A method for modifying aerodynamic loads of wind turbine blades in shutdown condition considering geometric effects
By constructing a method for correcting aerodynamic loads on wind turbine blades under shutdown conditions that takes into account geometric effects, the problem of the failure to effectively consider geometric effects in the existing technology is solved, and accurate load prediction of wind turbine blades under shutdown conditions is achieved, thus improving the accuracy of three-dimensional aerodynamic correction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2026-05-06
- Publication Date
- 2026-06-02
AI Technical Summary
Existing three-dimensional effect correction models fail to effectively consider geometric effects under the shutdown condition of wind turbine blades, resulting in inaccurate load predictions, especially lacking an effective theoretical model under non-rotating conditions.
By constructing a method for correcting aerodynamic loads on wind turbine blades under shutdown conditions that takes into account geometric effects, including calculating geometric axial and radial induction factors, and combining the incoming flow velocity and angle of attack, the lift and drag coefficients of the three-dimensional blade are corrected to establish an accurate aerodynamic model.
It enables accurate load prediction of wind turbine blades under shutdown conditions, improving the accuracy of three-dimensional aerodynamic correction, especially in the description of downwash and tip loss effects, with prediction accuracy improved by more than 50%.
Smart Images
Figure CN122133568A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of aerodynamic prediction technology for wind turbine blades, and specifically to a method for correcting aerodynamic loads on wind turbine blades under shutdown conditions that takes into account geometric effects. Background Technology
[0002] Currently, horizontal axis wind turbines are developing towards larger scale and greater production capacity. However, due to the complex inflow conditions and diverse operating modes faced by horizontal axis wind turbines, accurate assessment of blade aerodynamics is crucial to ensuring both power generation and turbine operational safety.
[0003] Currently, wind turbine industrial design departments widely use engineering prediction methods based on momentum blade element theory. However, the two-dimensional assumptions of blade element theory lead to a significant discrepancy between the aerodynamic loads it describes and the actual three-dimensional loads on the blade. Classical three-dimensional effect correction models simulate the blade rotation enhancement phenomenon, i.e., the three-dimensional effects caused by blade rotation, through complex mathematical expressions. However, the three-dimensional aerodynamic forces induced by the blade's own three-dimensional geometry under non-rotating conditions are often neglected; for example, there is a lack of effective theoretical models for changes in the equivalent angle of attack induced by downwash. Therefore, it is necessary to develop aerodynamic models for three-dimensional geometric effects to compensate for the deficiencies in existing three-dimensional effect correction models, achieve accurate prediction of blade loads under shutdown conditions, and ultimately improve the accuracy of three-dimensional aerodynamic correction for blades. Summary of the Invention
[0004] In view of the above-mentioned shortcomings in the prior art, the present invention provides a method for correcting aerodynamic loads of wind turbine blades under shutdown conditions that considers geometric effects. This method solves the defects in the existing three-dimensional effect correction model, realizes accurate prediction of blade loads under shutdown conditions, and ultimately improves the accuracy of three-dimensional aerodynamic correction of blades.
[0005] To achieve the aforementioned objectives, the present invention employs the following technical solution: a method for correcting aerodynamic loads on wind turbine blades under shutdown conditions, considering geometric effects, comprising the following steps: S1: Obtain load data for each two-dimensional section of the three-dimensional blade of the wind turbine, including lift and drag data corresponding to the airfoil angle of attack; S2: By plotting and analyzing two-dimensional load data, determine the zero-lift angle of attack corresponding to a lift coefficient of 0, and define a two-dimensional equivalent angle of attack based on the zero-lift angle of attack; S3: For the three-dimensional blade and the cross-section under the target occupancy, calculate the position ratio of the target occupancy on the blade and the local aspect ratio; S4: Based on the two-dimensional equivalent angle of attack, the position ratio of the target occupancy and the local aspect ratio, calculate the geometric axial induction factor, and combine it with the incoming flow velocity to calculate the corresponding axial induction velocity; S5: Calculate the equivalent angle of attack of the blade at this section based on the axial velocity decay caused by the axial induced velocity; S6: Based on the equivalent angle of attack of the cross section, calculate the geometric radial induction factor and obtain the corresponding radial induced velocity by combining the incoming flow velocity; S7: Calculate the three-dimensional lift of the blade section at the angle of attack based on the radial induced velocity and the equivalent angle of attack; S8: Based on three-dimensional lift, two-dimensional equivalent angle of attack and equivalent angle of attack, calculate the induced drag induced by downwash, and obtain the drag coefficient of the three-dimensional blade section considering the equivalent angle of attack correction and induced drag correction, so as to realize the aerodynamic load correction of wind turbine blades under shutdown conditions considering geometric effects.
[0006] Furthermore, the two-dimensional equivalent angle of attack The calculation formula is: in, For airfoil angle of attack, It is zero-lift angle of attack.
[0007] Furthermore, the geometric axis induction factor The calculation formula is: in, and These are empirical parameters. The target occupancy distance is the distance from the leaf root. For the blade length, Let be the chord length of each position; The axial induced velocity The calculation formula is: in, The incoming flow velocity.
[0008] Furthermore, the equivalent angle of attack The calculation formula is: .
[0009] Furthermore, the geometric radial induction factor The calculation formula is: in, These are empirical parameters; The radial induced velocity The calculation formula is: .
[0010] Furthermore, the three-dimensional lift The calculation formula is: in, For equivalent angle of attack The corresponding lift.
[0011] Furthermore, the induced resistance The calculation formula is: Drag coefficient of three-dimensional blade section considering equivalent angle of attack correction and induced drag correction for: in, For equivalent angle of attack The corresponding resistance.
[0012] The beneficial effects of this invention are: (1) This invention constructs a three-dimensional aerodynamic correction model for blades that considers geometric effects. Traditional correction models only consider the three-dimensional aerodynamics caused by rotational effects through data fitting, neglecting geometric effects. In addition, this theoretical model has the potential to be extended to different aircraft types and different flow states. This technology makes up for the deficiencies in related technical fields. (2) Based on Bernoulli's law and the physical laws of three-dimensional downwash flow, this invention constructs a geometric effect correction to achieve accurate prediction of loads under shutdown conditions, including a description model of downwash flow and a description model of tip loss. Classical engineering methods only use two-dimensional airfoil data to calculate loads under shutdown conditions, while this invention achieves a significant improvement in the accuracy of load prediction under non-rotating shutdown conditions. Attached Figure Description
[0013] Figure 1 The flowchart illustrates the aerodynamic load correction method for wind turbine blades under shutdown conditions that takes into account geometric effects, as described in this invention.
[0014] Figure 2 A comparison chart of the lift line prediction results at 25% of the stations and the original method.
[0015] Figure 3 A comparison chart of the predicted lift line at 35% of the stations and the original method.
[0016] Figure 4 A comparison chart showing the predicted lift line at 65% of the stations with the original method.
[0017] Figure 5 A comparison chart showing the predicted lift lines at 82% of the stations with the original method.
[0018] Figure 6This is a comparison chart of the predicted resistance line at the 25% station position and the original method.
[0019] Figure 7 A comparison chart showing the predicted resistance line at the 35% station position with the original method.
[0020] Figure 8 This is a comparison chart of the predicted resistance line at the 65% station position and the original method.
[0021] Figure 9 This is a comparison chart of the predicted resistance line at 82% of the station position with the original method. Detailed Implementation
[0022] This invention addresses the gap in engineering models for wind turbines by establishing a correction for the equivalent angle of attack based on the three-dimensional underwash flow theory in aerospace engineering, thus achieving accurate prediction of the lift line slope. Furthermore, it considers flow leakage induced by blade tip shape, further assisting those skilled in the art in understanding and using this invention. The invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0023] like Figure 1 As shown, a method for correcting aerodynamic loads on wind turbine blades under shutdown conditions, considering geometric effects, includes the following steps: S1: Obtain load data for each two-dimensional section of the three-dimensional blade of the wind turbine, including lift and drag data corresponding to the airfoil angle of attack; In this embodiment, MEXICO wind turbine standard data is used as a typical example. Since the wind turbine consists of three airfoils, including DU 91-W2-25, RISØ A1-21, and NACA 64418, lift and drag coefficients for these three airfoils are prepared, including different airfoil angles of attack. The corresponding lift ,resistance data; S2: By plotting and analyzing two-dimensional load data, determine the zero-lift angle of attack corresponding to a lift coefficient of 0, and define a two-dimensional equivalent angle of attack based on the zero-lift angle of attack; The two-dimensional equivalent angle of attack The calculation formula is: in, For airfoil angle of attack, It is zero-lift angle of attack.
[0024] S3: For the three-dimensional blade and the cross-section under the target occupancy, calculate the position ratio of the target occupancy on the blade and the local aspect ratio; This embodiment focuses on the three-dimensional blade and the cross-section under the target location to determine the incoming flow velocity. blade length Target occupancy distance from leaf root chord length of each position This allows for the calculation of the target's position relative to the entire blade. Local aspect ratio ; In this embodiment, for The four sections are 25%, 35%, 60%, and 82%. =0.223, 0.20, 0.142, 0.115; In this step, the method for determining the angle of attack of the incoming flow at each cross-section is as follows: When the wind turbine is stopped, the angle of attack of the incoming flow on the blade section is determined by the blade pitch angle. and the twist angle of the blade section Combined influence. The angle of attack of the incoming flow at this time... For the same blade, the different angles of attack at different cross-sections are solely due to their different torsion angles.
[0025] S4: Based on the two-dimensional equivalent angle of attack, the position ratio of the target occupancy and the local aspect ratio, calculate the geometric axial induction factor, and combine it with the incoming flow velocity to calculate the corresponding axial induction velocity; The geometric axial induction factor The calculation formula is: in, and These are empirical parameters. The target occupancy distance is the distance from the leaf root. For the blade length, Let be the chord length of each position; This characterizes the position of the cross section from the blade tip. It represents the ratio of local leaf element chord length to leaf length.
[0026] This formula demonstrates that the more the airfoil is positioned closer to the blade root and the greater the local aspect ratio, the more significant the downwash effect will be.
[0027] The axial induced velocity The calculation formula is: in, The incoming flow velocity.
[0028] S5: Calculate the equivalent angle of attack of the blade at this section based on the axial velocity decay caused by the axial induced velocity; The equivalent angle of attack The calculation formula is: This formula characterizes the change in angle of attack caused by the axial velocity loss induced by the downwash flow.
[0029] S6: Based on the equivalent angle of attack of the cross section, calculate the geometric radial induction factor and obtain the corresponding radial induced velocity by combining the incoming flow velocity; The geometric radial induction factor The calculation formula is: in, These are empirical parameters. The distribution of radial induced velocity was characterized along the entire leaf blade, with the radial velocity increasing closer to the leaf tip, reflecting significant tip loss.
[0030] The radial induced velocity The calculation formula is: S7: Calculate the three-dimensional lift of the blade section at the angle of attack based on the radial induced velocity and the equivalent angle of attack; The three-dimensional lift The calculation formula is: in, For equivalent angle of attack The corresponding lift.
[0031] This formula determines the incoming flow velocity. Angle of attack of the cross section The lift coefficient of the blade section at that time. Its lift coefficient includes the lift coefficient interpolated from the two-dimensional airfoil database after the equivalent angle of attack correction, and also includes a portion of the load variation caused by the tip loss effect.
[0032] Method for determining the lift coefficient obtained by interpolation from the two-dimensional airfoil database after equivalent angle of attack correction: For the blade lift coefficient in the embodiment, after determining the incoming flow angle of attack and its corresponding equivalent angle of attack, the three-dimensional lift coefficient of the blade section is the lift coefficient in the two-dimensional airfoil database corresponding to the equivalent angle of attack under this flow state.
[0033] S8: Based on three-dimensional lift, two-dimensional equivalent angle of attack and equivalent angle of attack, calculate the induced drag induced by downwash, and obtain the drag coefficient of the three-dimensional blade section considering the equivalent angle of attack correction and induced drag correction, so as to realize the aerodynamic load correction of wind turbine blade shutdown condition considering geometric effects. The induced resistance The calculation formula is: This formula shows that induced drag is due to the coupling effect of the induced angle of attack and lift generated by downwash, i.e., lift-induced drag.
[0034] Drag coefficient of three-dimensional blade section considering equivalent angle of attack correction and induced drag correction for: in, For equivalent angle of attack The corresponding resistance.
[0035] Its drag coefficient includes the drag coefficient obtained by interpolation from the two-dimensional airfoil database after the equivalent angle of attack correction, and also includes a portion of the load variation caused by the tip loss effect.
[0036] Method for determining the drag coefficient obtained by interpolation from the two-dimensional airfoil database after equivalent angle of attack correction: For the blade drag coefficient in the embodiment, after determining the incoming flow angle of attack and its corresponding equivalent angle of attack, the three-dimensional drag coefficient of the blade section is the drag coefficient in the two-dimensional airfoil database corresponding to the equivalent angle of attack under this flow state.
[0037] This formula determines the incoming flow velocity. Angle of attack of the cross section The blade section drag coefficient at that time.
[0038] In one embodiment of the present invention, the MEXICO wind turbine rotor (Measurements and Experiments In Controlled Conditions) is a classic standard example in the field of wind turbines. The MEXICO wind turbine rotor comprises three wind turbine blades, each 2.25m in length. Each blade of the MEXICO wind turbine is composed of three different airfoils: the root airfoil is DU 91-W2-250, the middle airfoil is RISØ A1-21, and the tip airfoil is NACA 64418.
[0039] Specifically, Figures 2-5 The paper demonstrates the predictive performance of the geometric effect correction model for lift coefficients at different spanwise cross-sections. It can be seen that the proposed geometric effect correction model (solid black line) matches the high-precision experimental data (black box) well. In blade element theory, blade loads under shutdown conditions are often predicted using two-dimensional aerodynamic data. Therefore, the original prediction results shown in the figure (dashed line) exhibit significant errors compared to the experimental data. The prediction accuracy is improved by more than 50%. Figures 6-9 The results demonstrate the prediction of drag across a three-dimensional blade cross section, showing that the proposed geometric effect correction model can more accurately predict drag across the three-dimensional blade cross section.
[0040] In summary, this invention proposes a corrected model for three-dimensional geometric effects, achieving accurate prediction of the downwash effect and tip loss effect induced by three-dimensional geometry. The results of the implementation examples show that the theoretical model developed in this paper can achieve high prediction accuracy for lift and drag at different cross-sectional positions and for different airfoils. Compared with the classical blade element theory, the accuracy of the model proposed in this invention is improved by more than 50%, further enhancing the industry's ability to predict three-dimensional blade aerodynamics.
[0041] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the invention.
Claims
1. A method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects, characterized in that, Includes the following steps: S1: Obtain load data for each two-dimensional section of the three-dimensional blade of the wind turbine, including lift and drag data corresponding to the airfoil angle of attack; S2: By plotting and analyzing two-dimensional load data, determine the zero-lift angle of attack corresponding to a lift coefficient of 0, and define a two-dimensional equivalent angle of attack based on the zero-lift angle of attack; S3: For the three-dimensional blade and the cross-section under the target occupancy, calculate the position ratio of the target occupancy on the blade and the local aspect ratio; S4: Based on the two-dimensional equivalent angle of attack, the position ratio of the target occupancy and the local aspect ratio, calculate the geometric axial induction factor, and combine it with the incoming flow velocity to calculate the corresponding axial induction velocity; S5: Calculate the equivalent angle of attack of the blade at this section based on the axial velocity decay caused by the axial induced velocity; S6: Based on the equivalent angle of attack of the cross section, calculate the geometric radial induction factor and obtain the corresponding radial induced velocity by combining the incoming flow velocity; S7: Calculate the three-dimensional lift of the blade section at the angle of attack based on the radial induced velocity and the equivalent angle of attack; S8: Based on three-dimensional lift, two-dimensional equivalent angle of attack and equivalent angle of attack, calculate the induced drag induced by downwash, and obtain the drag coefficient of the three-dimensional blade section considering the equivalent angle of attack correction and induced drag correction, so as to realize the aerodynamic load correction of wind turbine blades under shutdown conditions considering geometric effects.
2. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 1, characterized in that, The two-dimensional equivalent angle of attack The calculation formula is: in, For airfoil angle of attack, It is zero-lift angle of attack.
3. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 2, characterized in that, The geometric axial induction factor The calculation formula is: in, and These are empirical parameters. The target occupancy distance is the distance from the leaf root. For the blade length, Let be the chord length of each position; The axial induced velocity The calculation formula is: in, The incoming flow velocity.
4. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 3, characterized in that, The equivalent angle of attack The calculation formula is: 。 5. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 4, characterized in that, The geometric radial induction factor The calculation formula is: in, These are empirical parameters; The radial induced velocity The calculation formula is: 。 6. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 5, characterized in that, The three-dimensional lift The calculation formula is: in, For equivalent angle of attack The corresponding lift.
7. The method for correcting aerodynamic loads on wind turbine blades under shutdown conditions considering geometric effects according to claim 6, characterized in that, The induced resistance The calculation formula is: Drag coefficient of three-dimensional blade section considering equivalent angle of attack correction and induced drag correction for: in, For equivalent angle of attack The corresponding resistance.