the target loading. However on parts of the blade there will be a difference between the blade operating lift coefficient c,o versus the airfoil design lift coefficient cld due to considerations on loads, manufacture, etc. When there is a difference, the operating lift coefficient will not lead to optimum lift-to-drag as indicated in Fig. 16 and the operating angle of attack, α0 will not be equal to the airfoil design angle of attack, αd.
The BEM method also reveals that an axial induction of 1/3 unfortunately is associated with a high thrust force on the rotor and that thrust and thereby loads can be reduced significantly with only little reduction in rotor power. This is because designing for the aerodynamic optimum in a single point does not take into account off-design operation nor loads and thereby minimum cost of energy. To reduce loads the axial induction is often reduced compared to the optimum value of 1/3. On the other hand when including also off-design operation in the design problem, such as operation close to power control, there may be a required minimum value for the target induction factor to prevent premature stall on the blades leading to unnecessary noise and power loss. Hence, for a modern rotor the target induction factor is not necessarily identical to the aerodynamic optimum induction and there is not a single optimum for the target induction versus blade radius, since such an optimum depends on numerous factors. In Figs. 8a and 8b the ideal values (dashed lines) for loading (c- C/) and inflow angle, Φ, are shown together with the real target values (full drawn lines) for inflow and loading of a typical wind turbine blade. It can be seen that there is a nearby match between the two curves over a large part of the blade but that there are also discrepancies. It is seen that the target value especially deviates from the ideal values for low values of r, i.e. near the blade root. This is mainly due to structural considerations as explained in relation to Figs. 2 and 5. Furthermore, it appears clearly from Fig. 8a and Fig. 8b that since loading and inflow angle varies non-linearly with blade radius, this will also be the case for both the chord and twist - not only for the ideal blade but also for a typical commercial blade.
In accordance with blade design, a blade may be divided into four different regions as shown in Figs. 2 and 5: 1. The blade root region 30 next to the hub, which is predominantly circular.
The invention primarily relates to a different design of the airfoil shaped part 34' of the blade, see Fig. 5. In the following, blades according to the invention will sometimes be referred to as transformable blades. Fig. 9 shows a first embodiment of a wind turbine blade according to the invention. Similar to the conventional method of designing a wind turbine blade, the blade is divided into a root region 130, a transition region 132, and an airfoil region 134. The airfoil region comprises a blade tip part 136 and a first longitudinal section 140 of the blade. The first longitudinal section of the blade is divided into a first base part 141 and a number of flow altering devices 146-149. The first base part 141 has a profile, which has a simplified structure with respect to for instance modularity of blade parts and/or manufacturing of the first base part 141 , and which at the rotor design point in itself deviates substantially from the target axial induction factor and/or the target loading. Therefore, the first longitudinal section 140 is provided with the flow altering devices, which are here depicted as a first slat 146 and a second slat 147, as well as a first flap 148 and a second flap 149. Although the use of such flow altering devices is highly advantageous in order to obtain the target axial induction factor and the target loading, the invention is not restricted to such flow altering devices only. The first longitudinal section 140 extends along at least 20% of the longitudinal length of the airfoil region 134.
Fig. 10 shows a second embodiment of a wind turbine blade according to the invention. Similar to the conventional method of designing a wind turbine blade, the blade is divided into a root region 230, a transition region 232, and an airfoil region 234. The airfoil region comprises a blade tip part 236, a first longitudinal section 240, and a second longitudinal section 242. The first longitudinal section 240 of the blade is divided into a first base part 241 and a number of first flow altering devices 246. The second longitudinal section 242 of the blade is divided into a second base part 243 and a number of second flow altering devices 248. The first base part 241 and the second base part 243 have profiles, which have a simplified structure with respect to for instance modularity of blade parts and/or manufacturing of the base parts 241 , 243, and which at the rotor design point in itself deviates substantially from the target axial induction factor and/or the target loading. Therefore, the longitudinal sections are provided with the flow alter- ing devices, which are here depicted as a first slat 246 and a first flap 248, however; the flow altering devices are not restricted to such flow altering devices only. The first longitudinal section 240 and the second longitudinal section 242 both extend along at least 20% of the longitudinal length of the airfoil region 234.
Fig. 1 1 shows a third embodiment of a wind turbine blade according to the invention, wherein like reference numerals refer to like parts of the second embodiment shown in Fig. 10. Therefore, only the difference between the two figures is explained. The third embodiment differs from the second embodiment in that the airfoil region 334 further comprises a transition section 344 arranged between the first longitudinal section 340 and the second longitudinal section 342. The transition section 344 comprises a transi- tion base part 345, which is formed by morphing from the end profiles of the first base part 341 and second base part 343, respectively. Accordingly, the transition base part 345 also has a profile shape, which at the rotor design point in itself deviates substantially from the target axial induction factor and/or the target loading. Consequently, the transition section 344 is also provided with a number of flow altering devices 346, 348.
Fig. 12 shows a first situation illustrating the above mentioned deviation. As explained in section 1.4, the local section design target point is defined from the velocity vector triangle, where the resulting velocity vιnflow is composed by the axial flow speed, Vwιnd(1- atargetX and the tangential flow speed, r-ω (1 +a'), see also Fig. 12a. This condition is only met at the rotor design point, when the inflow angle is O1. At the rotor design point, the local section has an operational lift coefficient q and an operational drag coefficient cd. The resultant aerodynamic forces may as previously explained be divided into a tangential force T, which is oriented in the rotational plane of the rotor and a loading or thrust, which is the normal force Ntarget oriented normally to the rotor plane 64'.
For the given profile of the section having a given local chord length c, the target conditions for achieving the target axial induction factor atarget and the target normal load Ntar get for the local blade profile at the rotor design point is met only, when the local twist angle is equal to a target twist θi and the angle of attack is equal to α-i.
However, the local blade profile for the base part has an actual twist Q2, which is lower than the target twist θi. Consequently, the inflow angle is shifted to an altered angle O2, which is lower than O1. Furthermore, the angle of attack is changed to an altered angle of attack α2, which is larger than Ot1. Consequently, the two shown vector triangles are as shown in Fig. 12b shifted and the blade section obtains an inflow condition having an altered resultant velocity vector Vιnf|Ow2, at which an actual axial induction factor a2 becomes larger than the target axial induction factor atarget- Further, the lift coefficient is shifted to an altered lift coefficient Q2, and an altered drag coefficient cd2. Consequently, the normal load is shifted to an actual normal load N2, which is larger than the target normal load Ntarget- Consequently flow altering devices are needed in order compensate for the altered inflow conditions and normal load.
In order to obtain the target axial induction factor atarget, the inflow angle must be shifted back to O1 as shown in Fig. 12c. Consequently, the compensated angle of attack must equal 0,3 = O1 - θ2. At this angle of attack, the flow altering devices (here depicted as a flap) must alter the drag coefficient and lift coefficient to altered values cd3 and Q3, at which the resultant normal load becomes equal to the target normal load Ntarget- Thus, the flow altering devices are used to reduce the axial induction factor from a2 to atarget, and reduce the load from N2 to Ntarget-
Fig. 13 shows a similar situation, but where the local blade profile for the base part having a given local chord length c has an actual twist θ2, which is higher than the target twist G1 (as shown in Fig. 13b). Consequently, the inflow angle is shifted to an altered angle O2, which is larger than O1. Furthermore, the angle of attack is changed to an al- tered angle of attack α2, which is smaller than (X1. Consequently, the two shown vector triangles are as shown in Fig. 12b shifted and the blade section obtains an inflow condition having an altered resultant velocity vector vιnf|Ow2, at which an actual axial induction factor a2 becomes smaller than the target axial induction factor atarget- Further, the lift coefficient is shifted to an altered lift coefficient Q2, and an altered drag coefficient cd2. Consequently, the normal load is shifted to an actual normal load N2, which is smaller than the target normal load Ntarget- Consequently flow altering devices are needed in order to compensate for the altered inflow conditions and normal load.
In order to obtain the target axial induction factor atarget> the inflow angle must be shifted back to O1 as shown in Figs. 13a and 13c. Consequently, the compensated angle of attack must equal α3 = O1 - θ2. At this angle of attack, the flow altering devices (here depicted as a flap) must alter the drag coefficient and lift coefficient to altered values cd3 and C|3, at which the resultant normal load becomes equal to the target normal load Ntarget- Thus, the flow altering devices are used to increase the axial induction factor from a2 to atarget, and increase the load from N2 to Ntarget-
Fig. 14 yet again shows a similar situation. For the given profile of the section having a given pitch angle G1 and angle of attack Ot1, the target conditions for achieving the tar- get axial induction factor atarget and the target normal load Ntargetfor the local blade profile at the rotor design point are only met, when the chord length is equal to a target chord C1 (as shown in Fig. 14a).
However, the local blade profile for the base part has an actual chord length C2, which is lower than the target chord C1. Consequently, the inflow angle is shifted to an altered angle O2, which is higher than O1. Furthermore, the angle of attack is changed to an altered angle of attack α2, which is larger than Ot1. Consequently, the two shown vector triangles are as shown in Fig. 14b shifted and the blade section obtains an inflow condition having an altered resultant velocity vector VιnfiOw2, at which an actual axial induc- tion factor a2 becomes smaller than the target axial induction factor atarget. Further, the lift coefficient is shifted to an altered lift coefficient Q2, and an altered drag coefficient cd2. Consequently, the normal load is shifted to an actual normal load N2, which is smaller than the target normal load Ntarget- Consequently flow altering devices are needed in order compensate for the altered inflow conditions and normal load. In order to obtain the target axial induction factor atarget, the inflow angle must be shifted back to O1 as shown in Fig. 14c. Consequently, the compensated angle of attack must equal 0,3 = Φ1 - Θ2. At this angle of attack, the flow altering devices (here depicted as a flap) must alter the drag coefficient and lift coefficient to altered values cd3 and Q3, at which the resultant normal load becomes equal to the target normal load Ntarget- Thus, the flow altering devices are used to increase the axial induction factor from a2 to atarget, and increase the load from N2 to Ntarget-
Fig. 15 shows yet again a similar situation, but where the local blade profile for the base part having a given twist angle Q2 has an actual chord C2, which is larger than the target chord C1 (as shown in Fig. 15b). Consequently, the inflow angle is shifted to an altered angle Φ2, which is lower than O1. Furthermore, the angle of attack is changed to an altered angle of attack α2, which is lower than Ot1. Consequently, the two shown vector triangles are as shown in Fig. 15b shifted and the blade section obtains an inflow condition having an altered resultant velocity vector vιnflow2, at which an actual axial induction factor a2 becomes larger than the target axial induction factor atarget. Further, the lift coefficient is shifted to an altered lift coefficient cl2, and an altered drag coefficient cd2. Consequently, the normal load is shifted to an actual normal load N2, which is larger than the target normal load Ntarget- Consequently flow altering devices are needed in order to compensate for the altered inflow conditions and normal load.
In order to obtain the target axial induction factor atarget, the inflow angle must be shifted back to O1 as shown in Figs. 15a and 15c. Consequently, the compensated angle of attack must equal α3 = O1 - θ2. At this angle of attack, the flow altering devices (here depicted as a flap) must alter the drag coefficient and lift coefficient to altered values cd3 and C|3, at which the resultant normal load becomes equal to the target normal load Ntarget- Thus, the flow altering devices are used to decrease the axial induction factor from a2 to atarget, and decrease the load from N2 to Ntarget-
Fig. 17 shows a first example of flow altering devices 80 for compensating for off-target design parameters of the base part of the respective longitudinal section of the blade. In this embodiment, the flow altering means consists of a number of ventilation holes 80 for blowing or suction between an interior of the blade and an exterior of the blade. The ventilation holes are advantageously applied to the suction side of the blade as shown in Figs. 17a and 17b. The ventilation holes 80 can be utilised to create a belt of attached flow. Air vented from the ventilation holes 80 may used to energise and re- energise the boundary layer in order to maintain the flow attached to the exterior surface of the blade as shown in Fig 17b. Alternatively, the ventilation holes may be used for suction as shown in Fig. 17a, whereby the low momentum flow in the boundary layer is removed and the remaining flow thereby reenergised and drawn towards the surface of the blade. Alternatively, the ventilation holes may be used to generate a pulsating flow, e.g. as a synthetic jet. Despite not generating a flow, this transfers momentum to the flow and thereby reenergises the boundary layer and alters flow separation. Examples of such embodiments are shown in Figs. 17c and 17d, in which the ventila- tion holes are provided with membranes. The membranes may be provided near the exterior surface of the blade as shown in Fig. 17d or near the interior surface of the blade as shown in Fig. 17c.
Fig. 18 shows a second example of flow altering devices of flow altering devices 180, 181 , 182 for compensating for off-target design parameters of the base part of the blade. In this embodiment, the flow altering means consists of a number of surface mounted elements. Fig. 18a shows a first embodiment, in which a first trailing edge element 180 is mounted near the trailing edge of the blade on the suction side of the blade, a second trailing edge element 181 is mounted near the trailing edge of the blade on the pressure side of the blade, and a leading edge element 182 is mounted near the leading edge of the blade on the pressure side of the blade. Fig. 18b shows a second embodiment, in which only a first trailing edge element is utilised on the suction side of the blade.
The full drawn line in Fig. 18c shows the relationship between the lift coefficient and the inflow angle (or alternatively the angle of attack) for the basic airfoil without the use of surface mounted element. By utilising the leading edge element 182 and the second trailing edge element 181 on the pressure side of the blade, the effective camber of the airfoil is increased and the operating lift coefficient at the rotor design point is in- creased. The maximum lift coefficient is also increased. By utilising the first trailing edge element 180 on the suction side of the blade, the camber of the airfoil is reduced and the operating lift coefficient at the rotor design point as well as the maximum lift coefficient is decreased.
Fig. 19 shows the effect of using multi-element airfoils, such as slats or flaps, as flow guiding devices. The depicted graph shows the relationship between the lift coefficient and the inflow angle (or alternatively the angle of attack) for the basic airfoil without the use of multi-element airfoils. By utilising a trailing edge flap oriented towards the pressure side of the blade, the graph is shifted towards lower angles of attack. By utilising a trailing edge flap oriented towards the suction side of the blade, the graph is shifted towards higher angles of attack. By using a slat near the suction side of the blade, the lift coefficient is increased, and further the maximum lift coefficient is found at a slightly higher angle of attack. By using a slat near the suction side of the blade and a flap oriented towards the pressure side of the blade, the lift coefficient is increased, and fur- ther the maximum lift coefficient is found at a lower angle of attack. By using a slat near the suction side of the blade and a flap oriented towards the suction side of the blade, the lift coefficient is increased, and further the maximum lift coefficient is found at a higher angle of attack.
Slats and flaps may be implemented in various ways. A slat may for instance be con- nected to the first base part of the blade via a connection element as shown in Fig.
19b. The slat may be connected to the first base part in such a way that it is rotational and/or translational movable in relation to the first base part. Likewise a flap may be provided as a separate element as shown in Fig. 19c, which may be moved rotational and/or translational in relation to the first base part. Thus, the blade profile is a multi element profile. Alternatively, the flap may be implemented as a camber flap as shown in Fig. 19d, which can be used to change the camber line of the blade profile.
Fig. 20 shows another example of flow altering devices 280 for compensating for off- target design parameters of the base part of the blade. In this embodiment, the flow al- tering means comprises a device attached to the pressure side at the trailing edge, in this case a Gurney flap 280 as shown in Fig. 20a. Other attachments with similar flow altering means are a triangular wedge or a rip forming an angle of more than 90 degrees with the surface of the profile. The full drawn line in Fig. 20b shows the relationship between the lift coefficient and the inflow angle (or alternatively the angle of at- tack) for the basic airfoil without the use of a surface mounted element. By utilising the Gurney flap, the operating lift coefficient at the rotor design point is increased as well as the maximum lift coefficient, which is also increased as shown as the dashed line in Fig. 20.
3 Simplified Base Parts of Blade In this section, a number of simplified base part structures for transformable blades are described.
Therefore, from a design and manufacturing point of view it would be advantageous to obtain a base part of the blade having a simplified twist, such as a linearly dependent twist or a reduced twist compared to an optimum twist. Such simplified twist makes it feasible to achieve a modular blade design, in which the base part with the non- optimum twist can be used for several different blade types and blade lengths. Thus, it is possible to reuse the base part of an existing blade further outboard on a larger/longer blade, or alternatively reuse the base part of an existing blade further inboard on a smaller/shorter blade. All in all, it is possible to make a blade design in such a way that the blade design of the airfoil region is put together from pre-designed sec- tions and that blades of different lengths can be composed partly from sections already existing from previous blades. However, putting such a constraint on the blade design implies the need for using flow altering devices in order to compensate for not being able to operate at the target design ideal twist for the different blade sections as explained in subsection 2.1.
Fig. 23a shows graphs of an average angle of attack 78 for the blade as a function of the radial distance r from the hub of the rotor. Fig. 23a also shows a graph of an opti- mum angle of attack 76 of the blade without flow altering devices as a function of the radial distance from the hub. It can be seen that the average angle of attack 78 is higher than the optimum angle of attack 76, which clearly indicates that the blade does not have an optimum blade twist. Therefore, the blade can be provided with flow altering devices as for instance shown in Figs. 17-22 in order to shift the optimum angle of attack with a shift angle Δα, thereby shifting the optimum angle of attack towards the average angle of attack for a given radial distance rfrom the hub.
Fig. 23b shows a graph of the shift angle Δα as a function of the radial distance from the hub. It can be seen that the shift angle Δα is continuously decreasing with increas- ing distance rfrom the hub. Figs. 23c and 23d illustrate the effect of providing the blade with flow altering devices for the outer part 44 and the inner part 42 of the blade, respectively. Fig. 23c shows graphs of the relationship between the drag coefficient and the lift coefficient as well the relationship between the angle of attack and the lift coefficient. The graphs are ex- amples of design parameters for the blade at a given radial distance from the hub falling within the outer part 44 of the blade. The design point is depicted with a dot and is chosen based on an optimum relationship between the lift coefficient and the drag coefficient, e.g. by maximising the lift-to-drag ratio. By providing the blade with flow altering devices, the graph showing the relationship between the lift coefficient and the an- gle of attack is shifted towards higher angles, thereby compensating for the "missing" twist of the outer part 44 of the blade.
Yet again, as shown in Fig. 30, the profile may for at least a part of the longitudinal section be simplified even further to a symmetrical profile 350 having a chord 360 and camber 362, which are coincident. Such a blade profile has a relationship between lift coefficient and inflow angle, which crosses the origin of the coordinate system as shown in Fig. 29. This means that the graph is shifted towards higher inflow angles as compared to conventional non-symmetric blade profiles with a positive camber. This also implies that a particular lift coefficient may be obtained at a higher angle of attack than for the conventional blade profile. This is advantageous for embodiments having a reduced twist compared to an optimum twist as explained in subsection 3.1. In other words, the reduced twist and the symmetric profile at least partially compensate for each other. This compensation may be exploited even further by providing at least a part of the longitudinal section with a profile 450 as shown in Fig. 32 having a "negative camber", i.e. a blade where the camber 462 is located closer to the pressure side 452 of the blade than the suction side 454 of the blade (or equivalently, where the camber 462 is located below the chord 460). A blade section has a negative lift coefficient for an incident airflow at an angle of attack of 0 degrees, i.e. the graph illustrating the relationship between lift coefficient and angle of attack is shifted even further towards larger inflow angles. This in turn means that a particular lift coefficient may be obtained at an even higher angle of attack. The use of profiles having a negative camber may be advantageous especially for blades having a very low twist or no twist, since such blades have blade sections, in which the operational angle of attack at the rotor design point is very high. This is particularly relevant for the inboard part of the airfoil region and the transition region.
However, the camber 462 need not locally be located nearer the pressure side of the blade than the suction side of the blade along the entire chord of the profile as shown in Fig. 32. As shown in Fig. 33, it is also possible to provide a blade section with profile 550 having a negative camber 562, in which a part of the camber is closer to the suc- tion side 554 of the blade than the pressure side of the blade 552 (or above the chord 560) as long as the camber 562 on average is closer to the pressure side 552 than the suction side of the blade 554.
4 Modularity and reuse of blade sections As previously mentioned, the use of a simplified base part of the longitudinal section of the blade makes it possible to use that base part for several different types of blades and use flow altering devices to compensate for the off-design characteristics of the base part.
Fig. 34 illustrates this principle. A wind turbine blade 410 is divided into a root region 430, a transition region 432, and an airfoil region 434. The airfoil region 434 comprises a blade tip part 436, a first longitudinal section 440, and a second longitudinal section 442. The first longitudinal section 440 of the blade is divided into a first base part 441 and a number of first flow altering devices 446. The second longitudinal section 442 of the blade is divided into a second base part 443 and a number of second flow altering devices 448. The first base part 441 and the second base part 443 have profiles, which have a simplified structure with respect to for instance modularity of blade parts and/or manufacturing of the base parts 441 , 443, and which at the rotor design point in itself deviate significantly from the target axial induction factor and/or the target loading. The base parts 441 are here depicted as having linearly dependent chord lengths, but ad- vantageously, the sections also have a linearly dependent thickness and linearly dependent twist or no twist. Therefore, the longitudinal sections are provided with the flow altering devices, which are here depicted as a first slat 446 and a first flap 448, however; the flow altering devices are not restricted to such flow altering devices only. The first longitudinal section 440 and the second longitudinal section 442 both extend along at least 20% of the longitudinal length of the airfoil region 434. The first longitudinal section or base part is located in a first radial distance r-,.
The first base part 441 is reused for a second blade 410', which also comprises a root region 430', a transition region 432', and an airfoil region 434'. The airfoil region 434' comprises a blade tip part 436', a first longitudinal section 440', a second longitudinal section 442' having a second base part 443', and a third longitudinal section or transition section 445' located between the first longitudinal section 440' and the transition region 432'. The first longitudinal section and first base part 441 of the second blade 410' are located at a second radial distance r2. Therefore, the inflow conditions for the first base part 441 are different from the first blade 410 and the second blade 410'. Further, the target chord lengths (for base parts without flow altering devices) need to be different in order obtain the target axial induction factor and the target normal load. Consequently, the second blade 410' needs different flow altering devices 446', 448' than the first blade 410 in order to compensate for the off-design conditions.
In principle, a first blade may be reused entirely for a second blade, for instance by providing the first blade with a hub extender as shown in Fig. 35. In this situation, substantially the entire hatched part of the second blade be encumbered with off-design conditions and a majority of this section will need the use of flow altering devices, ad- vantageously both the airfoil region and the transition region of the second blade. 5 Operation of a wind turbine with transformable blades
- the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, characterised in that - the first base part has an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at a design point deviates from a target axial induction factor, and wherein
- the first longitudinal segment is provided with a number of first flow altering de- vices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the design point.
4. A blade according to any of the preceding claims, wherein the induction factor of the first base part without flow altering means deviates from the target axial induction factor along substantially the entire longitudinal extent of the first longitudinal segment.
5. A blade according to any of the preceding claims, wherein the target axial induc- tion factor is close to the aerodynamic optimum target axial induction factor.
6. A blade according to any of the preceding claims, wherein the target axial induction factor lies in the interval between 0.25 and 0.4, or between 0.28 and 0.38, or between 0.3 and 0.33
7. A blade according to any of the preceding claims, wherein the induction factor of the first base part without flow altering devices at the design point deviates at least 5%, or 10%, or 20% or 30% from the target axial induction factor.
8. A blade according to any of the preceding claims, wherein the first base part without flow altering devices at the design point further deviates from a target loading, and wherein the first flow altering devices are further arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target loading at the design point.
10. A blade according to any of the preceding claims, wherein the first longitudinal segment in the radial direction is divided into:
- a plurality of radial sections, each radial section having an individual average operating angle of attack for the design point and having a sectional airfoil shape, which without the first flow altering devices has a sectional optimum angle of attack, and wherein - the first flow altering devices are adapted to shift the optimum angle of attack of the sectional airfoil shape towards the average operating angle of attack for the radial section.
1 1. A blade according to any of the preceding claims, wherein the first base part has a twist, which is non-ideal along substantially the entire longitudinal extent of the first longitudinal segment.
12. A blade according to any of the preceding claims, wherein the first base part has a twist of less than 8 degrees.
13. A blade according to any of the preceding claims, wherein the first base part has a substantially constant twist.
14. A blade according to any of the preceding claims, wherein the first base part has a twist being linearly dependent on a radial position.
15. A blade according to any of the preceding claims, wherein the first base part has an inherent twist angle so that the first base part without flow altering devices at the ro- tor design point has an inflow angle, which is lower than the optimum inflow angle along the entire longitudinal extent of the first longitudinal segment.
16. A blade according to any of claims 1-14, wherein the first longitudinal segment has an inherent twist angle so that the first base part without flow altering devices at the rotor design point comprises a first segment, in which the inflow angle is lower than the optimum inflow angle, and a second segment, in which the inflow angle is higher than the optimum inflow angle.
17. A blade according to any of the preceding claims, wherein the root mean square difference over the longitudinal extent of the first longitudinal section between the average inflow angle and the optimum inflow of attack at the design point is more than 1 degree, or more than 2 degrees, or more than 2.5 degrees for the first longitudinal segment without flow altering devices.
- a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trail- ing edge, the profiled contour generating a lift when being impacted by an incident airflow,
- the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region be- tween the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, characterised in that
- the first base section being formed with an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at the rotor design point deviates from a target axial induction factor, and wherein
- the first base section is provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the rotor design point.
- designing the first base part with an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction factor of the first base part without flow altering devices at the rotor design point deviates from a target axial induction factor, and
- the first base part being designed with an inherent non-ideal twist, such as no twist, or a reduced twist compared to a target blade twist, so that an axial induction fac- tor of the first base part without flow altering devices at a design point deviates from a target axial induction factor, and
PCT/EP2010/056793 2009-05-18 2010-05-18 Wind turbine blade with base part having inherent non-ideal twist WO2010145902A1 (en)
EP20090160477 EP2253834A1 (en) 2009-05-18 2009-05-18 Wind turbine blade with base part having inherent non-ideal twist
EP09160477.7 2009-05-18
US13320977 US8899922B2 (en) 2009-05-18 2010-05-18 Wind turbine blade with base part having inherent non-ideal twist
EP20100723008 EP2432995A1 (en) 2009-05-18 2010-05-18 Wind turbine blade with base part having inherent non-ideal twist
CN 201080032424 CN102459878B (en) 2009-05-18 2010-05-18 Wind turbine blade with base part having inherent non-ideal twist
WO2010145902A1 true true WO2010145902A1 (en) 2010-12-23
ID=41361332
PCT/EP2010/056793 WO2010145902A1 (en) 2009-05-18 2010-05-18 Wind turbine blade with base part having inherent non-ideal twist
US (1) US8899922B2 (en)
EP (2) EP2253834A1 (en)
CN (1) CN102459878B (en)
WO (1) WO2010145902A1 (en)
DE102013206437A1 (en) * 2013-04-11 2014-10-16 Senvion Se Rotor blade of a wind turbine and wind turbine
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FR3018867A1 (en) * 2014-03-18 2015-09-25 Hassan Zineddin Structure and method of fixing wind turbine blades for avoiding overspeed formatting the wind turbine
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