Wind turbine generator blade aerodynamic performance simulation calculation method based on fluid-structure interaction and overlapping grids

Abstract

The invention relates to a wind turbine generator blade aerodynamic performance simulation calculation method based on fluid-structure interaction and overlapping grids, which comprises the steps of data collection, coordinate transformation, blade modeling, flow field calculation domain establishment, grid division, turbulence model setting, overlapping grid setting, coupling interface selection, equation solving and the like. The structure dynamic state of the blade under the action of airflow is accurately captured, the complex motion working condition of rotation of the blade is ingeniously and flexibly processed through the overlapping grid technology, and the actual operation state of a wind turbine generator is fitted in an omnibearing mode. According to the method, the number of tests can be reduced as much as possible in the design stage, blade design accuracy and reliability are improved, research and development cost is reduced, and research and development time is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of aerodynamic simulation of wind turbine blades, and in particular to a method for simulating and calculating aerodynamic performance of wind turbine blades based on fluid-solid coupling and overlapping grids, which is used to implement aerodynamic simulation calculation of wind turbine blades. Background Art

[0002] In recent years, wind power generation has been widely used due to its advantages of clean energy and renewable energy. Its essence is to convert wind energy into mechanical energy, and then convert mechanical energy into electrical energy. As the core component of wind power generation equipment, wind turbine blades will directly affect the performance and life of the wind turbine, including power output, noise level, vibration and fatigue life. At present, the research on the optimization design of wind turbine blades mainly focuses on experimental methods and numerical simulation methods. Due to the large size and high cost of wind turbines, wind tunnel experiments are generally used to measure the aerodynamic characteristics of blades. In addition, wind turbines can also be installed on site for testing to measure the actual output power and response curve. With the continuous development of computer technology, numerical simulation has been widely used in various engineering fields, but most of them use simplified models, which makes it difficult to fully and accurately reproduce the detailed information of the complex flow field around the wind turbine blades, such as fine turbulent structure, boundary layer separation details and dynamic evolution characteristics of the wake field. Therefore, three-dimensional numerical simulation calculation of the aerodynamic performance of wind turbine blades is of great significance for the evaluation of blade aerodynamic performance. Summary of the invention

[0003] In view of the above situation, in order to overcome the deficiencies of the prior art, the purpose of the present invention is to propose a method for simulating and calculating the aerodynamic performance of wind turbine blades based on fluid-solid coupling and overlapping grids, so as to realize aerodynamic simulation calculation of wind turbines.

[0004] The technical solution provided by the present invention is:

[0005] A method for simulating and calculating the aerodynamic performance of a wind turbine blade based on fluid-structure coupling and overlapping grids comprises the following steps:

[0006] S1. Data collection: Obtain basic parameters of wind turbine and blade structural parameters according to the wind turbine design manual. Basic parameters of wind turbine include rated power, number of blades, wind rotor, hub diameter, cut-in wind speed, rated wind speed, cut-out wind speed, cut-in speed, rated speed, and cone angle; blade structural parameters include blade length, blade root diameter, blade chord length, blade twist angle, and airfoil profile.

[0007] S2. Coordinate transformation and blade modeling: The two-dimensional airfoil coordinates (x0, y0) in the airfoil profile are transformed into coordinate values ​​(x1, y1) with the aerodynamic center (a, b) as the origin, and then the two-dimensional coordinates of the discrete points are further transformed into three-dimensional space coordinates (x2, y2, z), and a three-dimensional blade model is established by curve group layering:

[0008] (x1, y1) = (x0, y0) - (a, b)

[0009]

[0010] z=r

[0011] Where β is the blade twist angle, r is the layer radius;

[0012] S3. Establish the flow field calculation domain: The calculation domain is divided into two parts: fluid domain and solid domain. The solid domain is the wind turbine. The fluid domain is divided into two parts: background domain and foreground domain. The background domain is a cylindrical domain with a diameter of 5D and 10D in front of the wind turbine and a diameter of 5D. The foreground fluid domain is a disk with a diameter of 1.2D and a thickness of 0.15D. The boundary between the two domains is the overlapping interface. D is the diameter of the wind turbine impeller.

[0013] S4. Meshing: Use tetrahedral meshes with better adaptability to mesh the fluid domain and solid domain respectively, and locally encrypt the mesh near the wall of the fan blade to verify mesh independence and numerical stability;

[0014] S5. Turbulence model setting: The SST k-ω turbulence model is used to solve the turbulent motion of the fluid in the fluid domain. This model not only corrects the propagation of turbulent shear stress to make it more suitable for predicting the separation flow under adverse pressure gradient, but also considers the influence of orthogonal divergence terms. The specific turbulence model is:

[0015]

[0016] Among them, G k and G ω is the generated term caused by the existence of velocity gradient; Γ k and Γ ω is the effective diffusion term; Y k He HeY ω is the dissipation term caused by turbulent motion; D ω is the cross diffusion term;

[0017] S6, Overlapping grid setting: Overlapping grid model is used to analyze the interaction between fluid and solid and the rotation of blades; Overlapping grid allows each grid subdomain to be nested, overlapped, and covered, and flow field information is transferred between grids through interpolation. Compared with traditional structured grids, overlapping grids have the advantages of small spatial coupling and strong adaptability;

[0018] The main calculation steps of overlapping grids are as follows: (1) Digging holes: Eliminate redundant overlapping cells inside the object and outside the calculation area to simplify the calculation. (2) Establish regional connectivity: Find the best grid that can transmit information near the receptor unit as the donor unit. (3) Interpolation calculation: After completing the search and matching of the receptor unit, the boundary exchange method (BEM) is used to establish data transmission and exchange between the boundary points and the receptor units.

[0019] S7: Coupling interface selection: Set the outer surface of the fan blade as the fluid-solid coupling interface. The background flow inlet is the velocity inlet, and the outlet pressure is set to the pressure outlet;

[0020] S8: Solve equations: Solve the Reynolds time-averaged NS equations and mass conservation equations through the finite volume method to analyze the motion information of the fluid in the fluid domain. The continuity equation and momentum equation of the incompressible fluid are:

[0021]

[0022] In the formula, u, ρ, and p are the velocity, density, and pressure of the fluid, respectively;

[0023] S9: Convergence determination: Set the residual convergence standard to 1e-6, and determine whether the residual converges at the current moment. If not, jump to step S8 and continue iterative solution. If converged, it is determined that the calculation is completed at the current moment, and the pressure information on the blade surface is transmitted to the dynamic load solver in real time through the system coupler;

[0024] S10: Dynamic structural solver: Add fixed constraints to the fan base and rotation constraints to the impeller. The external load of the fan impeller is applied by the fluid-solid coupling interface. The finite element method is used to calculate the motion and position information of the blades. The position information of the blades is transmitted to the flow solver in real time through the bidirectional coupler, and the position and motion state at the next moment are determined based on the external torque on the impeller.

[0025] S11: Time step update: Determine whether the residual of the system coupling calculation at the current moment has converged. If the residual has not converged, continue the iterative calculation; if the residual has converged, enter the next moment iterative calculation and output the calculation result.

[0026] In the face of the difficulty of traditional simplified numerical models to fully and accurately reproduce the detailed information of the complex flow field around the wind turbine blades, such as fine turbulence structure, boundary layer separation details, and dynamic evolution characteristics of the wake field, the wind turbine blade aerodynamic performance simulation calculation method based on fluid-structure coupling and overlapping grids relies on the fluid-structure coupling algorithm to accurately capture the structural dynamics of the blades under the action of airflow, and uses overlapping grid technology to cleverly and flexibly handle the complex motion conditions of blade rotation, fully fitting the actual operating status of the wind turbine. This method can minimize the number of tests in the design stage, improve the accuracy and reliability of blade design, reduce R&D costs, and shorten R&D time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic flow chart of a method for simulating and calculating the aerodynamic performance of a wind turbine blade based on fluid-structure coupling and overlapping grids provided in an embodiment of the present invention.

[0028] Figure 2 A three-dimensional model diagram of a wind turbine provided in an embodiment of the present invention.

[0029] Figure 3 This is an example diagram of a computational domain provided in an embodiment of the present invention.

[0030] Figure 4 This is an example diagram of grid division provided by an embodiment of the present invention.

[0031] Figure 5 The blade velocity distribution cloud diagram under different working conditions provided by the embodiment of the present invention.

[0032] Figure 6 The blade pressure distribution cloud diagram under different working conditions provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0034] See also Figure 1 A method for simulating and calculating the aerodynamic performance of a wind turbine blade based on fluid-structure coupling and overlapping grids in this embodiment includes the following steps:

[0035] S1. Data collection: Obtain basic parameters of wind turbine and blade structure parameters according to the wind turbine design manual. Basic parameters of wind turbine include rated power, number of blades, wind rotor, hub diameter, cut-in wind speed, rated wind speed, cut-out wind speed, cut-in speed, rated speed, extension, shaft inclination angle, and cone angle; blade structure parameters include blade length, blade root diameter, blade chord length, blade twist angle, and airfoil profile. Taking a 2.5MW wind turbine in a wind farm as an example, the basic parameters of the wind turbine are shown in the following table.

[0036] Table 1 Basic parameters of fan

[0037]

[0038] S2. Coordinate transformation and blade modeling: The two-dimensional airfoil coordinates (x0, y0) in the airfoil profile are transformed into coordinate values ​​(x1, y1) with the aerodynamic center (a, b) as the origin, and then the two-dimensional coordinates of the discrete points are further transformed into three-dimensional space coordinates (x2, y2, z).

[0039] (x1, y1) = (x0, y0) - (a, b)

[0040]

[0041] z=r

[0042] Where β is the blade twist angle and r is the layer radius.

[0043] Taking an airfoil section with a layer radius r of 14 as an example, some actual coordinates obtained after coordinate transformation are shown in the following table.

[0044] Table 2 Coordinate change table

[0045] <![CDATA[x2]]> <![CDATA[y2]]> <![CDATA[x2]]> <![CDATA[y2]]> <![CDATA[x2]]> <![CDATA[y2]]> <![CDATA[x2]]> <![CDATA[y2]]> 11.96 2.46 11.41 2.50 10.61 2.55 9.77 2.58 8.82 2.63 7.77 2.66 6.65 2.69 5.54 2.70 4.44 2.69 3.34 2.64 2.25 2.54 1.18 2.38 0.13 2.11 -0.89 1.75 -1.68 1.38 -2.42 0.97 -3.01 0.55 -3.46 0.16 -3.78 -0.19 -3.96 -0.50 -3.99 -0.81 -3.83 -1.13 -3.54 -1.38 -3.11 -1.60 -2.54 -1.79 -1.83 -1.92 -0.99 -1.99 -0.03 -1.96 1.03 -1.82 3.13 -1.21 5.14 -0.24 6.13 0.34 7.12 0.93 9.07 1.90 10.73 2.32 11.43 2.38

[0046] According to the airfoil coordinates at different layer radii, a three-dimensional blade model is established by curve group layer laying method ( Figure 2 ).

[0047] S3. Establish the flow field calculation domain: The calculation domain is divided into two parts: the fluid domain and the solid domain. The solid domain is the wind turbine. The fluid domain is divided into two parts: the background domain and the foreground domain. The background domain is a cylindrical domain with a diameter of 5D and 10D in front of the wind turbine and a diameter of 5D; the foreground fluid domain is a disk with a diameter of 1.2D and a thickness of 0.15D. The boundary between the two domains is the overlapping interface. In this embodiment, D = 121m.

[0048] S4. Meshing: Use tetrahedral meshes with better adaptability to mesh the fluid domain and solid domain respectively, and locally encrypt the mesh near the wall of the fan blade ( Figure 4 ).

[0049] S5. Turbulence model setting: The SST k-ω turbulence model is used to solve the turbulent motion of the fluid in the fluid domain. This model not only corrects the propagation of turbulent shear stress to make it more suitable for predicting the separated flow under adverse pressure gradient, but also considers the influence of orthogonal divergence terms.

[0050]

[0051] Among them, G k and G ωis the generated term caused by the existence of velocity gradient; Γ k and Γ ω is the effective diffusion term; Y k He HeY ω is the dissipation term caused by turbulent motion; D ω is the cross diffusion term.

[0052] S6. Overlapping grid setting: Overlapping grid model is used to analyze the interaction between fluid and solid and the rotation of blades. Overlapping grid allows each grid subdomain to be nested, overlapped, and covered, and flow field information is transferred between grids through interpolation. Compared with traditional structured grids, overlapping grids have the advantages of small spatial coupling and strong adaptability.

[0053] The main calculation steps of overlapping grids are as follows: (1) Digging holes: Eliminate redundant overlapping cells inside the object and outside the calculation area to simplify the calculation. (2) Establish regional connectivity: Find the best grid that can transmit information near the receptor unit as the donor unit. (3) Interpolation calculation: After completing the search and matching of the receptor unit, the boundary exchange method (BEM) is used to establish data transmission and exchange between the boundary points and the receptor units.

[0054] S7: Coupling interface selection: Set the outer surface of the fan blade as the fluid-solid coupling interface. The background flow inlet is the velocity inlet, and the outlet pressure is set to the pressure outlet.

[0055] S8: Solve equations: Solve the Reynolds time-averaged NS equations and mass conservation equations through the finite volume method to analyze the motion information of the fluid in the fluid domain. The continuity equation and momentum equation of the incompressible fluid are:

[0056]

[0057] Where u, ρ, and p are the velocity, density, and pressure of the fluid, respectively.

[0058] S9: Convergence determination: Set the residual convergence standard to 1e-6 to determine whether the residual converges at the current moment. If not, jump to step S8 and continue iterative solution. If converged, it is determined that the calculation is completed at the current moment, and the pressure information on the blade surface is transmitted to the dynamic structure solver in real time through the system coupler.

[0059] S10: Dynamic structural solver: Add fixed constraints to the fan base and rotation constraints to the impeller. The external load of the fan impeller is applied by the fluid-solid coupling interface. The finite element method is used to calculate the motion and position information of the blades. The position information of the blades is transmitted to the flow solver in real time through the bidirectional coupler, and the position and motion state at the next moment are determined based on the external torque on the impeller.

[0060] S11: Time step update: Determine whether the residual of the system coupling calculation at the current moment has converged. If the residual has not converged, continue the iterative calculation; if the residual has converged, enter the next moment iterative calculation and output the calculation result. The time step is 0.01s. The blade velocity distribution and pressure distribution under different working conditions are as follows Figure 5 , Figure 6 shown.

Claims

1. A method for simulating and calculating the aerodynamic performance of wind turbine blades based on fluid-structure coupling and overlapping grids, characterized in that: The following steps are involved: S1. Obtain basic parameters of the wind turbine and blade structural parameters according to the wind turbine design manual, where the basic parameters of the wind turbine include rated power, number of blades, wind rotor, hub diameter, cut-in wind speed, rated wind speed, cut-out wind speed, cut-in speed, rated speed, and cone angle; the blade structural parameters include: blade length, blade root diameter, blade chord length, blade torsion angle, and airfoil profile; S2, coordinate transformation and blade modeling: transform the two-dimensional airfoil coordinates in the airfoil profile into coordinate values ​​with the aerodynamic center as the origin, and then further transform the two-dimensional coordinates of the discrete points into three-dimensional space coordinates, and establish a three-dimensional blade model by curve group layering; S3. Establish the flow field calculation domain: the calculation domain is divided into two parts: fluid domain and solid domain. The solid domain is the wind turbine, and the fluid domain is divided into two parts: background domain and foreground domain. The background domain is a cylindrical domain with a diameter of 5D and 10D in front of the wind turbine and a diameter of 5D; the foreground fluid domain is a disk with a diameter of 1.2D and a thickness of 0.15D. The boundary between the two domains is the overlapping interface, and D is the diameter of the wind turbine impeller. S4, grid division; S5, turbulence model setting: use the SST k-ω turbulence model to solve the turbulent motion of the fluid in the fluid domain; S6, Overlapping grid setting: The overlapping grid model is used to analyze the interaction between fluid and solid and the rotational motion of the blade. The overlapping grid allows each grid subdomain to be nested, overlapped, and covered, and the flow field information is transferred between grids through interpolation; S7, coupling interface selection: set the outer surface of the fan blade as the fluid-solid coupling interface, the background flow inlet as the velocity inlet, and the outlet pressure as the pressure outlet; S8, Flow field calculation: Solve the Reynolds time-averaged NS equations and mass conservation equations through the finite volume method to analyze the fluid motion information in the fluid domain; S9, convergence determination: Set the residual convergence standard to 1e-6, determine whether the residual converges at the current moment, if not, jump to step S8, and continue iterative solution; if converged, determine that the calculation is completed at the current moment, and transmit the pressure information on the blade surface to the dynamic load solver in real time through the system coupler; S10: Dynamic structural solver: Add fixed constraints to the fan base and rotation constraints to the impeller; the external load of the fan impeller is applied by the fluid-solid coupling interface; the finite element method is used to calculate the motion and position information of the blades; the position information of the blades is transmitted to the flow solver in real time through the bidirectional coupler, and the position and motion state at the next moment are determined based on the external torque on the impeller; S11: Time step update: Determine whether the residual of the system coupling calculation at the current moment has converged. If the residual has not converged, continue the iterative calculation; if the residual has converged, enter the next moment iterative calculation and output the calculation result.

2. The method for simulating and calculating the aerodynamic performance of wind turbine blades based on fluid-structure coupling and overlapping grids according to claim 1 is characterized in that: The specific method of the coordinate transformation and blade modeling in step S2 is: The two-dimensional airfoil coordinates (x0, y0) in the airfoil profile are transformed into coordinate values ​​(x1, y1) with the aerodynamic center (a, b) as the origin, and then the two-dimensional coordinates of the discrete points are further transformed into three-dimensional space coordinates (x2, y2, z), and a three-dimensional blade model is established by curve group layering. (x1, y1) = (x0, y0) - (a, b) z＝r Where β is the blade twist angle and r is the layer radius.

3. The aerodynamic performance simulation calculation method of wind turbine blades based on fluid-structure coupling and overlapping grids according to claim 1 is characterized in that: The meshing method of step S4 is: using a tetrahedral mesh with better adaptability to mesh the fluid domain and the solid domain respectively, and locally encrypting the mesh near the wall surface and the trailing edge of the fan blade.

4. The aerodynamic performance simulation calculation method of wind turbine blades based on fluid-structure coupling and overlapping grids according to claim 1 is characterized in that: The turbulence model of step S5 is specifically: Among them, G k and G ω is the generated term caused by the existence of velocity gradient; Γ k and Γ ω is the effective diffusion term; Y k He HeY ω is the dissipation term caused by turbulent motion; D ω is the cross diffusion term.

5. The method for simulating and calculating the aerodynamic performance of wind turbine blades based on fluid-structure coupling and overlapping grids according to claim 1 is characterized in that: The Reynolds time-averaged NS equation and mass conservation equation of the flow solver in step S8 are specifically: Where u, ρ, and p are the velocity, density, and pressure of the fluid, respectively.

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