A method for determining the optimal rotor speed of a twin-rotor horizontal axis wind turbine

Abstract

The present invention proposes a method for determining the optimal rotor speed of a twin-rotor horizontal-axis wind turbine. The method determines the optimal upstream rotor speed and downstream rotor speed of the wind turbine by simulating the wind field formed by the mutual influence between the upstream rotor and the downstream rotor of the twin-rotor wind turbine given a given inflow wind speed. When calculating the speed of the upstream rotor, the relationship curve between the rotor tip speed ratio and the power coefficient is first simulated, and the optimal tip speed ratio is determined according to the maximum value of the relationship curve; then, the optimal speed of the upstream rotor is determined according to the relationship between the inflow wind speed, the tip speed ratio and the speed; when calculating the speed of the downstream rotor, the inflow wind speed in front of the downstream rotor is first simulated, and then the effective inflow wind speed is calculated according to the wind speed distributed on its rotating surface, and the optimal speed of the downstream rotor is determined according to the relationship between the effective inflow wind speed, the tip speed ratio and the speed. While ensuring the accuracy of the determination of the optimal speed, the present invention also takes into account the efficiency of the determination of the optimal speed.

Description

Technical Field

[0001] The present invention relates to the technical field of aerodynamic performance of wind turbines, and in particular to a method for determining an optimal wind rotor speed of a twin-rotor horizontal-axis wind turbine. Background Art

[0002] The wind power industry is a vital component of the renewable energy sector. To enable wind turbines to capture more wind energy, they are currently being developed towards deeper, deeper-sea installations and larger sizes. As early as 2016, a design for a 20 MW wind turbine with a rotor diameter of 276m and a maximum power coefficient of 0.48 was already available. However, larger wind turbines mean higher manufacturing and maintenance costs. Larger blades also place greater loads on the blade roots and gearbox, shortening their service life. Therefore, research into new wind turbine configurations to reduce costs and improve wind energy capture efficiency is essential. Tandem twin-rotor wind turbines are a key focus of this new wind turbine research. Compared to the theoretical maximum power coefficient of 0.593 for traditional single-rotor wind turbines, tandem twin-rotor wind turbines can achieve a theoretical maximum power coefficient of 0.64. Traditional single-rotor wind turbines typically only have a power coefficient between 0.4 and 0.5 in actual operation. In order to break through the theoretical and actual limits of wind energy capture efficiency of traditional single-rotor wind turbines, research on various design parameters of dual-rotor wind turbines has become a current research hotspot.

[0003] Tandem twin-rotor wind turbines fall under the research umbrella of new wind turbine configurations. The primary goal of this research is to analyze their aerodynamic performance through numerical simulation, experimental verification, or theoretical derivation, thereby better guiding wind turbine design and structural optimization. Most research on this new type of wind turbine builds models or selects parameters based on existing wind turbine parameters. For example, single-rotor wind turbines are combined to create a complete twin-rotor system, with key parameters such as rotor speed and size directly adopting those of single-rotor wind turbines. However, when a twin-rotor wind turbine is operating, the speeds of its upstream and downstream rotors significantly impact the wind energy capture efficiency of the wind power generation system. Therefore, accurately determining the optimal speeds of the upstream and downstream rotors is crucial for studying the aerodynamic performance of twin-rotor wind turbines and improving their wind energy capture efficiency.

[0004] Therefore, it is necessary to clarify a method for determining the optimal speed of the upstream and downstream wind rotors of a dual-rotor wind turbine to provide certain technical guidance for the aerodynamic performance evaluation and improvement of wind energy capture efficiency of this configuration of wind turbine. Summary of the Invention

[0005] This paper proposes a method for determining the optimal rotor speed for a twin-rotor horizontal-axis wind turbine. This method accounts for the interaction between the upstream and downstream rotors and is applicable to twin-rotor wind turbine configurations with varying rotor spacing and rotor radius ratios. This method, combined with the blade design and analysis software QBlade and the finite element simulation software Fluent, ensures both accuracy and efficiency in determining the optimal speed.

[0006] The present invention adopts the following technical solutions.

[0007] A method for determining the optimal rotor speed of a twin-rotor horizontal-axis wind turbine, wherein the method determines the optimal upstream rotor speed and downstream rotor speed of the wind turbine by simulating the wind field formed by the mutual influence between the upstream rotor and the downstream rotor of the twin-rotor wind turbine given an inflow wind speed. When calculating the upstream rotor speed, a curve of the relationship between the rotor tip speed ratio and the power coefficient is first simulated, and the optimal tip speed ratio is determined according to the maximum value of the relationship curve; then, the optimal speed of the upstream rotor is determined according to the relationship between the inflow wind speed, the tip speed ratio and the speed; when calculating the downstream rotor speed, the inflow wind speed in front of the downstream rotor is first simulated, and then the effective inflow wind speed is calculated according to the wind speed distributed on its rotating surface, and the optimal speed of the downstream rotor is determined according to the relationship between the effective inflow wind speed, the tip speed ratio and the speed.

[0008] The method is implemented based on blade design software QBlade and Fluent finite element analysis.

[0009] The method comprises the following steps:

[0010] Step S1: Creating a geometric model of a wind turbine rotor in QBlade based on airfoil data;

[0011] Step S2: Obtain the lift coefficient and drag coefficient within the full angle of attack range of the blade airfoil to complete the blade modeling;

[0012] Step S3: Given the inflow wind speed in front of the upstream wind rotor, a relationship curve between the wind rotor tip speed ratio and the power coefficient is obtained through QBlade simulation. According to the relationship curve, the maximum value is determined as the optimal tip speed ratio;

[0013] Step S4: determining the optimal rotational speed of the upstream wind wheel by using the relationship between the inflow wind speed, the tip speed ratio and the rotational speed;

[0014] Step S5: Establish a geometric model and computational domain of a dual-rotor wind turbine for solving in Fluent, complete meshing, and input the upstream rotor speed as a boundary condition;

[0015] Step S6: In the Fluent simulation software, the upstream wind rotor is rotated at an optimal speed and the downstream wind rotor is stationary. The inflow wind speed in front of the downstream wind rotor is obtained by simulation. The effective inflow wind speed is calculated based on the wind speed distributed on the rotating surface of the downstream wind rotor.

[0016] Step S7: determining the optimal rotational speed of the downstream wind rotor according to the relationship between the effective inflow wind speed of the downstream wind rotor, the tip speed ratio and the rotational speed.

[0017] In step S1, establishing a blade geometry model in QBlade includes importing airfoil coordinate parameters, and importing structural parameters of airfoil chord length, twist angle, and cross-sectional position.

[0018] In step S2, the lift coefficient and drag coefficient of different airfoils in the full range of attack angles are obtained by solving in QBlade.

[0019] In step S3, a schematic diagram of the change of the wind rotor tip speed ratio and the power coefficient is first obtained through QBlade simulation, and then a relationship curve is obtained from the diagram.

[0020] The method from step S5 to step S7 simulates the wind field changes between the wind rotors of the dual-rotor wind turbine based on finite element simulation.

[0021] The accuracy of calculating the optimal speed of the downstream wind wheel is ensured by improving the accuracy of calculating the effective inflow wind speed of the downstream wind wheel.

[0022] The calculation formula for the effective inflow wind speed of the downstream wind wheel is:

[0023]

[0024] V e is the effective inflow wind speed, V 1 to V n is the finite element simulation result of the wind speed at each point on the rotating surface of the downstream wind rotor, n is the number of grid points.

[0025] The wind turbine is a tandem double-rotor wind turbine.

[0026] The optimal rotational speed determination method provided by the present invention can achieve the following beneficial effects: without the need for repeated iterations of finite element simulation modeling and calculation processes, the optimal tip speed ratio of various wind turbine rotors can be quickly calculated through the QBlade software developed based on BEM, facilitating the determination of the optimal rotational speed; based on finite element simulation, the wind field formed by the mutual influence between the upstream and downstream rotors of a dual-rotor wind turbine is simulated, and the calculated effective inflow wind speed of the downstream rotor ensures the accuracy of the downstream rotor rotational speed determination result. It can be applied to dual-rotor wind turbines with any rotor spacing, number of rotor blades, and upstream and downstream rotor radius ratio. It lays the foundation for determining the input rotational speed when studying the aerodynamic performance of dual-rotor wind turbines. The optimal rotor rotational speed determined according to the present invention also further improves the wind turbine's wind energy capture rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] Attachment Figure 1 It is a schematic flow chart of the method of the present invention;

[0029] Attachment Figure 2 It is a schematic diagram of the relationship between the wind rotor power coefficient and its tip speed ratio and the wind rotor size;

[0030] Attachment Figure 3 This is a schematic diagram of a two-blade dual-rotor wind turbine structure used in an example of a specific embodiment;

[0031] Attachment Figure 4 This is a schematic diagram of the calculation domain used to solve the downstream wind rotor inflow wind speed in finite element analysis;

[0032] Attachment Figure 5 It is a schematic diagram of the downstream wind rotor rotating surface and the wind speed distribution on the rotating surface;

[0033] Figure 3 Middle: 1 upstream wind rotor, 2 downstream wind rotor, 3 nacelle tower part. DETAILED DESCRIPTION

[0034] As shown in the figure, a method for determining the optimal rotor speed of a twin-rotor horizontal-axis wind turbine is provided. The method determines the optimal upstream rotor speed and downstream rotor speed of the wind turbine by simulating the wind field formed by the mutual influence between the upstream rotor 1 and the downstream rotor 2 of the twin-rotor wind turbine given an inflow wind speed. When calculating the upstream rotor speed, the relationship curve between the rotor tip speed ratio and the power coefficient is first simulated, and the optimal tip speed ratio is determined according to the maximum value of the relationship curve; then, the optimal speed of the upstream rotor is determined according to the relationship between the inflow wind speed, the tip speed ratio and the speed; when calculating the downstream rotor speed, the inflow wind speed in front of the downstream rotor is first simulated, and then the effective inflow wind speed is calculated according to the wind speed distributed on its rotating surface, and the optimal speed of the downstream rotor is determined according to the relationship between the effective inflow wind speed, the tip speed ratio and the speed.

[0035] The method is implemented based on blade design software QBlade and Fluent finite element analysis.

[0036] The method comprises the following steps:

[0037] Step S1: Creating a geometric model of a wind turbine rotor in QBlade based on airfoil data;

[0038] Step S2: Obtain the lift coefficient and drag coefficient within the full angle of attack range of the blade airfoil to complete the blade modeling;

[0039] In this step, wind rotor blades of all sizes and types can be used;

[0040] Step S3: Given the inflow wind speed in front of the upstream wind rotor, a relationship curve between the wind rotor tip speed ratio and the power coefficient is obtained through QBlade simulation. According to the relationship curve, the maximum value is determined as the optimal tip speed ratio;

[0041] In this step, the inflow wind speed in front of the upstream wind rotor is given as 9m / s. The schematic diagram of the change of the wind rotor tip speed ratio and power coefficient is obtained through QBlade simulation as shown in the following figure: Figure 2 As shown in the figure R 0 represents a wind wheel with a different radius ratio to the downstream wind wheel. According to the relationship curve, the maximum value determines the optimal tip speed ratio;

[0042] Step S4: determining the optimal rotational speed of the upstream wind wheel by using the relationship between the inflow wind speed, the tip speed ratio and the rotational speed;

[0043] Step S5: Establish a geometric model and computational domain of a dual-rotor wind turbine for solving in Fluent, complete meshing, and input the upstream rotor speed as a boundary condition;

[0044] In this step, the geometric model of the twin-rotor wind turbine generator for solution is established in Fluent. Figure 3 and computational domains such as Figure 4As shown in the figure D is the diameter of the downstream rotor. Complete the meshing and input the upstream rotor speed as the boundary condition.

[0045] Step S6: In the Fluent simulation software, the upstream wind rotor is rotated at an optimal speed and the downstream wind rotor is stationary. The inflow wind speed in front of the downstream wind rotor is obtained by simulation. The effective inflow wind speed is calculated based on the wind speed distributed on the rotating surface of the downstream wind rotor.

[0046] In this step, the wind speed distributed on the rotating surface of the downstream wind wheel is as follows: Figure 5 As shown;

[0047] Step S7: determining the optimal rotational speed of the downstream wind rotor according to the relationship between the effective inflow wind speed of the downstream wind rotor, the tip speed ratio and the rotational speed.

[0048] In step S1, establishing a blade geometry model in QBlade includes importing airfoil coordinate parameters, and importing structural parameters of airfoil chord length, twist angle, and cross-sectional position.

[0049] In step S2, the lift coefficient and drag coefficient of different airfoils in the full range of attack angles are obtained by solving in QBlade.

[0050] In step S3, a schematic diagram of the change of the wind rotor tip speed ratio and the power coefficient is first obtained through QBlade simulation, and then a relationship curve is obtained from the diagram.

[0051] The method from step S5 to step S7 simulates the wind field changes between the wind rotors of the dual-rotor wind turbine based on finite element simulation.

[0052] The accuracy of calculating the optimal speed of the downstream wind wheel is ensured by improving the accuracy of calculating the effective inflow wind speed of the downstream wind wheel.

[0053] The calculation formula for the effective inflow wind speed of the downstream wind wheel is:

[0054]

[0055] V e is the effective inflow wind speed, V 1 to V n is the finite element simulation result of the wind speed at each point on the rotating surface of the downstream wind rotor, n is the number of grid points.

[0056] The wind turbine is a tandem double-rotor wind turbine.

[0057] In this example, a two-blade tandem twin-rotor wind turbine is selected for speed calculation. Tandem twin-rotor wind turbines with other blade numbers, sizes, and rotor spacings can also be used. The finite element analysis in this article was performed using ANSYS Fluent, but other finite element analysis software suitable for fluid simulation can also be used.

Claims

1. A method for determining the optimal rotor speed of a twin-rotor horizontal axis wind turbine, characterized by: The method comprises the following steps: Step S1: Creating a geometric model of a wind turbine rotor in QBlade based on airfoil data; Step S2: Obtain the lift coefficient and drag coefficient within the full angle of attack range of the blade airfoil to complete the blade modeling; Step S3: Given the inflow wind speed in front of the upstream wind rotor, a relationship curve between the wind rotor tip speed ratio and the power coefficient is obtained through QBlade simulation. According to the relationship curve, the maximum value is determined as the optimal tip speed ratio; Step S4: determining the optimal rotational speed of the upstream wind wheel by using the relationship between the inflow wind speed, the tip speed ratio and the rotational speed; Step S5: Establish a geometric model and computational domain of a dual-rotor wind turbine for solving in Fluent, complete meshing, and input the upstream rotor speed as a boundary condition; Step S6: In the Fluent simulation software, the upstream wind rotor is rotated at an optimal speed and the downstream wind rotor is stationary. The inflow wind speed in front of the downstream wind rotor is simulated and the effective inflow wind speed is calculated based on the wind speed distributed on the rotating surface of the downstream wind rotor. Step S7: determining the optimal speed of the downstream wind rotor according to the relationship between the effective inflow wind speed of the downstream wind rotor, the tip speed ratio and the speed; In step S1, the blade geometry model is established in QBlade, including importing airfoil coordinate parameters, importing airfoil chord length, twist angle and cross-section position structural parameters; In step S2, the lift coefficient and drag coefficient of different airfoils in the full range of attack angles are obtained by solving in QBlade; In step S3, a schematic diagram of the change of the wind rotor tip speed ratio and the power coefficient is first obtained through QBlade simulation, and then a relationship curve is obtained from the diagram; The method of steps S5 to S7 simulates the wind field changes between the wind rotors of the dual-rotor wind turbine based on finite element simulation; The calculation formula for the effective inflow wind speed of the downstream wind wheel is: V e is the effective inflow wind speed, V 1 to V n is the finite element simulation result of the wind speed at each point on the rotating surface of the downstream wind rotor, n is the number of grid points.

2. The method for determining the optimal rotor speed of a twin-rotor horizontal axis wind turbine according to claim 1, characterized in that: The wind turbine is a tandem double-rotor wind turbine.

3. The method for determining the optimal rotor speed of a twin-rotor horizontal axis wind turbine according to claim 1, characterized in that: The method is implemented based on blade design software QBlade and Fluent finite element analysis.

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