Method for controlling section stiffness of aeroelastic scaling model of wind power blade

Abstract

The invention discloses a method for controlling the section stiffness of an aeroelastic scaling model of a wind power blade, and belongs to the technical field of wind tunnel flutter tests. According to the method, a scale model of the wind power blade adopts a single-beam structure, sectional foam is used as internal filling, meanwhile, glass fibers are used as manufacturing materials of a skin and a beam, and due to the fact that the wind power blade is of a structure with a large slenderness ratio, low-order vibration mode multi-position waving and shimmy are achieved, and the wind power blade has a large slenderness ratio. The rigidity control mainly ensures the rigidity in the waving direction and the swinging direction. In the spanwise direction of the blade, the blade is cut into a plurality of sections, so that the blade section between the two sections is linearly approximate; meanwhile, the section obtained by segmenting the blade is an airfoil section, the airfoil section is segmented into a front section, a middle section and a rear section in the chordwise direction of the blade airfoil section, then the section rigidity of the scaling model can be controlled by controlling the thickness of the skin and the thickness of the beam of each part according to the required rigidity, and then the elastic similarity of the model can be achieved.

Description

Technical Field

[0001] The invention relates to a method for controlling the cross-section stiffness of an aeroelastic scaled model of a wind turbine blade, and belongs to the technical field of wind tunnel flutter tests. Background Art

[0002] Flutter research is an indispensable part of the design process of large wind turbine blades today, and wind tunnel flutter tests are an important part of flutter research. Since flutter has many forms, the mathematical and physical relationships that need to be considered when calculating the critical flutter speed are very complex. Therefore, in the design process of large wind turbine blades, the wind tunnel flutter test can be used to verify whether the wind turbine blades will flutter. The wind tunnel flutter test requires a blade scale with similar aeroelasticity, and the stiffness control design of the model is a key point. At present, the model design and production methods for aeroelastic wind tunnel tests can be divided into three methods: single degree of freedom, multi-degree of freedom, and continuous aeroelastic. The existing production methods of aeroelastic models of different structures are quite different, and there are few stiffness control schemes for existing scaled models. People are eager to find a simple, reliable, and efficient design scheme for the cross-sectional stiffness control of wind turbine blade wind tunnel flutter models. Summary of the invention

[0003] In view of the shortcomings of the existing wind tunnel flutter model design technology for wind turbine blades, the present invention provides a method for controlling the cross-sectional stiffness of an aeroelastic scaled model of a wind turbine blade. When designing the wind tunnel flutter model of the blade, it is used in conjunction with the open source software Precomp to simply and efficiently design the scaled model.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: a method for controlling the cross-sectional stiffness of an aeroelastic scaled model of a wind turbine blade, comprising the following steps:

[0005] S1. The blade model is filled with a single beam and segmented foam. The single beam is placed at the original blade web position. The foam filled at the leading and trailing edges plays a dimensional role. The thickness of the foam is greater than 10 mm. The stiffness of the blade is provided by the skin and the single beam. The section stiffness of the blade is controlled by setting the thickness parameters of the two.

[0006] S2. The proportional coefficient formula of the reduction ratio is obtained by deriving the reduction ratio theory:

[0007] Frequency ratio , stiffness ratio ;

[0008] in: scale ratio; Speed ​​ratio; ; Material density ratio; Air density ratio;

[0009] Then, based on the existing original section stiffness and mass information (the original model parameters input by the project), the proportional coefficient is used to calculate the target value data of the section stiffness and frequency in the swing and shimmy directions of the scaled model;

[0010] S3. According to the obtained cross-sectional stiffness data in the flapping direction, the blade is divided into multiple segments along the span direction by selecting a splitting plane, each segment adopts the same thickness parameter setting, that is, the stiffness change of each segment is approximately linear; the position of the splitting plane is selected to ensure that the cross-sectional stiffness design value in the flapping direction after segmentation is within the error of the cross-sectional stiffness target value obtained by scaling;

[0011] S4. After the segmentation surface is selected, the selected segmentation section is segmented along the chord direction of the airfoil, and the segmentation positions are 0.2~0.3 and 0.7~0.8 of the chord line respectively, and the airfoil is divided into three sections: front, middle and rear. That is, after being segmented into multiple sections along the span direction, each section is further divided into three parts: front, middle and rear. The front and rear sections control the stiffness in the swing direction, and the middle section controls the stiffness in the flapping direction.

[0012] S5. Then use Precomp software, according to the above segmentation design method, input data to calculate the section stiffness, and cooperate with the optimization software to obtain the skin thickness of each segmented part and the thickness parameters of the single beam;

[0013] S6. Based on the obtained thickness parameters, finite element software is used to perform modeling and calculate the structural dynamic characteristics of the model;

[0014] S7. Since the stiffness of the blade root and blade tip is very extreme, the blade root and blade tip are ignored in the Precomp calculation in step S5. The thickness parameters of the skin at the blade root and blade tip are manually fine-tuned to obtain the required final modal parameters, and finally the model making parameters are derived from the finite element.

[0015] Furthermore, the error of the cross-sectional stiffness target value is 10%.

[0016] Furthermore, the skin and single beam of the model are made of glass fiber material.

[0017] The beneficial effects of the present invention are as follows: the scaled model of the wind turbine blade adopts a single beam structure, with segmented foam as internal filling, and glass fiber is used as the material for the skin and beam. Because the wind turbine blade is a structure with a large aspect ratio, the low-order vibration mode has multiple swings and shimmies, so the control of stiffness mainly ensures the stiffness in the swinging direction and the swinging direction. Along the span direction of the blade, by cutting the blade into multiple sections, the blade segments between the two sections are linearized and approximated; at the same time, the section divided from the blade, i.e., the airfoil, is divided into three sections in the chord direction of the blade airfoil - front, middle, and rear. At this time, according to the required stiffness, the section stiffness of the scaled model can be controlled by controlling the thickness of the skin and the thickness of the beam of each part, and then the elastic similarity of the model can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 It is a partial stereogram of the present invention.

[0020] Figure 3 It is a comparison chart of section stiffness results.

[0021] In the figure: 1. leading edge of the skin, 2. middle section of the skin, 3. trailing edge of the skin, 4. single beam, 5. foam. DETAILED DESCRIPTION

[0022] The present invention is described below with reference to the accompanying drawings and specific embodiments:

[0023] Figure 1 and Figure 2 The overall structure diagram of the present invention is shown, in which a scaled-down aeroelastic model of a wind turbine blade can be seen, which is divided into three sections, namely the leading edge 1 of the skin, the middle section 2 of the skin and the trailing edge 3 of the skin; the interior of the model is supported by a single beam 4 and the two sides are filled with foam 5.

[0024] A method for controlling the cross-sectional stiffness of an aeroelastic scaled model of a wind turbine blade comprises the following steps:

[0025] Step 1: First, the interior of the blade model is designed to be filled with a single beam and segmented foam. The beam can be placed according to the position of the original blade web. The foam filled at the leading and trailing edges plays a dimensional role. The thickness is generally set to be greater than 10mm. This structural design makes the blade stiffness mainly provided by the skin and single beam. The section stiffness of the blade is controlled by setting its thickness parameters. The skin and beam of the model are made of fiberglass material, and the interior of the model adopts a single beam and foam filling design.

[0026] Step 2: Then, the scaling coefficient formula is obtained by deriving the scaling theory:

[0027] Frequency ratio: , stiffness ratio: ;

[0028] in: scale ratio; Speed ​​ratio; ; Material density ratio; Air density ratio;

[0029] Then, based on the existing original section stiffness and mass information (the original model parameters input by the project), the proportional coefficient is calculated to obtain the target information such as the section stiffness (flapping and shimmying directions) and frequency of the scaled model.

[0030] Step 3: According to the obtained section stiffness data in the flapping direction, select the splitting surface along the span direction of the blade and split it into multiple segments. Each segment uses the same thickness parameter setting, that is, the stiffness change of each segment is approximately linear. The position of the splitting surface selection should ensure that the section stiffness data in the flapping direction after segmentation is within the error (10%). The model is designed in sections along the span direction, and the material thickness of each segment is the same, so that the stiffness change of each segment is linear.

[0031] Step 4: After the segmentation surface is selected, the selected segmentation section is segmented along the chord direction of the airfoil. The segmentation positions are 0.2~0.3 and 0.7~0.8 of the chord line respectively, and the airfoil is divided into the front, middle and rear sections. After being segmented into multiple sections along the span direction, each section is further divided into the front, middle and rear parts (the front and rear sections mainly control the swing stiffness, and the middle section mainly controls the flapping direction stiffness);

[0032] Step 5: Then use the Precomp software, according to the above-mentioned segmentation design method, input data to calculate the section stiffness, and cooperate with the optimization software to quickly obtain the skin thickness and beam thickness parameters of each segmented part.

[0033] Step 6: Based on the obtained thickness, finite element software can be used to build a model and calculate the structural dynamic characteristics of the model.

[0034] Step 7: Since the stiffness at the root and tip of the blade is very extreme, it can be ignored in the Precomp calculation. The thickness parameters of the skin at the root and tip are manually fine-tuned to obtain the required final modal parameters, and finally the model manufacturing parameters are derived from the finite element.

[0035] Figure 3This is a comparison chart of the section stiffness results. It can be seen from the figure that according to the above skin partitioning method, after the thickness is optimized, the result is very close to the target value (the error is less than 10%). This solution solves the problem of similar aerodynamic elasticity of the model when making a scaled flutter model with similar aerodynamic elasticity for large wind turbine blades. This design method does not require additional new processes and new materials, which facilitates the design, production and inspection of the model.

[0036] The scheme of the present invention is simple, reliable and efficient. In the design process of the wind turbine blade scaled model, the cross-sectional stiffness of the blade scaled model can be quickly controlled to complete the design of the aeroelastic similarity of the model. The skin and beam designed by this method can be conveniently manufactured in the production of the skin and beam after the design parameters are obtained, without the need for additional steps, and the cross-sectional stiffness of the obtained model has good accuracy.

[0037] Final note: The above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution of the embodiments of the present invention.

Claims

1. A method for controlling the cross-sectional stiffness of a wind turbine blade aeroelastic scaled model, characterized in that: The following steps are involved: S1. The blade model is filled with a single beam and segmented foam. The single beam is placed at the original blade web position. The foam filled at the leading and trailing edges plays a dimensional role. The thickness of the foam is greater than 10 mm. The stiffness of the blade is provided by the skin and the single beam. The section stiffness of the blade is controlled by setting the thickness parameters of the two. S2. The proportional coefficient formula of the reduction ratio is obtained by deriving the reduction ratio theory: Frequency ratio , stiffness ratio ; in: Scale ratio, Speed ​​ratio, ; Material density ratio; Air density ratio; Then, based on the existing original section stiffness and mass information, the target value data of the section stiffness and frequency in the swing and shimmy directions of the scaled model are calculated using the proportional coefficient; S3. According to the obtained cross-sectional stiffness data in the flapping direction, the blade is divided into multiple segments along the span direction by selecting a splitting plane, each segment adopts the same thickness parameter setting, that is, the stiffness change of each segment is approximately linear; the position of the splitting plane is selected to ensure that the cross-sectional stiffness design value in the flapping direction after segmentation is within the error of the cross-sectional stiffness target value obtained by scaling; S4. After the segmentation surface is selected, the selected segmentation section is segmented along the chord direction of the airfoil, and the segmentation positions are 0.2~0.3 and 0.7~0.8 of the chord line respectively, and the airfoil is divided into three sections: front, middle and rear. That is, after being segmented into multiple sections along the span direction, each section is further divided into three parts: front, middle and rear. The front and rear sections control the stiffness in the swing direction, and the middle section controls the stiffness in the flapping direction. S5. Then use Precomp software, according to the above segmentation design method, input data to calculate the section stiffness, and cooperate with the optimization software to obtain the skin thickness of each segmented part and the thickness parameters of the single beam; S6. Based on the obtained thickness parameters, finite element software is used to perform modeling and calculate the structural dynamic characteristics of the model; S7. Since the stiffness of the blade root and blade tip is very extreme, the blade root and blade tip are ignored in the Precomp calculation in step S5. The thickness parameters of the skin at the blade root and blade tip are manually adjusted to obtain the required final modal parameters, and finally the model manufacturing parameters are derived from the finite element.

2. The method for controlling the cross-sectional stiffness of a wind turbine blade aeroelastic scaled model according to claim 1, characterized in that: The error of the cross-sectional stiffness target value is 10%.

3. The method for controlling the cross-sectional stiffness of a wind turbine blade aeroelastic scaled model according to claim 1, characterized in that: The skin and single beam of the model are made of fiberglass material.

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