Blade design method and blade for a wind turbine generator system

Abstract

The application provides a blade design method and a blade for a wind turbine unit. According to the blade design method, the whole blade or a certain section of the blade is taken as a design section along the blade spanwise direction, the blade chord length is increased, the blade torsion angle is reduced, or the blade relative thickness is reduced by reducing the design lift coefficient, so as to reduce the possibility of blade stall. According to the design method of the application, the possibility of blade stall is reduced, the aerodynamic performance of the blade is improved, and the aerodynamic noise of the blade is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wind power generation technology, and particularly relates to a blade design method and a blade for wind turbine generator sets. Background Technology

[0002] A wind turbine is an aerodynamic device that relies on the lift generated by its blade airfoils. When air flows over the airfoil, a negative pressure is created on the upper surface (suction surface) and a positive pressure is created on the lower surface (pressure surface). The pressure difference between the upper and lower surfaces generates lift, which drives the rotor to rotate and converts wind energy into electrical energy.

[0003] The lift of a blade airfoil increases linearly with the angle of attack, but after reaching a certain critical value, the lift suddenly decreases while the drag increases significantly, indicating a stall. Wind turbine blades should be kept away from stall or flow separation conditions as much as possible, because stall not only leads to a loss of power generation performance but can also damage related components and even the entire turbine, thus causing safety issues. There are many causes of stall, such as decreased air density, poor blade surface conditions, sudden changes in wind speed, direction, and turbulence, improper turbine control, and the blade's own design.

[0004] Existing blade design often prioritizes cost and weight, with insufficient understanding and attention paid to airfoil aerodynamic performance, blade output performance, and stall itself. Coupled with the aforementioned stall factors, this can lead to blades stalling immediately upon installation or stalling after a few months of operation. In some cases, the power curves of certain units appear good, but noise tests reveal localized stalling on the blades.

[0005] When severe blade stall is detected, the blades need to be redesigned to obtain blades that meet the unit's operating performance requirements. Summary of the Invention

[0006] One of the main objectives of this invention is to provide a blade design method and blades for wind turbine generators to reduce the possibility of blade stall.

[0007] According to one aspect of the present invention, a blade design method is provided, in which the entire blade or a segment thereof is taken as a design segment along the blade spanwise, and the blade chord length is increased, the blade twist angle is reduced, or the relative thickness of the blade is reduced by decreasing the design lift coefficient, thereby reducing the possibility of blade stall.

[0008] According to one aspect of the present invention, the blade design method includes the following steps: determining the airfoil of each design segment of the blade; determining a plurality of design points along the blade spanwise; setting the design lift coefficient of the plurality of design points such that the design lift coefficient of the plurality of design points is lower than a predetermined value than a reference design lift coefficient; and performing curve fitting on the design lift coefficient of the plurality of design points to obtain the design lift coefficient curve of the blade.

[0009] According to one aspect of the invention, the airfoil of each design segment of the blade is determined based on a reference blade, wherein the reference blade is a blade that stalls at a predetermined position in the spanwise direction under standard design air density ±0.15 kg / m³, and the predetermined position is the standard airfoil position.

[0010] According to one aspect of the present invention, the reference lift coefficient refers to the design lift coefficient corresponding to the reference blade at the plurality of design points, wherein the design lift coefficient at the plurality of design points is 0 to 0.5 lower than the reference lift coefficient.

[0011] According to one aspect of the present invention, the blade includes a common-mode section co-mode with the reference blade and a new design section, wherein in the common-mode section, the design lift coefficient of the plurality of design points is set to be the same as the reference lift coefficient, and in the new design section, the design lift coefficient of the plurality of design points is set to be 0.001 to 0.5 lower than the reference lift coefficient.

[0012] According to one aspect of the invention, in the new design section, the design lift coefficient of the plurality of design points is set to be 0.01 to 0.05 lower than the reference lift coefficient.

[0013] According to one aspect of the invention, the reference design lift coefficient includes the maximum lift coefficient corresponding to the respective blade airfoil.

[0014] According to one aspect of the invention, when the blade is divided into multiple design segments along the spanwise direction, curve fitting is performed in one of the following ways: (a) each segment is a design segment of 2m to 10m, and each segment is fitted with a function of no more than the fourth power, with a goodness of fit of no less than 0.98; (b) each segment is a design segment of 10m to 20m, and each segment is fitted with a function of no more than the sixth power, with a goodness of fit of no less than 0.97; (c) each segment is a design segment of 20m to 50m, and each segment is fitted with a function of no more than the tenth power, with a goodness of fit of no less than 0.95.

[0015] According to one aspect of the invention, the blade airfoil is a laminar flow airfoil or a high-lift airfoil.

[0016] According to one aspect of the invention, the plurality of design points include at least one of the locations corresponding to relative thicknesses of 30%, 25%, 24%, 21%, and 18%.

[0017] According to one aspect of the invention, the blade is longer than the reference blade and includes an extended section, wherein the design lift coefficient of a plurality of design points on the extended section is determined based on the maximum lift coefficient CLmax of the airfoil corresponding to the extended section.

[0018] According to one aspect of the invention, at least two design points are selected within a 2-8m region near the blade tip in the common mode section.

[0019] According to one aspect of the invention, the design lift coefficient of the 10% section at the tip of the blade is 0 to 2 lower than the local maximum lift coefficient CLmax, and the design lift coefficient at the tip is 0.

[0020] According to another aspect of the present invention, a blade for a wind turbine generator is provided, the blade being designed using the blade design method described above, and the airfoil of the blade being a DU series airfoil.

[0021] According to one aspect of the invention, at a blade span of 40-50m, the design lift coefficient of the blade is 1.0-1.2.

[0022] According to one aspect of the invention, the blade chord length is 1.3 to 1.4 m.

[0023] According to one aspect of the invention, the twist angle of the blade is -2 to 0 degrees.

[0024] According to one aspect of the invention, the relative thickness of the blade is 20-30%.

[0025] This invention, through a thorough understanding of the aerodynamic performance of airfoils, designs a reference blade by truncating and extending it in the middle. The design point is selected at the angle of attack far from the stall point. By increasing the blade chord length and reducing the twist angle, the stall degree of the extended blade is greatly reduced. This blade shape design concept can be applied to all blade designs. Attached Figure Description

[0026] The above and / or other objects and advantages of the present invention will become more apparent from the following description of embodiments in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a comparative example diagram of the design lift coefficient curve of a new blade according to an embodiment of the present invention and the design lift coefficient of a reference blade;

[0028] Figure 2This is an example of fitting the lift coefficient curve of a new blade according to an embodiment of the present invention;

[0029] Figure 3 This is an example of comparing the chord length of a new blade and a reference blade according to an embodiment of the present invention;

[0030] Figure 4 This is an example of comparing the torsion angle of a new blade and a reference blade according to an embodiment of the present invention.

[0031] Figure 5 This is an example diagram of the lift coefficient curves of a new blade according to an embodiment of the present invention under different incoming wind speeds. Detailed Implementation

[0032] Example embodiments will now be described more fully with reference to the accompanying drawings. However, it should not be construed that the embodiments of the invention are limited to those described herein. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed descriptions will be omitted.

[0033] When the design lift coefficient of a blade is close to its maximum lift coefficient CLmax, there is a risk of stall. For example, under conditions of high turbulence or changes in basic operating conditions, the blade can easily enter a stall state or experience localized stall. Therefore, the closer the design lift coefficient of a blade is to its maximum lift coefficient CLmax, the more prone it is to stall, and the narrower its applicable air density range.

[0034] Furthermore, new blades have a relatively smooth surface, resulting in a relatively high maximum lift coefficient (CLmax). However, as the blade surface becomes contaminated over time, the CLmax decreases. Therefore, when determining the design lift coefficient of a blade, it is necessary to consider not only the maximum lift coefficient CleanCLmax for a smooth blade surface but also the maximum lift coefficient RoughCLmax for a rough blade surface. A certain distance must be maintained between the design lift coefficient and these two maximum lift coefficients, especially a certain difference from RoughCLmax, to ensure a safe operating margin for the blade. Thus, a certain distance (difference) is required between the design lift coefficient and the maximum lift coefficient RoughCLmax to reduce the risk of blade stall.

[0035] When a blade stalls or is at risk of stalling, it needs to be redesigned. For example, when the blade's spanwise position is within ±0.15 kg / m² of the standard air density... 3 If a stall occurs under certain conditions, the blade is identified as a stall blade and needs to be redesigned. The predetermined position mentioned here refers to the standard airfoil position.

[0036] In addition, other methods can be used to determine whether a blade is at risk of stall. For example, if the difference between the blade's design lift coefficient and its corresponding maximum lift coefficient (CleanCLmax) is less than a predetermined value (e.g., less than 0.3), the blade can be considered to be at risk of stall. Another example is when the blade is designed for an air density of 1.0 kg / cm³. 3 If the leaf is in an air density of 0.9 kg / cm³ 3 If stalling occurs, the blade needs to be redesigned. However, the present invention is not limited to the above example; the conditions under which a blade is at risk of stalling can be determined based on the actual situation.

[0037] In this invention, blades that have a risk of stalling or have stalling problems are identified as stall blades (also called original blades or old blades), and an improvement scheme is proposed based on the old blades to design a new blade to replace the old blades.

[0038] This invention proposes a blade design method. According to the blade design method of this invention, along the spanwise direction of the blade, the entire blade or a certain segment is taken as the design segment. By reducing the design lift coefficient, the blade chord length is increased, the blade twist angle is reduced, or the relative thickness of the blade is decreased, thereby reducing the possibility of blade stall.

[0039] In this method, old blades can be used as reference blades to design new blades, thereby expanding the applicable air density range of the blades and reducing the risk of stall. For example, when the old blades are used in air densities of 1.1 kg / cm³, the new blades can be designed to improve their performance. 3 In situations where stalling occurs, the newly designed blades, through the design method of this invention, can operate at an air density of 1.01 kg / cm³. 3 In this case, stalling will not occur.

[0040] The blade design method according to the present invention may include the following steps:

[0041] The airfoil of each design segment of the blade is determined; multiple design points for that design segment are determined along the blade span; and the design lift coefficients for the multiple design points are set based on a reference lift coefficient. Specifically, the design lift coefficients for the multiple design points can be lower than the reference design lift coefficient by a predetermined value, which can be 0-0.5; curve fitting is performed on the design lift coefficients for the multiple design points to obtain the design lift coefficient curve of the blade.

[0042] When determining the airfoil of each design segment of a new blade, the airfoil of each design segment of the blade can be determined based on a reference blade, which is the blade that stalls at a predetermined position in the spanwise direction under standard design air density ±0.15 kg / m3 conditions, and the predetermined position refers to the standard airfoil position.

[0043] The airfoil of the new blade can be the same as that of the reference blade. For a given airfoil, the maximum lift coefficients CleanCLmax and RoughCLmax are fixed. If wind tunnel testing shows that the new blade can still be designed using the same airfoil as the old blade, then the maximum lift coefficients CleanCLmax and RoughCLmax of the new blade will be the same as those of the old blade.

[0044] When determining the airfoil, either laminar airfoils or high-lift airfoils can be used for blade design. Laminar airfoils have a higher maximum lift-to-drag ratio but a lower maximum lift coefficient; high-lift airfoils, on the other hand, have a very high maximum lift coefficient but a relatively low maximum lift-to-drag ratio. High-lift airfoils are characterized by a natural transition coefficient (Clmax) close to that of fully turbulent flow, which can resist performance degradation caused by leading-edge fouling or surface roughness. When using high-lift airfoils, the design value should not exceed 80% of the upper limit of the aforementioned maximum lift coefficient, RoughCLmax.

[0045] On each design segment, 2 to 15 design points can be identified. For example, the entire blade can be considered as a single design segment, or the blade can be divided into multiple design segments along its span, such as every 2m to 10m, every 5m to 20m, or every 20m to 50m. As an example, the blade can be divided into three design segments, such as the root segment, the mid-segment, and the tip segment. Multiple design points can include at least one location corresponding to 30%, 25%, 24%, 21%, and 18% of the relative thickness. When determining the design points, factors such as blade aerodynamic performance or aerodynamic noise can be considered.

[0046] When setting the design lift coefficients for each design point of the new blade, a reference lift coefficient can be determined first. Optionally, multiple reference lift coefficients for design points can be determined based on a reference blade. For example, the reference lift coefficients can be the design lift coefficients of the reference blade corresponding to the multiple design points. When the length of the new blade increases compared to the reference blade, the maximum lift coefficient of the airfoil corresponding to the extended section, RoughCLmax or CleanCLmax, can be used as the reference lift coefficient.

[0047] For a given airfoil, when multiple design points are standard design points, the reference maximum lift coefficients RoughCLmax or CleanCLmax for these design points can be determined using a lookup table. For other design points, interpolation can be used. The maximum lift coefficient includes the corresponding maximum lift coefficient CleanCLmax for a smooth blade surface and the corresponding maximum lift coefficient RoughCLmax for a rough blade surface. Since the maximum lift coefficient CleanCLmax is higher than the maximum lift coefficient RoughCLmax, and the maximum lift coefficient is fixed for a specific airfoil, for each design point, either the maximum lift coefficient CleanCLmax or RoughCLmax can be used as a reference lift coefficient.

[0048] After determining the reference lift coefficient, the design lift coefficient for that design section is determined based on the reference lift coefficient at the corresponding design point. For example, at the design point corresponding to the reference blade, the design lift coefficient at that point can be set to be 0-0.5 lower than the design lift coefficient of the reference blade.

[0049] The newly designed blade may include a common-mode section with a reference blade and a newly designed section. For example, for a 58-meter-long blade, the inner 40 meters can be common-mode, while the remaining 18 meters are redesigned. In the common-mode section, the design lift coefficient of the multiple design points can be set to be the same as the reference lift coefficient. In the newly designed section, the design lift coefficient of the multiple design points is set to be 0.001 to 0.05 lower than the reference lift coefficient. Preferably, in the newly designed section, the design lift coefficient of the multiple design points is set to be 0.01 to 0.05 lower than the reference lift coefficient. The specific values ​​can be selected based on a relatively safe design lift coefficient set according to the target non-stall air density. The closer to the common-mode section, the smaller the reduction in design lift coefficient relative to the old blade's design lift coefficient.

[0050] To ensure the continuity and smoothness of the design lift coefficient curve between the new design section and the common mode section, 2 to 5 design points need to be selected on the common mode section. These design points are selected within a predetermined length range at the end of the common mode section near the blade tip. For example, if the length of the common mode section is 40m, design points can be selected within the last 2m to 8m of the 40m length, preferably 3 to 4 design points.

[0051] Although the blade design method described above determines the design lift coefficient of the new blade by referring to the design lift coefficient of the old blade, the blade design method of the present invention is not limited to this. It is also possible to determine the design lift coefficient of the new blade by referring to the local Clmax of the new blade, rather than referring to the design lift coefficient of the old blade.

[0052] In addition, the newly designed blade can be longer than the reference blade, that is, it includes an extended section. When determining the design lift coefficient of the extended section, the design lift coefficient of multiple design points on the extended section can be determined based on the maximum lift coefficient RoughCLmax of the airfoil corresponding to the extended section.

[0053] As an example, the design lift coefficient at the blade tip should be 10% lower than the local maximum lift coefficient Clmax (which can be CleanClmax or RoughClmax) by 0-2, especially at the very tip, where the design lift coefficient can be 0. This prevents tip loss and vortex shedding noise caused by the three-dimensional vortex at the blade tip due to the pressure difference between the upper and lower parts of the blade tip. When curve fitting the design lift coefficients at multiple design points on the design section, one of the following methods can be used: (a) each 2m to 10m is considered a design section, and each section is fitted with a function of no more than the fourth power, with a goodness of fit of no less than 0.98; (b) each 10m to 20m is considered a design section, and each section is fitted with a function of no more than the sixth power, with a goodness of fit of no less than 0.97; (c) each 20m to 50m is considered a design section, and each section is fitted with a function of no more than the tenth power, with a goodness of fit of no less than 0.95.

[0054] Figure 1 This is an example diagram comparing the design lift coefficient curve of a new blade with that of an old blade according to an embodiment of the present invention. Figure 1 In the diagram, the horizontal axis represents the blade span, with each grid representing 5 meters of length, and the vertical axis represents the maximum lift coefficient Clmax, with each grid representing 0.2.

[0055] Figure 1 The design lift coefficient curve is obtained by curve fitting the design lift coefficients at multiple design points. These multiple design points represent locations corresponding to multiple relative thickness percentages. For example, in... Figure 1 The example shown illustrates two design points: the first design point could correspond to a position relative to 25% of the thickness, and the second design point could correspond to a position relative to 21% of the thickness.

[0056] In the appendix Figure 1In the diagram, the vertical axis Cl represents the lift coefficient, the horizontal axis represents the spanwise position, New represents the newly designed blade, Old represents the original blade (i.e., the reference blade), the dashed line represents the design lift coefficient curve of the newly designed blade, and the solid line represents the design lift coefficient curve of the reference blade. Taking an example where each square represents 5m of span and 0.2 of vertical dimension, it can be seen that for the reference blade, with a smooth blade surface, the maximum lift coefficient CleanClmax (represented by Old Clean) is approximately 0.2 higher than the maximum lift coefficient RoughClmax (represented by Old Rough) with a rough blade surface. Simultaneously, it can be seen that along the spanwise direction of the blade, the design lift coefficient curve of the newly designed blade is 0-0.18 lower than that of the reference blade. With the increased length of the newly designed blade compared to the reference blade, within the blade tip region, at the second design point shown in the diagram, the design lift coefficient of the new blade is approximately 0.57 lower than the maximum lift coefficient CleanClmax.

[0057] Along the spanwise direction (from the blade root to the blade tip), the relative thickness of the blade airfoil shows a monotonically decreasing trend. Assuming the blade root thickness is set to 100%, as an example, when determining the blade airfoil, the relative thickness in the inner third of the blade (closer to the blade root) can be set to 100%-30%, the relative thickness in the middle third of the blade can be 40%-20%, and the relative thickness in the outer third of the blade (closer to the blade tip) can be 30%-10%.

[0058] When determining the design lift coefficient at each design point, the design lift coefficient of the new blade can be determined by referring to the design lift coefficient of the old blade. Figure 1 Taking the first design point on the left as an example, if the design lift coefficient of the old blade at this point is close to RoughCLmax, then the design lift coefficient of the new blade segment at that corresponding design point can be reduced. For example, if the design lift coefficient of the old blade at this corresponding point is 1.15, then the design lift coefficient of the new blade segment at this point can be set to 1.1. Figure 1Taking the second design point on the right as an example, the corresponding RoughCLmax is approximately 1.4, so the design lift coefficient of the new blade segment at that point can be set to 1.05. In other words, when determining the design lift coefficient of the new blade segment at a design point, it can be set by referring to the design lift coefficient of the old blade at that design point and reducing the design lift coefficient of the new blade segment by 0-0.5. When the new blade is longer than the old blade, within the length range of the extended portion, the design lift coefficient of the new blade segment at that design point can be determined by referring only to the RoughCLmax of the corresponding airfoil at that design point. Therefore, for a blade design segment, the design lift coefficient curve of the blade design segment can be obtained by determining the lift coefficients of at least three design points and then performing curve fitting on the design lift coefficients corresponding to these points.

[0059] Figure 2 This is an example of fitting the lift coefficient curve of a new blade according to an embodiment of the present invention. Figure 2 In the example shown, the reference blade length is 58m, and it is a DU airfoil. This blade stalls when the tip speed ratio is below 9.

[0060] Figure 2 In the diagram, the vertical axis Cl represents the lift coefficient, and the horizontal axis represents the spanwise position, with units of meters (m). For example, each vertical grid represents 0.1 meters, and each spanwise grid represents 5 meters. The upper curve is the design lift curve for the old blade, and the lower curve is the design lift curve for the new blade. The leftmost design point of the two design lift curves can be located in the common-mode section, where the two design lift curves coincide. Along the blade spanwise, the difference between the design lift coefficient of the old blade and the design lift coefficient of the two design points near the common-mode section gradually increases. However, this gradual increase is not always maintained. The difference in design lift coefficient is largest at approximately 16 meters from the first point on the left, and decreases again near the blade tip.

[0061] exist Figure 2 In the example shown, the design lift coefficient curve of the common-mode section is omitted in the spanwise direction of the new blade. The new design section can be divided into three segments (denoted as New2, New3, and New4) for design lift coefficient curve fitting. As an example, these three lift coefficient curves can be quadratic, quartic, and cubic polynomials, respectively, with goodness-of-fit values ​​of 0.9996, 0.9986, and 0.9877. For instance, in the first segment, the newly fitted design lift coefficient curve can be a quadratic function, such as y = -0.0007x. 2+0.0827x-1.273, where y corresponds to the ordinate, representing the lift coefficient, and x represents the spanwise position, in meters (m). In the section corresponding to the design segment, the old blades can be divided into two design segments (Old2 and Old3) for design lift coefficient curve fitting, with goodness-of-fit values ​​of 0.9998 and 0.9995 respectively. In this corresponding design segment, the design lift coefficient curve of the corresponding old blade can also be a quadratic function, expressed as y = 8E-05x 2 +0.0042x+0.6613, goodness of fit R 2 =0.9998. The above expression of the fitted curve and the goodness of fit are merely examples, and the present invention is not limited thereto.

[0062] exist Figure 2 In the example shown, the new blade is longer than the old blade. The design lift coefficient of this increase can be determined by referring to the RoughCLmax of the corresponding airfoil, which will not be described in detail here.

[0063] Figure 3 This is an example comparing the chord lengths of a new blade (denoted as New) and an old blade (denoted as Old) according to an embodiment of the present invention. Figure 3 In the diagram, the vertical axis represents the chord length in meters (m), with each grid representing 0.5m. The horizontal axis represents the spanwise position in meters (m), with each grid representing 5m.

[0064] exist Figure 3 In the example shown, the reference blade is 58m long and stalls when the tip speed ratio is below 9. Therefore, the newly designed blade has a design lift coefficient of 1.1 at the 45m position, which is 0.05 lower than the design lift coefficient of the reference blade at the corresponding position. The relative thickness of the newly designed blade at the 45m design point is 25%. The figure shows that the blade chord length increases as the design lift coefficient decreases.

[0065] Regarding relative thickness, compared to the old blade, at the same spanwise position of the newly designed blade, the relative thickness is 0-15% lower than the original design. In particular, the relative thickness near the blade tip can be even lower, for example, 20%. Furthermore, maintaining a locally constant relative thickness or monotonically decreasing from the blade root to the blade tip can improve the overall aerodynamic performance of the blade by about 0-5%, reduce aerodynamic noise by 0-5 dBA, and also improve the noise reduction of aerodynamic accessories by 0-3 dBA.

[0066] Figure 4 This is an example comparing the twist angles of a new blade and an old blade according to an embodiment of the present invention. The vertical axis represents the twist angle in degrees (deg), and the horizontal axis represents the spanwise position. Each vertical division represents 1 degree, and each horizontal division represents 5 meters. The figure shows that the twist angle of the newly designed blade is much smaller in absolute value than that of the reference blade.

[0067] exist Figure 4 In the example shown, the reference blade is 58m long and stalls at tip speeds below 9. Therefore, the newly designed blade at 45m has a design lift coefficient of 1.1, which is 0.05 lower than the design lift coefficient of the reference blade at the corresponding position. The relative thickness of the new blade at the 45m design point is 25%.

[0068] Figure 5 This is an example graph showing the lift coefficient curves of a novel blade according to an embodiment of the present invention under different incoming wind velocities. The horizontal axis represents the spanwise position in meters (m), with each cell representing 5 meters. The vertical axis represents the lift coefficient Cl, with each cell representing 0.2.

[0069] pass Figure 5 It can be seen that when the blades reach the transition zone, with the rotational speed remaining constant and the wind speed increasing, the angle of attack and lift coefficient increase, and the newly designed blades are further from CleanClmax. If the blade manufacturing process is poor or there is a lot of wind, sand, or mosquitoes at the project site, the new design will also be further from RoughClmax, and the blades will find it difficult to enter a stall state. If the blades do not enter a stall state, the power generation performance is good, the AEP (Annual Power Output) is high, the noise is low, all components of the whole machine are stable, and the safety is high.

[0070] According to the blade design method of the present invention, by designing a blade profile with a large chord length, small twist angle, and low relative thickness, the possibility of blade stall is reduced, and the aerodynamic performance of the blade is improved while reducing blade aerodynamic noise. According to the design method of the present invention, by reducing the design lift coefficient of the blade, the blade chord length is increased. As an example, for an original blade with a length of 60m, the chord length of the newly designed blade can be approximately 0% to 500% longer than that of the original blade (approximately 0 to 1.5m), the twist angle can be approximately 0 to 10 degrees smaller than the original design, the design lift coefficient can be 0 to 0.5 lower than the original design, and the relative thickness can be 0 to 200% lower than the original design (approximately 0 to 20% of the absolute value of the relative thickness).

[0071] The advantage of the blade design method of the present invention is that the new blade can operate at a lower angle of attack or lift coefficient, with a margin of 0-5 degrees or 0-0.5 degrees from the stall angle of attack or lift coefficient, even if there are certain deviations in blade manufacturing or the leading edge is not smooth enough, or the air density is low, such as 1.0 kg / m³. 3 Even if the unit is not properly controlled or the wind speed changes suddenly, it will not cause stall. Compared with the new design, the old design has a smaller chord length, lower solidity, and a higher lift coefficient, making it particularly prone to local stall or large-area stall, which will cause a drop in the power curve, increase noise, and in severe cases, may lead to blade vibration.

[0072] According to one aspect of the present invention, a blade for a wind turbine generator is provided, the blade having an airfoil of DU, and the blade can be designed using the blade design method described above.

[0073] For a blade span of 0m to the tip, the design lift coefficient ranges from 0 to 3, the blade chord length ranges from 0 to 5m, the twist angle ranges from -10 to 2 degrees, and the relative thickness ranges from 10% to 100%. As an example, when the blade length is between 58m and 65m, at a span of 40m to 50m, the design lift coefficient can be between 1.0 and 1.2, the blade chord length can be between 1.3m and 1.4m, the blade twist angle can be between -2 and 0 degrees, and the relative thickness can be between 20% and 30%.

[0074] The features, structures, or characteristics described in this invention can be combined in any suitable manner in one or more embodiments. In the above description, numerous specific details are provided to give a full understanding of embodiments of the invention. However, those skilled in the art will recognize that the technical solutions of the invention can be practiced without one or more of the specific details described, or other methods, components, materials, etc., can be employed. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring various aspects of the invention.

Claims

1. A blade design method, characterized in that, The blade design method includes the following steps: Along the spanwise direction of the blade, the entire blade or a section thereof is taken as the design segment; Along the blade span, determine multiple design points for the design segment; Set the design lift coefficient for the plurality of design points such that the design lift coefficient for the plurality of design points is lower than the reference design lift coefficient by a predetermined value; The design lift coefficient of the blade is obtained by curve fitting the design lift coefficient of the multiple design points. Based on the designed lift coefficient curve, increasing the blade chord length, decreasing the blade twist angle, or reducing the relative thickness of the blade can reduce the possibility of blade stall.

2. The blade design method according to claim 1, characterized in that, The blade design method further includes the following steps: determining the airfoil of the design segment before determining multiple design points of the design segment.

3. The blade design method according to claim 2, characterized in that, determining a blade airfoil for each design section of the blade based on a reference blade, the reference blade being a blade at a predetermined position in the spanwise direction at a standard design air density ± 0.15 kg / m 3 under which the blade stalls, the predetermined position being a standard airfoil position.

4. The blade design method according to claim 3, characterized in that, The reference design lift coefficient refers to the design lift coefficient corresponding to the reference blade at the plurality of design points, and the design lift coefficient at the plurality of design points is 0 to 0.5 lower than the reference design lift coefficient.

5. The blade design method according to claim 4, characterized in that, The blade includes a common-mode section that shares the same design mode as the reference blade and a new design section. In the common-mode section, the design lift coefficient of the plurality of design points is set to be the same as the reference design lift coefficient. In the new design section, the design lift coefficient of the plurality of design points is set to be 0.001 to 0.5 lower than the reference design lift coefficient.

6. The blade design method according to claim 5, characterized in that, In the new design section, the design lift coefficient of the plurality of design points is set to be 0.01 to 0.05 lower than the reference design lift coefficient.

7. The blade design method according to claim 1, characterized in that, The reference design lift coefficient includes the maximum lift coefficient corresponding to the airfoil.

8. The blade design method according to claim 2, characterized in that, When the blade is divided into multiple design segments along the spanwise direction, curve fitting is performed using one of the following methods: (a) Each 2m to 10m is a design segment, and each segment is fitted with a function of no more than the fourth power, with a goodness of fit of no less than 0.98; (b) Each 10m to 20m section is a design segment, and each segment is fitted with a function of power no more than 6, with a goodness of fit of no less than 0.97; (c) Each 20m to 50m segment is a design segment. Each segment is fitted with a function of power no more than 10, and the goodness of fit is no less than 0.

95.

9. The blade design method according to claim 2, characterized in that, The blade airfoil is either a laminar flow airfoil or a high-lift airfoil.

10. The blade design method according to claim 2, characterized in that, The plurality of design points include at least one of the locations corresponding to relative thicknesses of 30%, 25%, 24%, 21%, and 18%.

11. The blade design method according to claim 5, characterized in that, The blade is longer than the reference blade and includes an extended section. The design lift coefficient of multiple design points on the extended section is determined based on the maximum lift coefficient CLmax of the airfoil corresponding to the extended section.

12. The blade design method according to claim 5, characterized in that, Select at least two design points within a 2m-8m area near the blade tip in the common mode section.

13. The blade design method according to claim 11, characterized in that, The design lift coefficient of the 10% section at the tip of the blade is 0-2 lower than the local maximum lift coefficient CLmax, and the design lift coefficient at the tip is 0.

14. A blade for a wind turbine generator set, characterized in that, The blade is designed according to the blade design method according to any one of claims 1-13, and the airfoil of the blade is a DU series airfoil.

15. The blade for a wind turbine generator according to claim 14, characterized in that, At a blade span of 40m to 50m, the design lift coefficient of the blade is 1.0 to 1.

2.

16. The blade for a wind turbine generator according to claim 15, characterized in that, The blade chord length is 1.3m to 1.4m.

17. The blade for a wind turbine generator according to claim 15, characterized in that, The twist angle of the blade is -2 to 0 degrees.

18. The blade for a wind turbine generator according to claim 15, characterized in that, The relative thickness of the blade is 20% to 30%.

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