A design method for blade power enhancement trailing edge flap

Abstract

The present invention relates to the field of wind power generation, and in particular to a method for designing a blade power-enhancing trailing edge flap, comprising the following steps: calculating the corresponding average operating angle of attack, optimal pitch angle and force distribution of each section of the blade at different wind speeds lower than the rated wind speed; adding flap parameters to the blade airfoil, and judging the optimal flap parameters based on the judgment basis including the average operating angle of attack and the optimal pitch angle; for the airfoil with the optimal flap parameters, modeling and adding groove parameters, and simulating and calculating to obtain the optimal groove parameters; for the airfoil with the optimal groove parameters, determining the flap installation position that meets the safety requirements based on the force distribution. For the 16-25% relative thickness airfoil body near the tip area of ​​the blade toward the outside of the blade span, the lift coefficient and lift-to-drag ratio of the airfoil body can be well improved, and good power-enhancing and noise-reducing effects are achieved.

Description

Technical Field

[0001] The invention relates to the field of wind power generation, and in particular to a design method for a blade power-enhancing trailing edge flap. Background Art

[0002] Wind turbine blades are the main components of wind turbines to capture wind energy, and there are many factors that determine the aerodynamic performance of blades, such as aerodynamic shape, airfoil, structure, etc. The design of blades is mainly based on the optimal aerodynamic performance, and then the structural shape of the blades is optimized through iterative optimization. In order to meet the requirements of blade structural safety, noise control, trailing edge vortex control, etc. when the unit is running, the blades will inevitably sacrifice some aerodynamic performance.

[0003] There are many ways to increase the power of blades, including vortex generators that delay or suppress stall, Gurney flaps that improve trailing edge vortex shedding and increase lift-to-drag ratio, and spoilers. Most of them are to improve the aerodynamic performance of airfoils and blades and improve the ability of blades to capture wind energy by sticking or installing corresponding power-enhancing accessories on the blade surface. Therefore, the aerodynamic optimization design of airfoils and blades and power-enhancing devices have always been one of the research hotspots in the field of wind turbine aerodynamics.

[0004] The installation of flaps on the airfoil and the trailing edge of the blade is widely used in the aviation industry, especially active flaps or ailerons. In wind turbine blades, common forms include trailing edge flat plate, dovetail, Gurney flap, etc., but no detailed design ideas and methods are clear. Summary of the invention

[0005] In view of the problem that there is a lack of clear and detailed flap design method in the prior art, the present invention proposes a blade power enhancement trailing edge flap design method.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for designing a blade power-enhancing trailing edge flap comprises the following steps:

[0008] S1: Calculate the average operating angle of attack, optimal pitch angle and force distribution of each section of the blade at different wind speeds below the rated wind speed;

[0009] S2: adding flap parameters to the blade airfoil, and determining optimal flap parameters based on a determination basis including an average operating angle of attack and an optimal pitch angle;

[0010] S3: For the airfoil with the optimal flap parameters, model and add the groove parameters, and simulate and calculate to obtain the optimal groove parameters;

[0011] S4: For the airfoil with optimal groove parameters, based on the force distribution, determine the flap installation position that meets the safety requirements.

[0012] Furthermore, in step S1:

[0013] Average operating angle of attack and optimal pitch angle: Using GH Bladed software, at wind speed V in ~V rate Wind speed V i Under the above conditions, the average operating angle of attack and the optimal pitch angle of each blade section are calculated. The wind speed interval is 1-2 m / s, V in Indicates the cut-in wind speed, V rate Indicates the wind speed corresponding to the rated power of the wind turbine;

[0014] The force distribution includes flapping force, swing force and lift coefficient.

[0015] Furthermore, the step S2 includes:

[0016] For the airfoil of the blade, 2D calculation is performed by Rfoil software to obtain the Reynolds number Re and Mach number Ma of the airfoil;

[0017] Based on the Reynolds number Re and the Mach number Ma, the lift coefficient Cl and the drag coefficient Cd of the airfoil at different angles of attack α are calculated;

[0018] According to the lift coefficient Cl and drag coefficient Cd, the optimal lift-to-drag ratio C is calculated. best , and obtain the corresponding optimal angle of attack α best

[0019]

[0020] Furthermore, the basis for determining the optimal flap parameters includes:

[0021] Before and after the flaps are installed, the change in the optimal angle of attack corresponding to the best lift-to-drag ratio of the airfoil is less than 2°;

[0022] Before and after the flaps are installed, the change in the optimal pitch angle of each blade section is less than 0.5°;

[0023] Before and after the flaps are installed, the change in the average operating angle of attack of each blade section is less than 0.5°.

[0024] Furthermore, the optimal flap parameters are flap parameters that meet the judgment criteria and have the largest optimal lift-to-drag ratio.

[0025] Furthermore, the attack angle α has a value range of -10° to 20°.

[0026] Furthermore, the simulation calculation of the groove parameters in step S3 includes:

[0027] The airfoil model with groove parameters is meshed using fluid simulation software;

[0028] The best lift-to-drag ratio is obtained through transient and steady-state calculations;

[0029] When the optimal lift-to-drag ratio is the largest, the corresponding groove parameters are the optimal groove parameters.

[0030] Furthermore, the step S4 includes:

[0031] According to the force distribution, preliminarily determine the installation starting position Xstart and the end position Xend of the flap;

[0032] GH Bladed software is used to calculate the safety of the whole machine load. If the safety requirements are met, the design is completed. If the safety requirements are not met, the installation starting position Xstart and the end position Xend are optimized, and the safety of the whole machine load is calculated again.

[0033] Further, the flap parameters include flap length, flap thickness, downward angle, wedge angle and wedge length in the wedge-shaped structure shape;

[0034] The groove parameters include groove width, groove depth, groove length and groove slope.

[0035] Furthermore, edge sealing is provided on both sides of the flap installation position.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] First, the present invention has made arrangements for the entire design process from airfoil design, aerodynamic performance calculation, layout position analysis, load calculation and safety review, and rationally designs the structural shape of the flap, improves the aerodynamic performance of the blade, and increases the ability to capture wind energy; the calculation method is simple, efficient and highly accurate; the grooves are designed to increase the surface area of ​​the flap in contact with the airflow, and the grooves at the farthest end of the flap will generate a wingtip vortex of a certain strength, which has a good destructive effect on the trailing edge shedding vortex and reduces the induced drag loss.

[0038] Second, a new edge sealing design is added to the start and end positions of the flap to avoid or reduce the induced drag loss caused by sudden shape changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0040] In the attached picture:

[0041] Figure 1A top view of a blade power enhancement trailing edge flap design method according to the present invention for adding flaps to an airfoil;

[0042] Figure 2 It is a side view of an airfoil of a blade power enhancement trailing edge flap design method of the present invention;

[0043] Figure 3 It is a schematic diagram of the overall process of a blade power enhancement trailing edge flap design method of the present invention;

[0044] Figure 4 It is a schematic diagram of a process flow of a blade power enhancement trailing edge flap design method of the present invention;

[0045] Figure 5 A blade power enhancement trailing edge flap design method of the present invention is a flap-adding coordinate diagram for an airfoil;

[0046] Figure 6 1 is a diagram showing lift calculation results of NACA63421 Rfoil with different shapes in Example 2 of the present invention;

[0047] Figure 7 Schematic diagram of the variation trend of lift-to-drag ratio of NACA63421 airfoil with flap length in Example 2 of the present invention;

[0048] Figure 8 Schematic diagram of flap installation position based on lift coefficient in Embodiment 2 of the present invention;

[0049] Fig. 9 Schematic diagram of flap installation position based on flapping load in embodiment 2 of the present invention;

[0050] Fig.10 This is an enlarged view of an airfoil equipped with a flap according to a method for designing a blade power-enhancing trailing edge flap according to the present invention.

[0051] In the figure, 1-blade, 2-flap, 3-edge sealing, 4-groove. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0053] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0054] Wind turbines capture wind energy through wind rotors. As the main component of wind rotors, the aerodynamic performance of blades will directly affect the wind turbine's ability to capture wind energy. The aerodynamic performance of blades is determined by airfoil distribution, airfoil aerodynamic performance, twist angle, chord length, thickness and other parameters. Figure 1 and Figure 2 As shown, flap 2 is installed at the trailing edge of airfoil 1, and increases the wind energy capture capability of the blade by increasing the cross-sectional chord length of the blade and the pressure difference between the upper and lower airfoil surfaces. The main principle is that the spanwise position of the blade where the flap is located is on the outside of the blade, closer to the tip area. The main characteristics of this area are: the main output position of the blade; the relative thickness of the airfoil is relatively thin, 18% to 25%; the linear speed is large; the airflow on the airfoil surface is mostly not separated; and the airfoil has better aerodynamic performance.

[0055] Example 1

[0056] like Figure 3 As shown, a method for designing a blade power enhancement trailing edge flap comprises the following steps:

[0057] Step 1: Calculate the average operating angle of attack and force distribution corresponding to each cross-sectional position of the blade at each wind speed lower than the rated wind speed;

[0058] Step 2: Design and calculate the flap shape and parameters by averaging the operating angle of attack;

[0059] Step 3: Calculate the optimal groove parameters through the flap shape and parameters;

[0060] Step 4: Determine the flap installation position that meets safety requirements based on the optimal groove parameters and the force distribution in step 1.

[0061] Specific steps are as follows Figure 4 shown.

[0062] The step 1 comprises the following:

[0063] The GH Bladed software is used to calculate the average operating angle of attack and force distribution corresponding to each cross-sectional position of the blade at wind speeds below the rated wind speed.

[0064] Step 11: For the standard specific airfoil used for wind turbine blades, use GH Bladed software to calculate the wind speed V in ~V rate Wind speed V i Under the condition of , the average operating angle of attack and the optimal pitch angle of each section of the blade are calculated within a certain period of time. The wind speed interval is 1-2m / s, V in Indicates the cut-in wind speed, V rate Indicates the wind speed corresponding to the rated power;

[0065] Step 12: At each wind speed V iUnder this condition, the force distribution of each section of the blade is calculated, including the flapping direction force F flapforce , swing direction force F edgeforce and the lift coefficient Cl i ,like Figure 8 and Fig. 9 As shown, there are lift coefficient curves and flapping direction force curves at each cross-sectional position of the blade;

[0066] The step 2 includes the following:

[0067] Step 21: Perform 2D calculations on the standard specific airfoil used for wind turbine blades using the Rfoil software to obtain the Reynolds number Re and the Mach number Ma. The calculations must take into account the influence of air density, temperature, humidity, and rotor speed. The formula is as follows:

[0068]

[0069] Where ρ represents air density, v represents airflow velocity, l represents airfoil characteristic length, and υ represents dynamic viscosity coefficient;

[0070]

[0071] Where a is the speed of sound in air.

[0072] Step 22: Based on the Reynolds number Re and the Mach number Ma determined in step 21, calculate the lift coefficient Cl and the drag coefficient Cd of the airfoil at different angles of attack α, where the angle of attack α ranges from -10° to 20°.

[0073] Step 23: Calculate the optimal lift-to-drag ratio C based on the lift coefficient Cl and drag coefficient Cd. best , and the corresponding optimal angle of attack α is obtained best , the formula is as follows:

[0074]

[0075] Step 24: Based on Rfoil or Xfoil software, by adjusting the coordinate values ​​of the pressure surface and suction surface of the trailing edge area of ​​the wind turbine blade airfoil, different flap parameters are obtained to achieve different flap lengths, wedge structures, thicknesses, downward angles and other basic parameter changes, corresponding to different flap aerodynamic shapes. When calculating, the coordinate values ​​need to be normalized. Figure 5 As shown, the trailing edge area of ​​the wind turbine blade airfoil is projected two-dimensionally onto the coordinate axis.

[0076] Step 25: For the above different flap parameters, determine the optimal flap parameters according to the judgment basis, and obtain the optimal aerodynamic shape after the airfoil is equipped with flaps;

[0077] The basis for evaluating whether the flap parameters are optimal is:

[0078] Before and after the flaps are installed, the change in the optimal angle of attack corresponding to the optimal lift-to-drag ratio of the airfoil is less than 2°, that is, |α best- α' best |≤θ,θ=2°,α' best The optimal angle of attack of the airfoil after the flaps are installed is to prevent the drag coefficient from increasing too much and reduce the risk of stalling;

[0079] Before and after the flaps are installed, the change in the optimal pitch angle of each blade section is less than 0.5°;

[0080] Before and after the flaps are installed, the change in the average operating angle of attack of each section of the blade is less than 0.5°, |α' n -α n |≤0.5°,α' n It is the average operating angle of attack of each section of the blade after the flaps are installed, to avoid the fluctuation of the rotation speed after the trailing edge flaps are installed;

[0081] After satisfying the above three criteria, the best lift-to-drag ratio is selected, i.e. C' best The flap parameter corresponding to the maximum is the optimal flap parameter.

[0082] The optimal flap parameters include flap length, flap thickness, flap down angle, wedge angle and wedge length in the wedge-shaped structure;

[0083] Step 3: Based on the above airfoil with optimal flap parameters, groove parameters are added and the optimal groove parameters are calculated. The groove parameters include groove width, groove depth, groove length and groove slope;

[0084] Step 31: Use 3D software to create a 3D model of the airfoil with optimal flap parameters, such as Fig.10 As shown, a plurality of grooves 4 are provided on the lower surface of the flap 2, i.e., the non-bonding surface side, along the airflow direction, to obtain a slotted airfoil model;

[0085] Step 32: Use professional CFD fluid simulation software to mesh the slotted airfoil model, and obtain the optimal lift-to-drag ratio of the slotted airfoil through transient and steady-state calculations;

[0086] Step 33: Optimize the groove parameters. Execute step 32 again. When the optimal lift-to-drag ratio of the slotted airfoil is the largest, the corresponding groove parameters are the optimal groove parameters.

[0087] Step 4: Determine the flap installation position that meets safety requirements based on the optimal groove parameters and the force distribution in step 1, including:

[0088] Step 41: Preliminarily determine the installation start position Xstart and end position Xend of the flap according to the force distribution of each cross section of the blade in step 12;

[0089] Step 42: Use GH Bladed software to calculate the safety of the whole machine load. If the safety requirements are met, the design is completed; if the safety requirements are not met, optimize the installation starting position Xstart and the end position Xend, and calculate the safety of the whole machine load again.

[0090] Preferably, for the commonly used DU series, NACA series and other optimized airfoils of wind turbines, the recommended flap length range is 40mm to 70mm, the flap thickness is less than or equal to the original blade trailing edge thickness, the wedge angle range is 10 to 45°, the wedge length range is 0.25*L1 to 0.35*L1, and the downward flip angle range is 4 to 9°; the groove length is greater than or equal to the flap length, the groove width range is 2 to 10mm, the groove depth is less than or equal to the flap thickness, and the inclination range is 85 to 95°.

[0091] Preferably, both sides of the flap's installation starting position Xstart and end position Xend are designed with edge sealing shapes to reduce shedding vortices formed by sudden changes in shape and reduce induced drag.

[0092] The grooves of the flaps increase the force-bearing area to further optimize the lifting effect, while the wake shedding vortex at the trailing edge of the flaps also has a certain noise reduction effect.

[0093] Flaps can be mounted on the pressure side of the airfoil or blade body, or on the suction side.

[0094] The installation and fixing method can be bonding, riveting, bolting, etc.

[0095] Example 2

[0096] Taking the NACA63421 airfoil as an example, the dimensions of the flaps and grooves are designed and calculated according to the content of the present invention. The lift calculation results of Rfoil with different shapes are as follows: Figure 6 As shown in the figure, Mach = 0.15, Re = 3E6. The calculation of the flap down angle, thickness, and wedge-shaped structure shape is the same as in Example 1. The trend of the airfoil lift-drag ratio with the flap length is as follows Figure 7 shown.

[0097]

[0098]

[0099]

[0100] The determined flap dimensions and NACA63421 airfoil structure are modeled in 3D modeling software, the surface groove dimensions are designed, and meshing, steady-state calculations and transient calculations are iterated through professional fluid calculation software to obtain the optimal groove parameters and aerodynamic effects.

[0101] The final calculation results show that after the NACA63421 airfoil is equipped with a flap with grooves, the optimal lift-to-drag ratio is increased from the original 145.1 to 168.8, an increase of 16.33%.

[0102] The wind turbine load simulation software GH Bladed is used to calculate the forces and lift coefficient distribution of each section of a 1.5MW blade in the flapping and swinging directions at wind speeds of 3 to 11 m / s. Figure 8 and Fig. 9 As shown, there are lift coefficient curves and flapping direction force curves at various cross-sectional positions of the blade.

[0103] Based on the distribution of flapping, shimmy and lift coefficient sections, as well as the safety verification conclusions of all components after load calculation, the final recommendation for the installation position of the flap is 27 to 39 meters. According to the wind frequency distribution of A = 6m / s and k = 2Weibull, it is calculated that the annual power generation of the unit will increase by 2.1% after the flap is installed.

[0104] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for designing a blade power enhancement trailing edge flap, characterized in that: The steps include: S1: Calculate the average operating angle of attack, optimal pitch angle and force distribution of each section of the blade at different wind speeds below the rated wind speed; S2: adding flap parameters to the blade airfoil, and determining optimal flap parameters based on a determination basis including an average operating angle of attack and an optimal pitch angle; S3: For the airfoil with the optimal flap parameters, model and add the groove parameters, and simulate and calculate to obtain the optimal groove parameters; S4: for the airfoil with the optimal groove parameters, determining a flap installation position that meets safety requirements based on the force distribution; In step S1: Average operating angle of attack and optimal pitch angle: Using GH Bladed software, at wind speed V in ~V rate Wind speed V i Under the wind speed, the average operating angle of attack and the optimal pitch angle of each section of the blade are calculated. The wind speed interval is 1-2m / s, V in Indicates the cut-in wind speed, V rate Indicates the wind speed corresponding to the rated power of the wind turbine; The force distribution includes flapping force, swing force and lift coefficient.

2. The blade power enhancement trailing edge flap design method according to claim 1, characterized in that: The step S2 includes: For the airfoil of the blade, the Reynolds number Re and the Mach number Ma of the airfoil are obtained; Based on the Reynolds number Re and the Mach number Ma, 2D calculation is performed by Rfoil software to calculate the lift coefficient Cl and the drag coefficient Cd of the airfoil at different angles of attack α; According to the lift coefficient Cl and drag coefficient Cd, the optimal lift-to-drag ratio C is calculated. best , and obtain the corresponding optimal angle of attack α best 3. The blade power enhancement trailing edge flap design method according to claim 2, characterized in that: The basis for determining the optimal flap parameters includes: Before and after the flaps are installed, the change in the optimal angle of attack corresponding to the best lift-to-drag ratio of the airfoil is less than 2°; Before and after the flaps are installed, the change in the optimal pitch angle of each blade section is less than 0.5°; Before and after the flaps are installed, the change in the average operating angle of attack of each blade section is less than 0.5°.

4. The blade power enhancement trailing edge flap design method according to claim 3, characterized in that: The optimal flap parameters are flap parameters that meet the judgment criteria and have the largest optimal lift-to-drag ratio.

5. The blade power enhancement trailing edge flap design method according to claim 2, characterized in that: The attack angle α has a value range of -10° to 20°.

6. The blade power enhancement trailing edge flap design method according to claim 1, characterized in that: The simulation calculation of the groove parameters in step S3 includes: The airfoil model with groove parameters is meshed using fluid simulation software; The best lift-to-drag ratio is obtained through transient and steady-state calculations; When the optimal lift-to-drag ratio is the largest, the corresponding groove parameters are the optimal groove parameters.

7. The blade power enhancement trailing edge flap design method according to claim 1, characterized in that: The step S4 includes: According to the force distribution, preliminarily determine the installation starting position Xstart and the end position Xend of the flap; GH Bladed software is used to calculate the safety of the whole machine load. If the safety requirements are met, the design is completed. If the safety requirements are not met, the installation starting position Xstart and the end position Xend are optimized, and the safety of the whole machine load is calculated again.

8. The method for designing a blade power enhancement trailing edge flap according to claim 1, characterized in that: The flap parameters include flap length, flap thickness, downward angle, wedge angle and wedge length in the wedge-shaped structure; The groove parameters include groove width, groove depth, groove length and groove slope.

9. The blade power enhancement trailing edge flap design method according to claim 1, characterized in that: There are edge banding on both sides of the flap installation location.

Images