A three-dimensional wake model of an offshore floating wind turbine

Abstract

The present invention relates to the technical field of wind farm data analysis, and in particular, to a three-dimensional wake model of an offshore floating wind turbine, comprising the following steps: S1: adding a wake Gaussian function distribution and vertical wind shear to construct a wake model of a wind turbine without wave action, which is named a three-dimensional Jensen-Gaussian (3DJG) model; S2: in the 3DJG wake model, the position movement of the floating unit platform caused by wave motion is converted into a transformation of three-dimensional coordinates; S3: on the basis of an improved yaw wake model, the deflection angle of the wind wheel plane and the vertical direction caused by wave motion is converted into a wake offset, and added to the z direction of the model after the three-dimensional transformation, to obtain a 3D-OFWT model of a floating wind turbine under wind and wave action. The present invention aims to obtain input information of a downstream flow field and provide a reference for dynamic load analysis of a downstream wind turbine. It can be applied to actual wind farms, provide guidance for the prediction of wind power in floating wind farms and the design of unit control and operation strategies, improve wind turbine performance, and increase energy output.

Description

Technical Field

[0001] The present invention relates to the technical field of wind field data analysis, and in particular to a three-dimensional wake model of an offshore floating wind turbine. Background Art

[0002] The existing wind farms are large in scale, occupy a large area, have large wind turbines and are in a complex environment, which brings many problems to the wind farms that need to be solved urgently. Among them, the wake interference effect between wind turbines has always been a hot research topic. With the saturation of the available area in the onshore wind resource-rich areas, wind turbines are gradually moving towards the deep sea. Compared with onshore units and offshore fixed units, the working environment of offshore floating units is more complex. The unique motion characteristics of the floating platform make the distribution of the flow field more difficult to predict, and the effect of the wave-coupled atmospheric environment on the wind turbine makes the velocity analysis in the wake area more difficult. The large-scale wind farms and units further aggravate the wake effect, which has a more significant impact on the life of wind turbines, and the cost of offshore floating units is higher. Therefore, the use of mathematical models to characterize the wake of floating wind turbines is of great significance to the layout optimization and economic operation of wind farms. The present invention proposes a three-dimensional wake model of an offshore floating wind turbine to study the spatial distribution characteristics of the entire wake area behind the wind rotor plane. Summary of the invention

[0003] In view of this, the present invention provides a three-dimensional wake model of an offshore floating wind turbine, which can achieve high-accuracy prediction of the wake wind speed of the offshore wind farm wind turbine.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A three-dimensional wake model of an offshore floating wind turbine, characterized in that it provides guidance for the wind power prediction of a floating wind farm and the design of a unit control operation strategy, improves the performance of the wind turbine, and increases energy output, comprising the following steps:

[0006] S1. Add the wake Gaussian function distribution and vertical wind shear to construct the wake model of the wind turbine without wave action, and name it the three-dimensional Jensen-Gaussian (3DJG) model;

[0007] S2. In the 3DJG wake model, the position movement of the floating unit platform caused by wave motion is converted into a transformation of three-dimensional coordinates;

[0008] S3. On the basis of the improved yaw wake model, the deflection angle between the rotor plane and the vertical direction caused by wave motion is converted into a wake offset and added to the z direction of the three-dimensional transformed model to obtain the 3D-OFWT model of the floating wind turbine under wind and wave action.

[0009] Furthermore, the calculation formula of the wake model of the wind turbine without wave action in step S1 is as follows:

[0010]

[0011] Among them, u ref is at the reference height z ref The wind speed of the incoming wind detected at the location; hub is the center height of the wind turbine hub; z+z hub is the height from the ground; α is the wind shear index; axial induction factor C T is the axial thrust coefficient; r 0 is the initial wake radius; r z is the wake radius in the vertical direction; σ z is the standard deviation of the Gaussian distribution in the vertical direction; σ y is the standard deviation of the Gaussian distribution in the horizontal direction;

[0012] Furthermore, the calculation formulas for the radii of the wake in the horizontal plane and the vertical plane are as follows:

[0013]

[0014] Among them, the anisotropic wake expansion coefficient is used, and the calculation formula is:

[0015]

[0016] Furthermore, in step S2, the yaw wake model is improved to decompose the thrust on the wind turbine in the x and z directions. The calculation formula is as follows:

[0017]

[0018] Furthermore, the wind momentum m in front of the fan in the control body 1 , the momentum lost by the impeller m 2 The sum of the ambient wind momentum absorbed by the wake m 3 It is equal to the wind momentum at the interface x=n on the wake. The calculation formula using the momentum conservation equation and mass conservation equation is as follows:

[0019]

[0020] Furthermore, the value of the assumption β is extremely small, and the calculation formula is as follows:

[0021]

[0022] Furthermore, the calculation formula for the offset of the wind turbine wake center is as follows:

[0023]

[0024] Furthermore, in step S3, the deflection angle between the rotor plane and the vertical direction caused by the wave motion is converted into a wake offset, and added to the z direction of the three-dimensional transformed model to obtain a 3D-OFWT model of a floating wind turbine under wind and wave action. The calculation formula is as follows:

[0025]

[0026] Among them, σ y =[k y (x-x'+z hub cosθ 2 sinθ 1 )+r 0 ] / 2.58; r z =k z (x-x'+z hub cosθ 2 sinθ 1 )+r 0 .

[0027] Through the above technical solutions, it can be seen that compared with the prior art, the present invention provides a three-dimensional wake model of an offshore floating wind turbine: the present invention has reasonable derivation and simple calculation. It has been improved on the basis of the method of processing the deflection angle in the existing yaw wake model, and combined with the advantages of the 3DJG wake model, it can better describe the wake distribution characteristics behind the floating wind turbine under different working conditions, and can provide a reference for the dynamic load analysis of the downstream wind turbine. It can be applied to actual wind farms, provide guidance for the wind power prediction and unit control operation strategy design of floating wind farms, improve the performance of wind turbines, and increase energy output. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0029] Figure 1 A schematic diagram of a flow chart of a three-dimensional wake model of an offshore floating wind turbine provided by the present invention;

[0030] Figure 2 A three-dimensional coordinate system diagram of the wake model provided by the present invention;

[0031] Figure 3A schematic diagram showing the comparison results of the 3D-OFWT wake model provided by the present invention with different wind tunnel measured data and other wake models;

[0032] Figure 4 Schematic diagram of the velocity distribution results in the wake region of the 3D-OFWT wake model provided by the present invention under different turbulence intensities. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides an embodiment, which mainly includes the following steps:

[0035] S1. Establish the 3DJG wake model of the wind turbine without wave action;

[0036] S2, transforming the platform position movement into three-dimensional coordinates;

[0037] S3. Convert the deflection angle into wake offset to obtain the 3D-OFWT model.

[0038] The specific process is as follows Figure 1 shown.

[0039] In step S1, a wake model of a wind turbine without wave action is established, and the establishment process is as follows:

[0040] In order to accurately describe the wind speed distribution in the wake area, Figure 2 As shown, the offshore floating wind turbine is taken as a reference when it is not affected by waves and swells and is at the starting position of a wave cycle ( Figure 1 The hub center is taken as the origin of the coordinate system. The x direction represents the axial direction extending from the incident wind to the wake direction. The y direction represents the horizontal direction perpendicular to the x-axis. The z direction represents the vertical direction perpendicular to the xoy plane. The wake wind speed is defined as u(x,y,z), which is abbreviated as u.

[0041] In the derivation of the model, the wake width was first determined based on the accuracy characteristics of the Gaussian function. From the properties of the standard density function curve of the one-dimensional Gaussian distribution, it can be concluded that the probability is within 2 standard deviations from the mean value, and the result of about 99% was obtained within 2.58σ from the mean value. In previous work, by using 2.58σ z Approximate wake radius r zGood accuracy can be obtained, and this value is chosen as a balance value that can balance the prediction accuracy of the wake radius and wake depth.

[0042] A further derivation is then performed based on the assumption that the wake velocity at the wake boundary is approximately equal to the incident wind speed and using the mass flow conservation law for the selected control volume:

[0043]

[0044] Finally, the wind shear model is used to convert the wind speed difference into mass loss and the model is extended to three dimensions. The calculation formula for the additional mass loss △m of the incoming wind caused by the wind speed difference △u caused by wind shear is as follows:

[0045]

[0046] The calculation formula of the wind turbine wake model without wave action is as follows:

[0047]

[0048] In step S2, the platform position movement is converted into a transformation of three-dimensional coordinates. The specific process is as follows:

[0049] Onshore wind turbines do not change position over time. Although floating turbines are equipped with mooring systems for fixation, under the combined effects of wind and waves, the plane of the wind rotor will change its coordinates as the platform moves vertically, horizontally, and vertically. Assume that after a series of movements, the coordinates of the hub center at a certain moment are (x 0 ,y 0 ,z 0 ), the wake model should be rewritten as:

[0050]

[0051] Assume that at the initial position, the hub center and the platform center are on the same vertical line. Due to the influence of roll, pitch and yaw motion, the rotor plane and the vertical plane will form an angle. Assume that the platform center coordinates are (x', y', z') at this time, the angle between the rotor surface projected into the xoz plane and the vertical direction is θ 1 The angle between the projection of the wind wheel surface onto the yoz plane and the vertical direction is θ 2 , according to the coordinate transformation, the corresponding three-dimensional coordinates are:

[0052]

[0053] The wake model calculation formula is:

[0054]

[0055] In step S3, the deflection angle is converted into the wake offset to obtain the 3D-OFWT model, and the establishment process is as follows:

[0056] In the quasi-yaw wake model, the thrust on the quasi-yaw wind turbine is decomposed in the x and z directions, and the following is obtained:

[0057]

[0058] In the wind turbine control body, the sum of the momentum of the wind ahead of the wind turbine, the momentum lost by the impeller, and the momentum of the ambient wind entrained by the wake is equal to the wind momentum on the interface x=n on the wake; at the same time, the wind flow rate m in front of the wind turbine per unit time 1 Ambient wind flow rate with wake entrainment m 2 The sum is equal to the flow rate m on the interface x=n on the wake 3 . Applying the momentum conservation equation and mass conservation equation, we get:

[0059]

[0060] Assuming that the value of β is extremely small, then

[0061]

[0062] Combining various equations, we can get the center offset of the wake of the yaw-like wind turbine:

[0063]

[0064] Comprehensively speaking, the 3D-OFWT wake model of floating wind turbines under wind and wave action is expressed as follows:

[0065]

[0066] Among them, σ y =[k y (x-x'+z hub cosθ 2 sinθ 1 )+r 0 ] / 2.58; r z =k z (x-x'+z hub cosθ 2 sinθ 1 )+r 0 .

[0067] The 3D-OFWT wake model provided in this embodiment is compared with different wind tunnel measured data and other wake models to verify the accuracy of the wake model. The comparison results are as follows: Figure 3As shown in Figure 2, it can be seen that the prediction of the 3D-OFWT wake model fits the experimental data well. The velocity distribution characteristics of the wake region under different turbulence intensities were analyzed and compared, and the velocity law of the wake region was further clarified. The results are shown in Figure 2. Figure 4 shown.

[0068] In this embodiment, based on the preset Jensen wake model and the velocity distribution of the Gaussian function in the wake area, the mass conservation law is used for prediction, and a two-dimensional full wake model of the xz plane of the wake area under uniform inflow conditions is obtained; then, the additional mass loss of the incoming wind caused by the wind speed difference caused by the wind shear is considered to solve the three-dimensional wake distribution model; then, the position movement of the floating unit platform caused by the wave motion is converted into a three-dimensional coordinate transformation for further derivation; finally, through the yaw-like wake model, the thrust exerted on the wind turbine is decomposed in the x and z directions, and the momentum conservation equation and the mass conservation equation are applied to obtain the wake center offset, and finally the 3D-OFWT wake model of the floating wind turbine under the action of wind and waves is obtained.

[0069] Accurately and quickly mastering the wake characteristics of floating wind turbines is an inevitable requirement for improving the accuracy of existing wind farm capacity prediction, which has important guiding significance for the design process, safe operation and life improvement of large horizontal axis wind turbines.

[0070] The 3D-OFWT model provided in this embodiment can better predict the wake velocity distribution in different flow directions and radial positions, obtain the input information of the downstream flow field, and then improve the output power of the downstream wind turbine by changing the operation control strategy, optimize the production of offshore wind farms, improve the accuracy of capacity prediction of existing wind farms, reduce the fatigue load of wind turbine components, and increase the operating life of wind farms.

[0071] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for constructing a three-dimensional wake model of an offshore floating wind turbine, characterized in that Provide guidance for the wind power prediction and unit control operation strategy design of floating wind farms, improve wind turbine performance and increase energy output, including the following steps: S1. Add the wake Gaussian function distribution and vertical wind shear to build the wake model of the wind turbine without wave action, which is named the three-dimensional Jensen-Gaussian model. The calculation formula is: Among them, u ref is at the reference height z ref The wind speed of the incoming wind detected at the location; hub is the center height of the wind turbine hub; z+z hub is the height from the ground; α is the wind shear index; axial induction factor C T is the axial thrust coefficient; r0 is the initial wake radius; r z is the wake radius in the vertical direction; σ z is the standard deviation of the vertical Gaussian distribution; σ y is the standard deviation of the Gaussian distribution in the horizontal direction; S2. In the three-dimensional Jensen-Gaussian wake model, the position movement of the floating unit platform caused by wave motion is converted into a three-dimensional coordinate transformation. The transformed wake model is: C T is the axial thrust coefficient; u wave Represents the absolute speed of the wave; x0 = x'-z hub cosθ2sinθ1; y0=y'-z hub sinθ2;z0=z'+z hub cosθ2cosθ1; (x', y', z') are the coordinates of the center of the platform under the action of waves, θ1 is the angle between the projection of the wind rotor surface onto the xoz plane and the vertical direction, and θ2 is the angle between the projection of the wind rotor surface onto the yoz plane and the vertical direction; S3. On the basis of the improved yaw wake model, the deflection angle between the rotor plane and the vertical direction caused by wave motion is converted into a wake offset and added to the z direction of the three-dimensional transformed model to obtain the 3D-OFWT model of the floating wind turbine under the action of wind and waves. The model calculation formula is: Among them, p y =[k y (x-x'+z hub cosθ2sinθ1)+r0] / 2.58;r z =k z (x-x'+z hub cosθ2sinθ1)+r0.

2. The method for constructing a three-dimensional wake model of an offshore floating wind turbine according to claim 1, characterized in that: In step S3, based on the improved yaw wake model, the deflection angle between the wind rotor plane and the vertical direction caused by the wave motion is converted into a wake offset, and added to the z direction of the three-dimensional transformed model to obtain a 3D-OFWT model of a floating wind turbine under wind and wave action.

3. The method for constructing a three-dimensional wake model of an offshore floating wind turbine according to claim 1, characterized in that: In the fan control body, the sum of the wind momentum ahead of the fan, the momentum lost by the impeller and the ambient wind momentum absorbed by the wake is equal to the wind momentum at the x=n interface on the wake, and the momentum conservation equation and mass conservation equation are applied.

4. The method for constructing a three-dimensional wake model of an offshore floating wind turbine according to claim 1, characterized in that: The β value of the assumption is extremely small, and the calculation formula is as follows:

5. The method for constructing a three-dimensional wake model of an offshore floating wind turbine according to claim 1, characterized in that: The calculation formula for the offset of the fan wake center is as follows:

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