Method for calculating tip loss of floating wind turbine and application thereof

Abstract

The application provides a floating wind turbine tip loss calculation method and application, and belongs to the field of offshore wind turbine aerodynamics. In view of the technical limitations of the traditional tip loss correction method, which is not suitable for the multi-degree-of-freedom motion of the floating platform, leading to the dynamic change of the tip distance and the staggered wake, the method is based on the computational fluid dynamics method and the actuator line model to construct an accurate correction scheme. For the change of the tip distance caused by the surge and the pitch, the historical accumulated tip distance of the first blade behind the rotor is used to replace the traditional fixed tip distance. For the staggered wake phenomenon caused by the heave, the sway and the yaw, a floating wind turbine wake stagger correction formula is proposed. The application effectively makes up for the scene adaptation defects of the traditional correction method, significantly improves the simulation accuracy of the aerodynamic characteristics of the floating wind turbine, and provides reliable technical support for the wind turbine load prediction, control strategy optimization and deep sea engineering application.

Description

Technical Field

[0001] This invention belongs to the field of offshore wind power aerodynamics, and relates to a method for calculating tip loss of floating wind turbine blades and its application. Background Technology

[0002] Traditional tip loss correction models are all derived based on the aerodynamic characteristics of stationary wind turbines. Their core premise is that the turbine rotor maintains a fixed attitude, the wake field exhibits significant azimuth symmetry, and the vortex pitch of the wake vortex system is constant. However, the derivation process of these models fails to consider the combined effects of wind, waves, and current on floating wind turbines, which result in multi-degree-of-freedom motion. This directly breaks the azimuth symmetry assumption of the wake field, causing the wake vortex system to tilt and deform, and the vortex pitch to no longer be a fixed value. This fundamentally contradicts the core assumptions of traditional models and the actual flow state of floating wind turbines.

[0003] Because traditional tip loss correction formulas do not incorporate the influence of platform motion, the fixed vortex pitch parameters they employ cannot match the dynamic changes in the wake vortex pitch of floating wind turbines. Furthermore, they do not compensate for wake misalignment phenomena caused by heave, sway, and bow roll, leading to discrepancies between the calculated tip loss factor and the actual flow. These shortcomings limit the application of traditional correction methods in floating wind turbine scenarios, making it difficult to accurately reflect the true turbine load and hindering the safety and economic viability of deep-sea floating wind turbine engineering applications. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention proposes a method for calculating tip loss in floating wind turbines. This method, based on computational fluid dynamics, utilizes load calculations from an actuator model, the dynamic influence of multi-degree-of-freedom motion of the floating platform, a historical cumulative vortex pitch substitution correction strategy, and a wake misalignment correction factor to obtain a tip loss correction factor suitable for floating wind turbines. Applying this tip loss correction factor to the flow field simulation of a floating wind turbine platform can accurately simulate the aerodynamic characteristics of the floating wind turbine under the influence of platform motion and precisely quantify the impact of tip loss on the aerodynamic load of the wind turbine.

[0005] The first aspect of this invention provides a method for calculating tip loss of a floating wind turbine, comprising:

[0006] Correct the inflow angle in the tip loss correction factor and / or introduce a wake misalignment correction factor in the tip loss correction factor;

[0007] The inflow angle in the tip loss correction factor is corrected based on the historical cumulative vortex pitch of the first vortex blade behind the rotor;

[0008] The wake misalignment correction factor is obtained based on the one-to-one mapping relationship of the wake complex plane established by conformal mapping.

[0009] Furthermore, the inflow angle in the tip loss correction factor is corrected based on the historical cumulative vortex pitch of the first vortex vane behind the rotor as follows:

[0010]

[0011] in, The corrected equivalent inflow angle, The radius of the leaf at the leaf element unit. For the number of leaves, The historical cumulative vortex pitch of the leaf element unit; the leaf element unit constitutes the blade.

[0012] Furthermore, when the inflow angle in the tip loss correction factor is corrected and a wake misalignment correction factor is introduced into the tip loss correction factor, the expression for the tip loss correction factor after introducing the wake misalignment correction factor is:

[0013]

[0014] in, This is a correction factor for leaf tip loss. The wake stagger correction factor is calculated according to different stagger layouts as follows:

[0015] a. When the blade element unit is located within the projection of the first vortex vane behind the rotor:

[0016]

[0017] in, The distance by which the vortex line behind the rotor extends beyond the blade length;

[0018] b. When the position of the blade element unit exceeds the projection of the first vortex vane behind the rotor:

[0019]

[0020] in, This refers to the distance of the leaf element unit from the leaf tip, i.e. , This refers to the blade length.

[0021] Furthermore, the historical cumulative vortex pitch of the blade element unit is obtained in the following manner:

[0022] Calculate the instantaneous vortex pitch for each leaf element of each blade. :

[0023]

[0024] in, The radius of the leaf at this leaf element unit; The instantaneous inflow angle at the current moment. This refers to the number of leaves;

[0025] Calculate the instantaneous vortex pitch for each blade element at the current time step. Components in total vortex pitch :

[0026]

[0027] in, The time step for calculation, The rotational period of the rotor;

[0028] For each leaf element unit Integrating the data yields the historical cumulative vortex pitch for each blade element. :

[0029]

[0030] Furthermore, the expression for the tip loss correction factor, which incorporates the wake misalignment correction factor, is as follows: ,in As a correction factor for leaf tip loss, This refers to the wake misalignment correction factor; the wake misalignment correction factor is calculated according to different misalignment layouts as follows:

[0031] a. When the blade element unit that makes up the blade is located within the projection of the first vortex vane behind the rotor:

[0032]

[0033] in, The distance by which the vortex line behind the rotor extends beyond the blade length; The instantaneous vortex pitch of this leaf element unit;

[0034] b. When the position of the blade element unit that makes up the blade exceeds the projection of the first vortex vane behind the rotor:

[0035]

[0036] in, This refers to the distance of the leaf element unit from the leaf tip, i.e. , For the blade length, denoted as the leaf radius at the leaf element unit.

[0037] Furthermore, the leaf tip loss correction factor includes the Prandtl leaf tip loss correction factor or the shen leaf tip loss correction factor.

[0038] The second aspect of this invention provides an application of the tip loss correction factor obtained by the above-mentioned floating wind turbine tip loss calculation method in the flow field simulation of a floating wind turbine platform.

[0039] The beneficial effects of this invention are:

[0040] (1) Based on computational fluid dynamics and actuation line model, this invention addresses the failure of the fixed vortex pitch assumption and the problem of ignoring wake misalignment caused by neglecting the platform motion in traditional modified models by considering the dynamic influence of the multi-degree-of-freedom motion of the floating platform. This significantly improves the accuracy of simulation of aerodynamic load and wake field of floating wind turbine.

[0041] (2) The floating wind turbine tip loss correction factor of the present invention can be applied to a variety of existing fixed wind turbine correction methods, ensuring the comprehensiveness and adaptability of the correction method.

[0042] (3) This invention is applicable to different types of wind turbines and different blade characteristics; and it is applicable to the applied platform motion and the overall coupled motion of the floating wind turbine. Attached Figure Description

[0043] Figure 1 This is the calculation process for the tip loss correction method of floating wind turbines.

[0044] Figure 2 This is a schematic diagram of dynamic vortex pitch and vortex stagger.

[0045] Figure 3 This is a schematic diagram of a staggered layout (a).

[0046] Figure 4 This is a schematic diagram of staggered layout b.

[0047] Figure 5 This is a schematic diagram of the computational mesh of the actuation line model; where (a) is the side view section and (b) is the main view section.

[0048] Figure 6 This is a schematic diagram comparing the thrust of the modified method of the present invention with that of the traditional method; where (a), (b), and (c) represent motion amplitudes of 2m, 4m, and 6m, respectively.

[0049] Figure 7 This is a schematic diagram comparing the normal load and tangential load of the modified method of the present invention with those of the traditional method; where (a) is the normal load and (b) is the tangential load. Detailed Implementation

[0050] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The embodiments of the present invention are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0051] like Figure 1 As shown, the present invention provides a method for calculating tip loss of a floating wind turbine, including:

[0052] Correct the inflow angle in the tip loss correction factor and / or introduce a wake misalignment correction factor in the tip loss correction factor;

[0053] The inflow angle in the tip loss correction factor is corrected based on the historical cumulative vortex pitch of the first vortex blade behind the rotor;

[0054] The wake misalignment correction factor is obtained based on the one-to-one mapping relationship of the wake complex plane established by conformal mapping.

[0055] In a preferred embodiment, the leaf tip loss correction factor includes: Prandtl leaf tip loss correction factor or shen leaf tip loss correction factor, etc.

[0056] In a preferred embodiment, the method for calculating the tip loss of a floating wind turbine is to correct the inflow angle in the tip loss correction factor.

[0057] In this embodiment, the dynamic changes in vortex pitch caused by swaying and pitching motions are addressed, such as... Figure 2 As shown, where U represents the vortex pitch between different vortex plates. ∞ The incoming air velocity is used; the historical cumulative vortex pitch of the first vortex blade behind the rotor is used instead of the fixed vortex pitch of a traditional stationary fan, thereby quantifying the impact of platform motion on the vortex pitch, and the inflow angle of the tip loss correction factor is corrected based on the historical cumulative vortex pitch. The specific process is as follows:

[0058] For each blade element, the instantaneous inflow angle data is recorded within one rotation cycle, and the instantaneous vortex pitch of each blade element is calculated based on the instantaneous inflow angle. The calculation formula is as follows:

[0059]

[0060] in, This is the blade radius at that leaf element unit, which is the distance from the leaf element unit to the rotor rotation center. The instantaneous inflow angle at the current moment. This refers to the number of leaves;

[0061] Calculate the instantaneous vortex pitch for each blade element at the current time step. Components in total vortex pitch The calculation formula is as follows:

[0062]

[0063] in, The time step for calculation, The rotational period of the rotor;

[0064] For each leaf element unit Integrating the data yields the historical cumulative vortex pitch for each blade element. The calculation formula is as follows:

[0065]

[0066] Based on the historical cumulative vortex pitch of each leaf element unit Calculate the corresponding equivalent inflow angle. The corrected inflow angle, used as a correction factor for tip loss:

[0067]

[0068] In a preferred embodiment, the method for calculating the tip loss of a floating wind turbine is as follows: a wake misalignment correction factor is introduced into the tip loss correction factor.

[0069] In this embodiment, the wake misalignment phenomenon caused by heave, sway, and bow roll motions is addressed, such as... Figure 2 As shown, a wake misalignment correction factor specific to floating wind turbines is derived based on the complex plane mapping relationship, and the wake misalignment correction factor is introduced into the tip loss correction factor; the expression for the tip loss correction factor with the wake misalignment correction factor is: ,in This is a correction factor for leaf tip loss. The wake stagger correction factor is obtained through a one-to-one mapping relationship of the wake complex plane established by conformal mapping, and is calculated according to different stagger layouts as follows:

[0070] a. When the blade element unit is located within the projection of the first vortex vane behind the rotor, such as Figure 3 As shown, A is the current blade element, A' is its symmetrical point on the vortex plate, and B, E, and F are the projection points of the blade element on the vortex plate:

[0071]

[0072] in, This refers to the distance by which the vortex line behind the rotor extends beyond the blade length. The instantaneous vortex pitch of this leaf element unit;

[0073] b. When the position of the blade element unit exceeds the projection of the first vortex vane behind the rotor, such as Figure 4 As shown, A is the current blade element, A' is its symmetrical point on the vortex plate, and B, C, and D are the projection points of the blade element on the vortex plate:

[0074]

[0075] in, This refers to the distance of the leaf element unit from the leaf tip, i.e. , This refers to the blade length.

[0076] In a preferred embodiment, the method for calculating the tip loss of a floating wind turbine is as follows: the inflow angle in the tip loss correction factor is corrected, and a wake misalignment correction factor is introduced into the tip loss correction factor.

[0077] In this embodiment, considering the combined effects of vortex pitch variation and wake misalignment, the method for calculating the tip loss of the floating wind turbine is as follows:

[0078] First, the inflow angle in the tip loss correction factor is corrected based on the historical cumulative vortex pitch of the first vortex vane behind the rotor:

[0079]

[0080] in, This is the corrected equivalent inflow angle; The historical cumulative vortex pitch of the blade element unit is obtained in the following way:

[0081] Calculate the instantaneous vortex pitch for each leaf element of each blade. :

[0082]

[0083] Calculate the instantaneous vortex pitch for each blade element at the current time step. Components in total vortex pitch :

[0084]

[0085] For each leaf element unit Integrating the data yields the historical cumulative vortex pitch for each blade element. :

[0086]

[0087] Then, based on the tip loss correction factor for the corrected inflow angle, a wake misalignment correction factor is introduced, expressed as:

[0088]

[0089] in, This is a correction factor for leaf tip loss. The wake stagger correction factor is calculated according to different stagger layouts as follows:

[0090] a. When the blade element unit is located within the projection of the first vortex vane behind the rotor:

[0091]

[0092] in, The distance by which the vortex line behind the rotor extends beyond the blade length;

[0093] b. When the position of the blade element unit exceeds the projection of the first vortex vane behind the rotor:

[0094]

[0095] in, This refers to the distance of the leaf element unit from the leaf tip, i.e. .

[0096] In this embodiment, when the leaf tip loss correction factor This is the Prandtl tip loss correction factor, i.e. The corrected tip loss correction factor for:

[0097]

[0098] Taking the NREL 5MW floating wind turbine as an example, the tip loss obtained based on the above method is established as follows: Figure 5 The simulation model of the flow field of the floating wind turbine platform based on the actuation line model is shown. The calculation condition is a uniform wind speed of 11.4 m / s. The platform motion is taken as swaying motion, with a motion period of 10 s and amplitudes of 2 m, 4 m, and 8 m. The specific simulation process is as follows:

[0099] S1. The rotating blades of the floating wind turbine are simplified into virtual actuation lines that bear aerodynamic loads, and the virtual actuation lines are discretized into several blade element units along the radial direction of the blades.

[0100] S2. Considering the multi-degree-of-freedom motion of the floating platform, analyze the influence of each motion on the relative velocity of the blades, and calculate the aerodynamic load of the blade element unit under the influence of the floating platform motion.

[0101] S3. The blade element unit aerodynamic load is corrected and calculated by using the blade tip loss correction factor obtained by correcting the inflow angle in the blade tip loss correction factor as described above, and the corrected blade element unit aerodynamic load is obtained.

[0102] S4. Convert the modified blade element aerodynamic load into a three-dimensional volume force and add it as a source term to the computational fluid dynamics control equation to realize the projection of the aerodynamic load in the flow field and complete the flow field simulation after the blade tip loss is corrected at the current time step.

[0103] In one embodiment, the specific process of calculating the aerodynamic load of the blade element unit under the influence of the floating wind turbine platform's motion in step S2 is as follows:

[0104] S2.1, The additional velocity of the blades caused by the platform motion With free flow velocity Blade rotational tangential velocity By combining these measurements, the total relative velocity at the leaf element unit can be obtained. The calculation formula is as follows:

[0105]

[0106] Based on the obtained total relative velocity Based on the airfoil lift-drag coefficient and blade element geometry parameters (chord length, installation angle), the lift on the blade element unit is calculated. and resistance :

[0107]

[0108]

[0109] in, Let c represent the fluid density, c represent the chord length, and dr represent the length of this airfoil element on the blade. and These are the lift coefficient and drag coefficient for the corresponding airfoil;

[0110] S2.2 Lift of the leaf element unit based on S2.1 and resistance Lift force on all leaf element units and resistance The total aerodynamic thrust and torque of the entire fan are obtained by accumulating the integrals.

[0111] In one embodiment, step S3 uses a modified tip loss correction factor. The aerodynamic loads of the blade element unit are corrected and calculated as follows:

[0112]

[0113]

[0114] in, , These represent the lift and drag of the modified leaf element unit, respectively.

[0115] In one embodiment, the projection method of the corrected blade element aerodynamic load in step S4 is as follows:

[0116] For each blade element, a three-dimensional Gaussian function smoothing process is used to transform the aerodynamic load of the discrete blade element into a continuously distributed volume force. The calculation formula is as follows:

[0117]

[0118] in, For Gaussian projection kernel, For the projection kernel size, The distance from the calculated grid point position to the first The distance between leaf element units, This represents the total number of leaf element units. The aerodynamic load vector on the blade element is obtained according to formulas (17) and (18).

[0119] This invention, based on the aerodynamics theory of wind turbines, proposes a tip loss correction method applicable to floating wind turbines. A comparison of the calculation results before and after correction is provided below. Figures 6-7 As shown, the black line represents the calculation results of tip loss correction for stationary fans used in existing aerodynamic theories, while the red curve represents the calculation results using the correction. The results show that the correction effect is significant for the specific implementation example. After adopting the correction method proposed in this invention, the amplitude of blade aerodynamic load fluctuation is significantly improved. Under the influence of small-amplitude platform motion, whether or not tip loss correction for floating fans is used has little impact on the calculation results. However, when the platform motion amplitude is large, whether or not tip loss correction for floating fans is used has a significant impact on the blade load calculation results. Therefore, for the aerodynamic load calculation of floating fans, tip loss correction for floating fans that considers platform motion should be used under the influence of large-amplitude platform motion.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for calculating tip loss of a floating wind turbine, characterized in that, include: Correct the inflow angle in the tip loss correction factor and / or introduce a wake misalignment correction factor in the tip loss correction factor; The inflow angle in the blade tip loss correction factor is corrected based on the historical cumulative vortex pitch of the first vortex blade behind the rotor; specifically as follows: in, The corrected equivalent inflow angle, The radius of the leaf at the leaf element unit. For the number of leaves, The historical cumulative vortex pitch of the leaf element unit; the leaf element unit constitutes the blade; The wake misalignment correction factor is obtained based on the one-to-one mapping relationship of the wake complex plane established by conformal mapping; the expression for the tip loss correction factor that incorporates the wake misalignment correction factor is: ,in As a correction factor for leaf tip loss, This refers to the wake misalignment correction factor; the wake misalignment correction factor is calculated according to different misalignment layouts as follows: a. When the blade element unit that makes up the blade is located within the projection of the first vortex vane behind the rotor: in, This refers to the distance by which the vortex line behind the rotor extends beyond the blade length; when only the tip loss correction factor is introduced into the wake misalignment correction factor... This represents the instantaneous vortex pitch of the blade element; when the inflow angle in the tip loss correction factor is corrected simultaneously, and a wake misalignment correction factor is introduced into the tip loss correction factor... Historical cumulative vortex pitch of leaf element unit ; b. When the position of the blade element unit that makes up the blade exceeds the projection of the first vortex vane behind the rotor: in, This refers to the distance of the leaf element unit from the leaf tip, i.e. , The blade length; The historical cumulative vortex pitch of the blade element unit is obtained in the following way: Calculate the instantaneous vortex pitch for each leaf element of each blade. : in, The radius of the leaf at this leaf element unit; The instantaneous inflow angle at the current moment. This refers to the number of leaves; Calculate the instantaneous vortex pitch for each blade element at the current time step. Components in total vortex pitch : in, The time step for calculation, The rotational period of the rotor; For each leaf element unit Integrating the data yields the historical cumulative vortex pitch for each blade element. : (6)。 2. The method for calculating tip loss of a floating wind turbine according to claim 1, characterized in that, The leaf tip loss correction factor includes the Prandtl leaf tip loss correction factor or the shen leaf tip loss correction factor.

3. The application of the tip loss correction factor obtained by the floating wind turbine tip loss calculation method according to claim 1 or 2 in the flow field simulation of the floating wind turbine platform.

Images