Simulation calculation method for simulating surface damage characteristics of fan blade under lightning arc sweeping

Abstract

The invention discloses a simulation calculation method for simulating the surface damage characteristics of a fan blade under lightning arc sweeping, and the method comprises the steps: building a full-size model of a non-conductive surface fan blade with a lightning arrester in a typical region, and building an arc development simulation calculation model of the fan blade under the lightning arc sweeping effect; obtaining surface physical parameters of the fan blade; further establishing a current conduction simulation calculation model of each region of the fan blade to obtain current shunting characteristics of each region; and finally, establishing an electric-thermal-mechanical coupling simulation calculation model of each area part of the fan blade, obtaining the damage characteristics of the fan blade, and realizing simulation calculation of the arc sweeping damage characteristics of the full-size fan blade. The electric arc development process, current distribution and damage characteristics of the fan blade under the lightning electric arc sweeping effect in the movement process are obtained by changing the position of the electrode, the test cost is saved, the research process of the lightning protection design of the fan blade is accelerated, and a research basis is provided for lightning damage and protection design of all areas of the fan blade.

Description

Technical Field

[0001] The invention belongs to the technical field of lightning damage testing and protection of wind turbine blades, and in particular relates to a simulation calculation method for simulating surface damage characteristics of wind turbine blades under the sweep of a lightning arc. Background Art

[0002] As the global demand for clean energy continues to grow, wind energy has been widely used and developed rapidly around the world. As a key component of wind turbines, blades are at high risk of being struck by lightning. The installed capacity of my country's wind power generation system continues to increase. The 18-megawatt offshore wind turbines independently developed have a wind rotor diameter of 260 meters. As the diameter increases, the probability of lightning strikes increases exponentially, and the difficulty and cost of protection increase exponentially.

[0003] When a wind turbine blade is struck by lightning, the lightning current will be conducted inside the blade. Wind turbine blades are mostly made of glass fiber composite materials. This material cannot conduct and disperse the lightning current under the action of lightning current. The current accumulates locally, causing the material to be damaged by burning, ablation, delamination, cracking, etc. The lightning damage to the wind turbine blades affects its performance and may even cause the wind turbine system to shut down and the entire machine to burn out. The lightning damage rate in Yunnan, Guizhou and other places in my country is as high as 9.8 times / (100 units / year). The average maintenance cost of each wind turbine blade is more than 150,000 yuan, and severely damaged blades need to be replaced with new ones, causing serious economic losses.

[0004] According to the GBT33629-2017 standard, the full-size blade movement method is used to simulate the blade damage experiment under the swept arc, and the lightning current conduction and damage characteristics of various parts of the blade are analyzed. However, this experiment is difficult, and the design of the mobile experimental device, including speed, load-bearing, height, etc., is costly and difficult. There is no relevant experimental research and exploration at present, but the implementation of this swept conduction test is the premise of subsequent lightning damage research in various regions, and it is also the basis for the lightning protection design of wind turbine blades. Therefore, it is necessary to study the damage influence characteristics of various areas on the surface of the wind turbine blade under the lightning arc sweep of the wind turbine blade. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a simulation calculation method for simulating the surface damage characteristics of wind blades under the sweep of lightning arc, to realize the simulation calculation of the arc sweep damage characteristics of full-size wind blades, and further obtain the arc development process, current distribution and damage characteristics of the wind blades under the sweep of lightning arc during movement by changing the electrode position, thereby saving test costs, accelerating the research progress of lightning protection design of wind blades, and providing a research basis for lightning damage and protection design of various areas of wind blades.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A simulation calculation method for simulating the surface damage characteristics of a wind turbine blade under the sweep of a lightning arc comprises the following steps:

[0008] Step 1: Establish a full-scale model of a non-conductive surface wind turbine blade with a lightning receptor in a typical area, and determine the lightning waveform parameters and wind turbine blade material parameters;

[0009] Step 2: Place multiple electrodes at different positions of the blades and at a distance of ≥50 mm from the blades to establish a simulation calculation model for arc development of the wind turbine blades under the sweeping action of lightning arcs, and obtain physical parameters of the surface of the wind turbine blades;

[0010] Step 3, based on the arc development simulation model of the full-size fan blade in step 2, a current conduction simulation calculation model of each region of the fan blade is established to obtain the current shunt characteristics of each region;

[0011] Step 4, establishing an electric-thermal-mechanical coupling simulation calculation model for each area of ​​the fan blade to obtain the damage characteristics of the fan blade;

[0012] Step 5, by injecting lightning waveforms at different electrode positions to simulate the movement process of the wind turbine blades under the sweeping action of the lightning arc, and then simulating the development law of the arc action in each area of ​​the wind turbine blades under the action of the sweeping arc, the arc development process, current distribution and damage characteristics of the wind turbine blades under the sweeping action of the lightning arc during the movement are obtained.

[0013] Preferably, the multiple electrodes described in step 2 are all connected to arc-starting wires, and a lightning channel is established through the arc-starting wires.

[0014] Preferably, the calculation process of the arc development simulation calculation model described in step 2 includes: calculation of a current module, a laminar flow module, a heat transfer module, and a heat transfer module between the arc and the contact surface between the anode and cathode;

[0015] Extract the physical parameters of the wind turbine blade surface in the arc of the lightning arrester and the nearby area on the arc extension path at the electrode position calculated by the arc development simulation model;

[0016] The physical parameters of the fan blade surface include current density, heat flux density and temperature distribution parameters.

[0017] Furthermore, the current module uses Maxwell's equations to model the electromagnetic field and obtain the current density parameters. The calculation equation is shown as follows:

[0018]

[0019] In the formula, is the magnetic field intensity vector, σ is the conductivity, is the electric field strength, is the magnetic flux density, μ0 is the magnetic permeability, is the electric displacement vector, ε is the dielectric constant, V is the electric potential, is the magnetic potential, is the current density, μ is the viscosity coefficient;

[0020] The laminar flow module uses the classical conservation equation to describe the flow phenomenon of magnetic fluid. The calculation equation is shown as follows:

[0021]

[0022] Equation (2) is the mass conservation equation in the fluid domain, and (3) is the momentum conservation equation. is the velocity vector, ρ is the density, p is the pressure, and I is the identity matrix;

[0023] Heat transfer module Arc heat flux Q, Joule heat Q J , external radiation energy loss Q rad Calculated by the energy conservation equation, the calculation equation is as follows:

[0024]

[0025] In the formula, C p is the specific heat at constant pressure, T is the temperature, k is the thermal conductivity, k B is the Boltzmann constant, e is the charge of the electron, ε N is the plasma radiation coefficient;

[0026] The heat exchange equation for heat transfer between the arc and the contact surface of the anode and cathode is shown as follows:

[0027]

[0028] In the formula, q anode is the anode heat, q cathode is the cathode heat, q is the heat flow vector; n is the normal vector; J is the current density; φ a is the work function of the anode material; φ c is the cathode material work function; k B is the Boltzmann constant; V i is the air ionization energy; j i is the ion current; j e is the electron current.

[0029] Preferably, in the current conduction simulation calculation model of each area of ​​the fan blade described in step 3, the lightning current satisfies Ampere's law and the current conservation equation during the conduction process of the full-size fan blade, and the calculation equation is shown as follows:

[0030]

[0031] Where: is the current density of the external current source, is the unit current density, V is the electric potential, ε0 is the vacuum dielectric constant, ε r is the relative dielectric constant, μ0 is the vacuum magnetic permeability, μ r is the relative magnetic permeability, is the magnetic vector, For speed.

[0032] Preferably, the electrical-thermal-mechanical coupling simulation calculation process described in step 4 includes: electric field, heat conduction and thermal expansion stress distribution states.

[0033] Furthermore, when the lightning current acts on the sample, the electric field obeys Maxwell's charge conservation equation, and the finite element control equation of the electric field is as follows:

[0034]

[0035] Where V is the unit volume; S is the unit cross-sectional area, r c is the unit charge density, n is the external normal of surface S, E is the electric field intensity, σ E is the conductivity matrix; is the cell volume current density; is the electric potential;

[0036] The Joule heat energy power of the current is:

[0037]

[0038] When a transient current flows, its energy formula is as follows:

[0039]

[0040] Where, t is time;

[0041] According to its conversion efficiency, the thermal energy formula is:

[0042] Q ce =ηP ce (10)

[0043] Where η is the conversion efficiency.

[0044] Furthermore, the heat balance equation of the material heat conduction process during the lightning strike is shown as follows:

[0045] Q ce =Q c +Q d +Q f +Q s (11)

[0046] In the formula, Q c is the heat conduction energy, Q dis the thermal convection energy, Q f is the thermal radiation energy, Q s is the ablation heat energy.

[0047] From the steady-state Fourier heat conduction equation, we can get:

[0048]

[0049] Where ρ is density, U is internal energy, r is the heat generated in the volume, δ is the potential change function, and θ is the temperature change function.

[0050] Furthermore, the thermal expansion stress distribution state of the local material during the simulation is obtained based on the thermal expansion equation and the basic equation of elastic mechanics. The calculation equation is shown as follows:

[0051]

[0052] Where b x 、b y 、b z They are the components of the volume force on the object material in the x, y, and z directions, and the strain force components are σ xx , σ xy and σ xz .

[0053] Compared with the prior art, the present invention has the following technical effects:

[0054] The arc sweep simulation calculation research method of the full-size fan blade proposed in the present invention optimizes the simulation calculation process and improves the simulation calculation efficiency and convergence through a step-by-step research method for the simulation calculation of the fan blade damage characteristics under the arc sweep of the full-size fan blade, and supplements the research method of simulating the fan blade damage characteristics under the arc sweep action;

[0055] The present invention injects lightning waveforms at different electrode positions to simulate the movement process of fan blades under the sweeping action of lightning arcs, proposes a simulation calculation method for simulating the damage characteristics of fan blades under the action of lightning sweeping arcs, and analyzes the arc development path on the blade surface under the action of lightning sweeping. The method provides a theoretical research basis for non-conductive surface tests of different types of fan blades under arc sweeping, which saves the test cost to a certain extent; and can provide a basis for the damage development process and damage assessment of different areas of the blade, and provide ideas for its protection design, and provide verification means for the subsequent optimization of local protection of fan blades, thereby accelerating the research progress of fan blade protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The flowchart of the simulation calculation program for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc;

[0057] Figure 2 This is a schematic diagram of the typical area of ​​a fan blade;

[0058] Figure 3 Schematic diagram of electrode position in arc development simulation model;

[0059] Figure 4 is the waveform of lightning current (not to scale);

[0060] Figure 5 To verify the test diagram. DETAILED DESCRIPTION

[0061] The specific contents of the present invention are further explained in detail below in conjunction with embodiments.

[0062] This embodiment provides a simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc. The program flow chart is as follows: Figure 1 As shown, the following steps are included:

[0063] Step 1: Establish a full-scale model of a non-conductive surface wind turbine blade with a lightning receptor in a typical area, and determine the lightning waveform parameters and wind turbine blade material parameters;

[0064] The test device uses a full-scale model of the wind turbine blade lightning rod accessories, which includes the installation of the lightning rod and the blade, the connection between the lightning rod and the down conductor, the connection area between the two components and the non-conductive surface area of ​​the blade; the full-scale wind turbine blade model is as follows: Figure 2 As shown;

[0065] Wind turbine blade material parameter setting: Import a full-size wind turbine blade 3D model and set the material parameters of each area. The lightning receptor is made of metal, the blade surface is made of glass composite fiber material, the main beam is made of carbon fiber composite material, the down conductor is made of metal material, and the main beam and blade area are connected by adhesive.

[0066] Step 2: Place multiple electrodes at different positions of the blades and at a distance of ≥50 mm from the blades to establish a simulation calculation model for arc development of the wind turbine blades under the sweeping action of lightning arcs, and obtain physical parameters of the surface of the wind turbine blades;

[0067] Electrode settings in the simulation model: the electrode position is ≥50mm away from the blade, there is an arcing wire at the beginning of lightning, and the arcing wire is 20mm away from the sample. After the lightning is successfully connected, the arcing wire evaporates, and the lightning receptor is the anode surface; the electrode is located at different positions of the blade to simulate the movement process of the wind turbine blade; the lightning receptor, metal connectors, etc. are all grounding surfaces;

[0068] Boundary conditions: According to the lightning waveform parameters (such as Figure 4As shown in the figure, current density is injected at the electrode position, the lower end of the electrode is 50mm away from the blade surface, an arc-starting wire is added to the electrode area to the lightning receptor, the lightning receptor is simulated to be successfully connected, and the arc-starting wire is set to air at the moment of lightning channel breakdown to simulate the real lightning situation; the electrode and the sample are surrounded by air; the lightning receptor is connected to the down conductor and grounded;

[0069] Arc simulation calculation method:

[0070] Based on the magnetohydrodynamic arc model, an arc calculation model for full-size wind turbine blades is established; in order to simulate the influence of arc heat on nearby materials when the lightning arrester successfully blocks lightning, the arc-starting wire of the material establishes a lightning channel at the initial moment of the simulation model, and then the arc-starting wire evaporates, based on the following assumptions: (1) The arc fluid is in a stable state and the discharge is under atmospheric pressure; (2) The plasma is in a local thermal equilibrium state; (3) It is assumed that the thermodynamic and transmission characteristics of air are functions only related to temperature and are not affected by air pressure, simplifying the solution model; (4) The arc magnetohydrodynamic flow is laminar; (5) The gravity effect of particles in the plasma and viscous heating are not considered. The modules required for the numerical analysis of plasma discharge in the LTE state include the current module, magnetic field module, laminar flow module, fluid heat transfer module, and plasma equilibrium discharge module;

[0071] 1) Current module

[0072] In the lightning arc discharge model, the anode, cathode, and arc plasma regions use Maxwell's equations to model the electromagnetic field and obtain the current density parameters, as shown in the following formula:

[0073]

[0074] In the formula, is the magnetic field intensity vector, σ is the conductivity, is the electric field strength, is the magnetic flux density, μ0 is the magnetic permeability, is the electric displacement vector, ε is the dielectric constant, V is the electric potential, is the magnetic potential, is the current density, μ is the viscosity coefficient;

[0075] 2) Laminar flow module

[0076] The arc region in the time domain can use classical conservation equations to describe the flow phenomenon of magnetic fluid. The conservation equations include the mass conservation equation and momentum conservation equation in the fluid domain. The laminar flow region is the air region from the electrode to the blade surface.

[0077] The flow phenomenon of magnetic fluid in the arc region in the time domain can be described by the classical conservation equation. The conservation equation consists of two parts, as shown in the following equation:

[0078]

[0079] Equation (2) is the mass conservation equation in the fluid domain, and (3) is the momentum conservation equation. is the velocity vector, ρ is the density, p is the pressure, and I is the identity matrix;

[0080] 3) Heat transfer module

[0081] The arc plasma obeys the energy conservation equation based on the assumption of local thermal equilibrium, including arc heat flux, Joule heat, and external radiation energy loss.

[0082] Arc heat flux Q, Joule heat Q J , external radiation energy loss Q rad Calculated by the energy conservation equation, the calculation equation is as follows:

[0083]

[0084] In the formula, C p is the specific heat at constant pressure, T is the temperature, k is the thermal conductivity, k B is the Boltzmann constant, e is the charge of the electron, ε N is the plasma radiation coefficient; there is a small non-local thermal equilibrium layer on the contact surface between the anode and cathode and the arc plasma, and the problem can be solved by assuming the cathode temperature boundary condition.

[0085] 4) Heat transfer between the arc and the contact surface between the cathode and cathode

[0086] The heat change in the electrode area is related to its physical reaction process. The heat exchange equation at the anode and cathode is shown as follows:

[0087]

[0088] In the formula, q anode is the anode heat, q cathode is the cathode heat, q is the heat flow vector; n is the normal vector; J is the current density; φ a is the work function of the anode material; φ c is the cathode material work function; k B is the Boltzmann constant; V i is the air ionization energy; j i is the ion current; j e is the electron current.

[0089] According to the above calculation method, a damage characteristic simulation model of the fan blade is established. Figure 3 As shown;

[0090] The current density and heat flux density in the lightning arrester in the arc at the electrode position and in the vicinity of the arc extension path are extracted and calculated to provide data for establishing the current conduction and electro-thermal coupling simulation calculation model.

[0091] Step 3, based on the arc development simulation model of the full-size fan blade in step 2, a current conduction simulation calculation model of each region of the fan blade is established to obtain the current shunt characteristics of each region;

[0092] Based on the arc development model, the current density of the lightning receptor and the local area on the upper surface is obtained, and it is used as the input current load for the current conduction simulation calculation. The current conduction simulation calculation of the wind turbine blade is carried out. After the step-by-step simulation, it has better convergence and can save simulation time. The lightning current satisfies Ampere's law and the current conservation equation during the conduction process of the full-size wind turbine blade, as shown in the following formula:

[0093]

[0094] In the formula, is the current density of the external current source, is the unit current density, V is the electric potential, ε0 is the vacuum dielectric constant, ε r is the relative dielectric constant, μ0 is the vacuum magnetic permeability, μ r is the relative magnetic permeability, is the magnetic vector, For speed.

[0095] Step 4, establishing an electric-thermal-mechanical coupling simulation calculation model for each area of ​​the fan blade to obtain the damage characteristics of the fan blade;

[0096] The surface current density and internal current density obtained from the arc simulation and current conduction simulation in step 2 and step 3 are used as the current input of the component to study the damage influence law of the local area of ​​the fan blade and its electrical-thermal-mechanical coupling process, which follows the following equation:

[0097] 1) Electric field control equation

[0098] When the lightning current acts on the sample, the electric field obeys Maxwell's charge conservation equation. The finite element control equation of the electric field is as follows:

[0099]

[0100] Where V is the unit volume; S is the unit cross-sectional area, r c is the unit charge density, n is the external normal of surface S, E is the electric field intensity, σ E is the conductivity matrix; for the composite material σ E Anisotropy, for metal materials σ E Isotropic. is the cell volume current density; is the electric potential;

[0101] The Joule heat energy power of the current is:

[0102]

[0103] When a transient current flows, its energy formula is as follows:

[0104]

[0105] Where, t is time;

[0106] Electrical energy cannot be converted 100% into thermal energy. According to its conversion efficiency, the thermal energy formula is:

[0107] Q ce =ηP ce (10)

[0108] Where η is the conversion efficiency.

[0109] 2) Heat balance equation

[0110] According to the law of conservation of energy, the heat balance equation of the material heat conduction process during the lightning strike is as follows:

[0111] Q ce =Q c +Q d +Q f +Q s (11)

[0112] In the formula, Q c is the heat conduction energy, Q d is the thermal convection energy, Q f is the thermal radiation energy, Q s is the ablation heat energy.

[0113] From the steady-state Fourier heat conduction equation, we can get:

[0114]

[0115] Where ρ is density, U is internal energy, r is the heat generated in the volume, δ is the potential change function, and θ is the temperature change function.

[0116] 3) Thermal expansion equation

[0117] According to the thermal expansion equation, the thermal expansion stress distribution state of the local material during the simulation is as follows based on the thermal expansion equation and the basic equation of elasticity:

[0118]

[0119] Where b x 、b y 、b z They are the components of the volume force on the object material in the x, y, and z directions, and the strain force components are σ xx , σ xy and σ xz The thermal expansion stress distribution state of the local material during the simulation is calculated according to the above formula, and a stable solution is obtained by the electric-thermal-force field calculation. The electric-thermal-force coupling process of the material is analyzed to obtain the damage characteristics of each region.

[0120] The arc test of the fan blade under one of the fixed electrode positions is selected to verify the correctness of this simulation method. Figure 5 shown.

[0121] Step 5, by changing the electrode position, injecting lightning waveforms at different electrode positions to simulate the movement process of the wind turbine blades under the sweeping action of the lightning arc, and then simulating the development law of the arc action in various areas of the wind turbine blades under the action of the sweeping arc, and obtaining the arc development process, current distribution and damage characteristics of the wind turbine blades under the sweeping action of the lightning arc during the movement.

[0122] The simulation method for simulating the surface damage characteristics of wind turbine blades under the action of arc sweep can simulate the thermal effect damage to non-conductive materials on the blade surface during the lightning arc sweep process, as well as the affected characteristics of other areas. It solves the unclear problem of the current conduction path and the blade damage characteristics caused by the arc under the action of lightning arc sweep, saves test costs, accelerates the research process of lightning protection design for wind turbine blades, and can provide a research basis for lightning damage and protection design in various areas of wind turbine blades.

Claims

1. A simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc, characterized in that: The following steps are involved: Step 1: Establish a full-scale model of a non-conductive surface wind turbine blade with a lightning receptor in a typical area, and determine the lightning waveform parameters and wind turbine blade material parameters; Step 2: multiple electrodes are set at different positions of the blades with a distance of ≥50 mm from the blades, and a simulation calculation model of arc development of the wind turbine blades under the sweeping action of lightning arc is established to obtain the physical parameters of the surface of the wind turbine blades; Step 3, based on the arc development simulation model of the full-size fan blade in step 2, a current conduction simulation calculation model of each region of the fan blade is established to obtain the current shunt characteristics of each region; Step 4, establishing an electric-thermal-mechanical coupling simulation calculation model for each area of ​​the fan blade to obtain the damage characteristics of the fan blade; Step 5, by injecting lightning waveforms at different electrode positions to simulate the movement process of the wind turbine blades under the sweeping action of the lightning arc, and then simulating the development law of the arc action in each area of ​​the wind turbine blades under the action of the sweeping arc, the arc development process, current distribution and damage characteristics of the wind turbine blades under the sweeping action of the lightning arc during the movement are obtained.

2. A simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 1, characterized in that: The multiple electrodes described in step 2 are all connected to arc-starting wires, and a lightning channel is established through the arc-starting wires.

3. A simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 1 or 2, characterized in that: The calculation process of the arc development simulation calculation model described in step 2 includes: calculation of a current module, a laminar flow module, a heat transfer module, and a heat transfer module between the arc and the contact surface between the anode and cathode; The physical parameters of the fan blade surface in the arc arrester and the nearby area on the arc extension path at the electrode position are extracted from the calculation of the arc development simulation model; The physical parameters of the fan blade surface include current density, heat flux density and temperature distribution parameters.

4. A simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 3, characterized in that: The current module uses Maxwell's equations to model the electromagnetic field and obtain the current density parameters. The calculation equation is shown as follows: In the formula, is the magnetic field intensity vector, σ is the conductivity, is the electric field strength, is the magnetic flux density, μ0 is the magnetic permeability, is the electric displacement vector, ε is the dielectric constant, V is the electric potential, is the magnetic potential, is the current density, μ is the viscosity coefficient; The laminar flow module uses the classical conservation equation to describe the flow phenomenon of magnetic fluid. The calculation equation is shown as follows: Equation (2) is the mass conservation equation in the fluid domain, and (3) is the momentum conservation equation. is the velocity vector, ρ is the density, p is the pressure, and I is the identity matrix; Heat transfer module Arc heat flux Q, Joule heat Q J , external radiation energy loss Q rad Calculated by the energy conservation equation, the calculation equation is as follows: In the formula, C p is the specific heat at constant pressure, T is the temperature, k is the thermal conductivity, k B is the Boltzmann constant, e is the charge of the electron, ε N is the plasma radiation coefficient; The heat exchange equation for heat transfer between the arc and the contact surface of the anode and cathode is shown as follows: In the formula, q anode is the anode heat, q cathode is the cathode heat, q is the heat flow vector; n is the normal vector; J is the current density; φ a is the work function of the anode material; φ c is the cathode material work function; k B is the Boltzmann constant; V i is the air ionization energy; i is the ion current; j e is the electron current.

5. The simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 1, characterized in that: In the current conduction simulation calculation model of each area of ​​the fan blade described in step 3, the lightning current satisfies Ampere's law and the current conservation equation during the conduction process of the full-size fan blade. The calculation equation is shown as follows: Where: is the current density of the external current source, is the unit current density, V is the electric potential, ε0 is the vacuum dielectric constant, ε r is the relative dielectric constant, μ0 is the vacuum magnetic permeability, μ r is the relative magnetic permeability, is the magnetic vector, For speed.

6. The simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 1, characterized in that: The electric-thermal-mechanical coupling simulation calculation process described in step 4 includes: electric field, heat conduction and thermal expansion stress distribution states.

7. A simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 6, characterized in that: When the lightning current acts on the sample, the electric field obeys Maxwell's charge conservation equation. The finite element control equation of the electric field is as follows: Where V is the unit volume; S is the unit cross-sectional area, r c is the unit charge density, n is the external normal of surface S, E is the electric field intensity, σ E is the conductivity matrix; is the cell volume current density; is the electric potential; The Joule heat energy power of the current is: When a transient current flows, its energy formula is as follows: Where, t is time; According to its conversion efficiency, the thermal energy formula is: Q ce =ηP ce (10) Where η is the conversion efficiency.

8. The simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 6, characterized in that: The heat balance equation of the material heat conduction process during the lightning strike is shown as follows: Q ce =Q c +Q d +Q f +Q s (11) In the formula, Q c is the heat conduction energy, Q d is the heat convection energy, Q f is the thermal radiation energy, Q s It is the ablation heat energy. From the steady-state Fourier heat conduction equation, we can get: Where ρ is density, U is internal energy, r is the heat generated in the volume, δ is the potential change function, and θ is the temperature change function.

9. The simulation calculation method for simulating the surface damage characteristics of wind turbine blades under the sweep of lightning arc as claimed in claim 6, characterized in that: The thermal expansion stress distribution state of the local material during the simulation is obtained based on the thermal expansion equation and the basic equation of elasticity. The calculation equation is shown as follows: Where b x 、b y 、b z They are the components of the volume force on the object material in the x, y, and z directions, and the strain force components are σ xx , σ xy and σ xz .

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