Wind turbine noise propagation model design method based on refraction theory

Abstract

The invention discloses a wind turbine noise propagation model design method based on a refraction theory, which comprises the following steps of: 1) selecting sound sources, uniformly distributing the sound sources of a wind turbine at blade tips of three blades, and respectively calculating the propagation of the three sound sources; different rotation positions are selected in the blade rotation process to obtain a dynamic sound source; 2) calculation of sound propagation path simulation: calculating bending refraction in a sound propagation process based on a ray theory, drawing a sound propagation bending ray by using MATALAB programming, and calculating a ray length; 3) selecting a wake flow model, selecting an improved Gaussian wake flow model to calculate the wind turbine wake flow, and obtaining the wind speed at any space point; 4) calculating the air absorption, geometric diffusion and ground effect: calculating the attenuation condition of the air absorption part under different atmospheric working conditions. By calculating the noise influence in different ranges, the equipment waste and energy loss caused by unreasonable site selection and layout can be reduced, so that the design cost is reduced.

Description

Technical Field

[0001] The invention relates to the field of wind turbine noise propagation, and in particular to a wind turbine noise propagation model design method based on refraction theory. Background Art

[0002] In today's world, the reserves and distribution of energy play a vital role in the survival and development of a country. However, with the development of industry, the over-exploitation of primary energy has made energy shortages, environmental pollution, and global temperature rise increasingly prominent. In order to reduce the burning of fossil energy, improve the environment, and comprehensively coordinate sustainable development, wind energy, as a clean energy, has developed rapidly worldwide. More and more large wind turbines are installed on land and are getting closer and closer to where people live. The noise problem associated with the development of wind turbines is also increasingly affecting the lives of residents around wind farms. Therefore, it is very important to study the propagation of wind turbine noise, accurately calculate the noise level near wind farms, and predict the noise impact in different areas. Reliably calculating the noise from wind turbines to the receiving location has become an important task in the entire wind farm planning, design, and operation stages. This is not a simple task because the generation and propagation of wind farm noise involves complex mechanisms.

[0003] There are deficiencies in the existing technology for the study of wind turbine noise propagation: the research scope is limited, focusing on a single factor or specific scenario, lacking comprehensiveness and systematicness. The noise source analysis is insufficient, and the detailed generation mechanism and propagation characteristics of aerodynamic noise and mechanical noise are not studied in depth, especially aerodynamic noise is difficult to effectively suppress by conventional methods. The propagation path is not studied sufficiently, and there is little research on the propagation path, attenuation law and influencing factors of wind turbine noise in complex environments, resulting in limited accuracy of the prediction model; the impact assessment is imperfect, and the specific impact assessment of wind turbine noise on surrounding residential areas, ecological environment, etc. is not comprehensive enough, and there is a lack of long-term tracking monitoring data. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a wind turbine noise propagation model design method based on refraction theory. By calculating the noise impact in different ranges, it can reduce equipment waste and energy loss caused by unreasonable site selection and layout, thereby reducing design costs.

[0005] The object of the present invention is achieved by: a method for designing a wind turbine noise propagation model based on refraction theory, comprising the following steps:

[0006] 1) Selection of sound sources: evenly distribute the sound sources of the wind turbine at the tips of the three blades, and calculate the propagation of the three sound sources respectively; select different rotation positions during the rotation of the blades to obtain the dynamic sound source;

[0007] 2) Calculation of the simulation of the sound propagation path. Based on the ray theory, the bending and refraction of the sound propagation process are calculated. The sound propagation bending ray is drawn using MATLAB programming and the ray length is calculated.

[0008] 3) Selection of wake model: choose the improved Gaussian wake model to calculate the wind turbine wake and obtain the wind speed at any spatial point;

[0009] 4) Calculation of air absorption, geometric diffusion and ground effect: Select the air absorption calculation method in the engineering model of outdoor sound propagation, calculate the attenuation of the air absorption part under different atmospheric conditions; and calculate the total sound pressure level through the three calculation results.

[0010] As a further limitation of the present invention, step 1) specifically includes: dividing the wind turbine sound source into three point sound sources, the sound source position is placed at the tips of the three blades, the three sound sources emit sound rays, which arrive at the receiving position respectively, and calculating the superposition and cancellation of the three sound rays with different phases to obtain the noise at the receiving position; since the blades are rotating, the position of the blades is constantly changing, the distribution of the wind turbine blades is average, and is periodic during the rotation process, and the position selection only needs to consider the different positions taken on average during the blade rotation of 0° to 120°.

[0011] As a further limitation of the present invention, the step 2) specifically comprises:

[0012] The wind turbine sound propagation path simulation calculation method based on ray theory is selected. The calculation formula is as follows:

[0013]

[0014] In a non-refracting atmosphere, the wavefront of a point sound source is spherical. In a refractive atmosphere, the spherical surface is deformed by refraction, and the curved wavefront can be locally approximated by a plane wavefront. The propagation of such a plane wave follows the theory of refraction. The curved sound rays from a point sound source conform to the theory of refraction of sound rays.

[0015] In the formula, z is the height, c is the speed of sound, and the speed of sound calculation formula is Among them, k is the ratio of the specific heat at constant pressure to the specific heat at constant volume, R is the gas constant, T(z) is the temperature at the corresponding height, v(z) is the speed of sound at the corresponding height, γ is the angle between the local speed of sound curve and the horizontal plane where it is located, and C is a constant. On a speed of sound curve, C is a constant value.

[0016] As a further limitation of the present invention, the step 3) specifically includes: calculating the wind speed in the wake using an improved Gaussian wake model, and the wind speed calculation formula is:

[0017]

[0018] Where U0 is the inflow wind speed at hub height, α is the wind shear index, and z h is the hub height;

[0019] Parameter calculation, wake shape parameters:

[0020] Define the intermediate parameters: a=1.216,

[0021] Wake center loss Define the intermediate parameters:

[0022] Among them, r w is the wake width radius, C T is the thrust coefficient, I a is the hub height turbulence intensity, κ is the wake expansion index, s = x / D, D is the wind turbine rotor diameter, r d is the radius of the wind turbine rotor, d0 is the diameter of the wind turbine rotor, x is the downstream distance of the wind turbine; r is the distance between the sound receiving position and the centerline of the wake.

[0023] As a further limitation of the present invention, the step 4) specifically comprises:

[0024] Air absorption calculation: Sound absorption in air is due to shear viscosity, thermal conductivity or heat dissipation, and molecular relaxation caused by vibration, rotation and translational kinetic energy of oxygen, nitrogen and water vapor. The sound attenuation caused by air absorption is recorded as:

[0025]

[0026] Where d is the path length of the traveling wave, in meters; P(d) is the sound pressure after a distance d; P(0) is the initial sound pressure when d = 0; α1 is the attenuation coefficient, in neper meters; a is the attenuation coefficient, in decibels per meter;

[0027] Diffusion losses depend on the pressure, relative humidity, and frequency of air in a still atmosphere; the attenuation coefficient of sound is given by,

[0028]

[0029] Where, F = f / p s , F d,o =f d,o / p s , F d,N =f d,N / ps , f is the frequency of the sound, the unit is Hz; p s is the atmospheric pressure; p s0 is the reference atmospheric pressure, which is 1 atm; T is the atmospheric temperature, in K; T0 is the reference temperature, which is 293.15 K; f d,o is the relaxation frequency of oxygen molecules; f d,N is the relaxation frequency of nitrogen molecules;

[0030] The relaxation frequency formula of oxygen and nitrogen ratio is:

[0031]

[0032]

[0033] Where h is the percentage of the molar concentration of water vapor; h is calculated based on the relative humidity h d The calculation results are: Saturated steam T 01 =273.16;

[0034] Geometric diffusion calculation, geometric diffusion considers that the point sound source propagates spherically in the free field, and the attenuation value is:

[0035]

[0036] Where d is the distance from the sound source to the receiver in meters; d0 is the reference distance, d0 = 1; the constant in the formula relates the sound power level to the sound pressure level at a reference distance d0 of 1 meter from the omnidirectional point source;

[0037] Calculation of ground effect: Sound rays will be reflected when they reach the ground, and will be reflected once or multiple times to reach the receiving position. The contribution to the sound pressure level at the receiving position is calculated as follows:

[0038]

[0039] Where Q = R p , R p is the plane wave reflection coefficient, R d is the direct propagation path, R r is the propagation path after reflection, Q is the spherical wave reflection coefficient, i is the imaginary unit, and k is the wave number.

[0040] The present invention adopts the above technical solution, and compared with the prior art, the beneficial effects are as follows: the present invention adopts ray theory calculation, simulates the propagation path of sound, takes into account the wake effect of the wind turbine, and selects an accurately calculated engineering model to calculate the attenuation of the air absorption part; considers the dynamic effect of the sound source, close to the actual operation of the wind turbine; by calculating the noise impact in different ranges, it can reduce equipment waste and energy loss caused by unreasonable site selection and layout, thereby reducing design costs. In terms of operating costs, the impact of wind turbine noise on residents is within a reasonable range, reducing the contradiction between residents and wind farm operations, thereby reducing operating costs; in terms of wind power development, the impact of wind turbine noise on residents is within the prescribed standards, which improves residents' acceptance of wind power generation, reduces the development resistance of wind power generation, and helps the development of the wind power industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a model flow chart of the present invention.

[0042] Figure 2 A schematic diagram of microphone positions for sound propagation calculation and verification provided by the present invention.

[0043] Figure 3 The present invention provides a sound ray propagation path diagram drawn based on the ray theory calculation of the wind turbine noise propagation path.

[0044] Figure 4 The figure shows the wind speed of the wind turbine wake under the calculated working condition drawn by the wake model of the present invention.

[0045] Figure 5 The present invention uses the new model to perform calculations in working condition 1 and compares them with experimental data, and also compares the calculation results with ISO model and WindSTAR model.

[0046] Figure 6 The present invention uses the new model to perform calculations in working condition 2 and compares the results with experimental data, and also compares the calculation results with ISO model and WindSTAR model. DETAILED DESCRIPTION

[0047] like Figure 1 A wind turbine noise propagation model design method based on refraction theory is shown, comprising the following steps:

[0048] 1) Selection of sound sources: evenly distribute the sound sources of the wind turbine at the tips of the three blades, and calculate the propagation of the three sound sources respectively; select different rotation positions during the rotation of the blades to obtain the dynamic sound source;

[0049] The sound source of the wind turbine is divided into three point sound sources. The sound source position is placed at the tips of the three blades. The three sound sources emit sound rays that arrive at the receiving position respectively. The superposition and cancellation of the three sound rays with different phases are calculated to obtain the noise at the receiving position. Since the blades are rotating, the position of the blades is constantly changing. The distribution of the wind turbine blades is even and periodic during the rotation process. The position selection only needs to consider the average of different positions during the blade rotation of 0° to 120°.

[0050] 2) Calculation of the simulation of the sound propagation path. Based on the ray theory, the bending and refraction of the sound propagation process are calculated. The sound propagation bending ray is drawn using MATLAB programming and the ray length is calculated.

[0051] The wind turbine sound propagation path simulation calculation method based on ray theory is selected. The calculation formula is as follows:

[0052]

[0053] In a non-refracting atmosphere, the wavefront of a point sound source is spherical. In a refractive atmosphere, the spherical surface is deformed by refraction, and the curved wavefront can be locally approximated by a plane wavefront. The propagation of such a plane wave follows the theory of refraction. The curved sound rays from a point sound source conform to the theory of refraction of sound rays.

[0054] In the formula, z is the height, c is the speed of sound, and the speed of sound calculation formula is Wherein, k is the ratio of the specific heat at constant pressure to the specific heat at constant volume, R is the gas constant, k=1.4, R=287, T(z) is the temperature at the corresponding height, v(z) is the speed of sound at the corresponding height, γ is the angle between the local speed of sound curve and the horizontal plane where it is located, and C is a constant. On a speed of sound curve, C is a constant value.

[0055] 3) Selection of wake model: choose the improved Gaussian wake model to calculate the wind turbine wake and obtain the wind speed at any spatial point;

[0056] The improved Gaussian wake model is used to calculate the wind speed in the wake. The wind speed calculation formula is:

[0057]

[0058] Where U0 is the inflow wind speed at hub height, α is the wind shear index, and z h is the hub height;

[0059] Parameter calculation, wake shape parameters:

[0060] Define the intermediate parameters: a=1.216,

[0061] Wake center loss Define the intermediate parameters:

[0062] Among them, r w is the wake width radius, C T is the thrust coefficient, I a is the hub height turbulence intensity, κ is the wake expansion index, κ = 0.4, s = x / D, D is the wind turbine rotor diameter, r d is the radius of the wind turbine rotor, d0 is the diameter of the wind turbine rotor, x is the downstream distance of the wind turbine; r is the distance between the sound receiving position and the centerline of the wake.

[0063] 4) Calculation of air absorption, geometric diffusion and ground effect: Select the air absorption calculation method in the engineering model of outdoor sound propagation, calculate the attenuation of the air absorption part under different atmospheric conditions; and calculate the total sound pressure level through the three calculation results;

[0064] Air absorption calculation: Sound absorption in air is due to shear viscosity, thermal conductivity or heat dissipation, and molecular relaxation caused by vibration, rotation and translational kinetic energy of oxygen, nitrogen and water vapor. The sound attenuation caused by air absorption is recorded as:

[0065]

[0066] Where d is the path length of the traveling wave, in meters; P(d) is the sound pressure after a distance d; P(0) is the initial sound pressure when d = 0; α1 is the attenuation coefficient, in neper meters; a is the attenuation coefficient, in decibels per meter;

[0067] Diffusion losses depend on the pressure, relative humidity, and frequency of air in a still atmosphere; the attenuation coefficient of sound is given by,

[0068]

[0069] Where, F = f / p s , F d,o =f d,o / p s , F d,N =f d,N / p s , f is the frequency of the sound, the unit is Hz; p s is the atmospheric pressure; p s0 is the reference atmospheric pressure, which is 1 atm; T is the atmospheric temperature, in K; T0 is the reference temperature, which is 293.15 K; f d,o is the relaxation frequency of oxygen molecules; f d,Nis the relaxation frequency of nitrogen molecules;

[0070] The relaxation frequency formula of oxygen and nitrogen ratio is:

[0071]

[0072] Where h is the percentage of the molar concentration of water vapor; h is calculated based on the relative humidity h d The calculation results are: Saturated steam T 01 =273.16;

[0073] Geometric diffusion calculation, geometric diffusion considers that the point sound source propagates spherically in the free field, and the attenuation value is:

[0074]

[0075] Where d is the distance from the sound source to the receiver in meters; d0 is the reference distance, d0 = 1; the constant in the formula relates the sound power level to the sound pressure level at a reference distance d0 of 1 meter from the omnidirectional point source;

[0076] Calculation of ground effect: Sound rays will be reflected when they reach the ground, and will be reflected once or multiple times to reach the receiving position. The contribution to the sound pressure level at the receiving position is calculated as follows:

[0077]

[0078] Where Q = R p , R p is the plane wave reflection coefficient, R d is the direct propagation path, R r is the propagation path after reflection, Q is the spherical wave reflection coefficient, i is the imaginary unit, and k is the wave number.

[0079] The implementation of the method of the present invention is further described:

[0080] Step 1) Calculate the wind turbine wake to obtain the wind speed at any point in space; see Table 1 for different working conditions. Figure 4 (a) and (b) are the wake of working condition 1 and working condition 2.

[0081] Table 1

[0082]

[0083] Step 2) The wind turbine point sound source is divided into three point sound sources, which are placed at the tips of the three blades respectively. The three sound sources emit sound rays, which reach the receiving positions respectively. Twelve positions are selected on average when the blade rotates 0° to 120°, and calculations are performed for each rotation position. Finally, the total sound pressure level of the twelve positions is averaged.

[0084] Step 3) Take a rotation position for detailed description. First, determine the position of the tip of the three blades, calculate the propagation path formed by the sound ray emitted from the tip to the receiving position, and use the refraction theory to calculate the angle between the ray of the step length and the horizontal plane. The propagation ray of the step length is obtained, and the ray calculation of the next step length is performed on the basis of the propagation of the step length until it propagates to the receiving position. Since the sound ray is emitted at different angles, the sound ray arrives at different positions. It is necessary to find the propagation path to the specified position. Set the initial emission angle from -60° to 30° (adjustable according to the actual calculation situation), the step length is 0.001°, and calculate in a loop to find the corresponding sound ray. Figure 3 (a) is one of the sound rays.

[0085] Step 4) Calculate air absorption and geometric diffusion attenuation. The path in the formula is the calculated propagation path length. Calculate the ground effect. The sound ray will reflect and continue to propagate when it hits the ground. After one or more reflections, if the sound ray hits the receiving position, it will have a superposition or cancellation effect on the sound received at the receiving position. The calculation method is the same as step 3. The ray will reflect after reaching the ground. After reflection, the ray will continue to propagate according to the refraction theory. The sound ray passing through the receiving position is retained. Figure 3 (b) is one of the reflected sound rays. It is used to calculate the ground effect. The calculation result is L = sound source sound power - air absorption - geometric diffusion + ground effect; the sound source of the wind turbine is emitted from the three blade tips and propagates to the receiving position. The total sound pressure level is calculated from the three calculation results.

[0086] Step 5) Set unknowns for the sound power of sound sources with different frequencies in the 1 / 3 octave band, and use the propagation method from step 1) to step 4) to calculate the propagation to the IEC microphone (the microphone is placed Figure 2 The result with unknowns is calculated and the expression with unknowns is combined with the experimental data measured by the IEC microphone to solve for the sound power of the sound source. The sound power of the sound source is then emitted from the sound source and propagated using steps 1) to 4) to propagate to microphones 5, 6, 7 and 8. Microphone 5, microphone 6, microphone 7 and microphone 8 are 506.2 meters, 706.02 meters, 858 meters and 978.5 meters away from the wind turbine respectively, and are placed from the near field to the far field of the wind. Figure 5 , Figure 6The figures are comparison diagrams of the calculated sound pressure levels of wind turbines at microphone 5 (a), microphone 6 (b), microphone 7 (c), and microphone 8 (d) under working conditions 1 and 2 respectively; the figures compare the experimental values ​​(Measurement Data), the parabolic equation solution method (WindSTAR), the engineering model of the International Organization for Standardization (ISO9613-2), and the new method (New model) proposed in the present invention; it can be seen from the figures that the results of the new method are highly consistent with the experimental values ​​and have a fast calculation speed.

[0087] The present invention provides a wind turbine noise propagation model design method based on refraction theory, adopts ray theory calculation, simulates the sound propagation path, takes into account the wake effect of the wind turbine, selects an accurate engineering model to calculate the attenuation of the air absorption part; takes into account the dynamic effect of the sound source, close to the actual operation of the wind turbine; by calculating the noise impact in different ranges, it can reduce equipment waste and energy loss caused by unreasonable site selection and layout, thereby reducing design costs.

[0088] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A wind turbine noise propagation model design method based on refraction theory, characterized in that: The following steps are involved: 1) Selection of sound sources: evenly distribute the sound sources of the wind turbine at the tips of the three blades and calculate the propagation of the three sound sources respectively; Different rotation positions are selected during the blade rotation process to obtain a dynamic sound source; 2) Calculation of the simulation of the sound propagation path. Based on the ray theory, the bending and refraction of the sound propagation process are calculated. The sound propagation bending ray is drawn using MATLAB programming and the ray length is calculated. 3) Selection of wake model: choose the improved Gaussian wake model to calculate the wind turbine wake and obtain the wind speed at any spatial point; 4) Calculation of air absorption, geometric diffusion and ground effect: Select the air absorption calculation method in the engineering model of outdoor sound propagation to calculate the attenuation of the air absorption part under different atmospheric conditions; And the total sound pressure level is calculated through three calculation results.

2. The method for designing a wind turbine noise propagation model based on refraction theory according to claim 1, characterized in that: The step 1) specifically includes: dividing the sound source of the wind turbine into three point sound sources, the sound source position is placed at the blade tips of the three blades, the three sound sources emit sound rays, which arrive at the receiving positions respectively, and calculating the superposition and cancellation of the three sound rays with different phases to obtain the noise at the receiving position; since the blades are rotating, the positions of the blades are constantly changing, the distribution of the wind turbine blades is average, and has periodicity during the rotation process, and the position selection only needs to consider the different positions taken on average during the process of the blades rotating 0° to 120°.

3. The method for designing a wind turbine noise propagation model based on refraction theory according to claim 1, characterized in that: The step 2) specifically includes: The wind turbine sound propagation path simulation calculation method based on ray theory is selected. The calculation formula is as follows: In a non-refracting atmosphere, the wavefront of a point sound source is spherical. In a refractive atmosphere, the spherical surface is deformed by refraction, and the curved wavefront can be locally approximated by a plane wavefront. The propagation of such a plane wave follows the theory of refraction. The curved sound rays from a point sound source conform to the theory of refraction of sound rays. In the formula, z is the height, c is the speed of sound, and the speed of sound calculation formula is Among them, k is the ratio of the specific heat at constant pressure to the specific heat at constant volume, R is the gas constant, T(z) is the temperature at the corresponding height, v(z) is the speed of sound at the corresponding height, γ is the angle between the local speed of sound curve and the horizontal plane where it is located, and C is a constant. On a speed of sound curve, C is a constant value.

4. The method for designing a wind turbine noise propagation model based on refraction theory according to claim 1, characterized in that: The step 3) specifically includes: using an improved Gaussian wake model to calculate the wind speed in the wake, and the wind speed calculation formula is: Where U0 is the inflow wind speed at hub height, α is the wind shear index, and z h is the hub height; Parameter calculation, wake shape parameters: Define the intermediate parameters: a=1.216, Wake center loss Define the intermediate parameters: Among them, r w is the wake width radius, C T is the thrust coefficient, I a is the hub height turbulence intensity, κ is the wake expansion index, s = x / D, D is the wind turbine rotor diameter, r d is the radius of the wind turbine rotor, d0 is the diameter of the wind turbine rotor, x is the downstream distance of the wind turbine; r is the distance between the sound receiving position and the centerline of the wake.

5. The method for designing a wind turbine noise propagation model based on refraction theory according to claim 1, characterized in that: The step 4) specifically includes: Air absorption calculation: Sound absorption in air is due to shear viscosity, thermal conductivity or heat dissipation, and molecular relaxation caused by vibration, rotation and translational kinetic energy of oxygen, nitrogen and water vapor. The sound attenuation caused by air absorption is recorded as: Where d is the path length of the traveling wave, in meters; P(d) is the sound pressure after a distance d; P(0) is the initial sound pressure when d = 0; α1 is the attenuation coefficient, in neper meters; a is the attenuation coefficient, in decibels per meter; Diffusion losses depend on the pressure, relative humidity, and frequency of air in a still atmosphere; the attenuation coefficient of sound is given by, Where, F = f / p s , F d,o =f d,o / p s , F d,N =f d,N / p s , f is the frequency of the sound, the unit is Hz; p s is the atmospheric pressure; p s0 is the reference atmospheric pressure, which is 1 atm; T is the atmospheric temperature, in K; T0 is the reference temperature, which is 293.15 K; f d,o is the relaxation frequency of oxygen molecules; f d,N is the relaxation frequency of nitrogen molecules; The relaxation frequency formula of oxygen and nitrogen ratio is: Where h is the percentage of the molar concentration of water vapor; h is calculated based on the relative humidity h d The calculation results are: Saturated steam T 01 =273.16; Geometric diffusion calculation, geometric diffusion considers that the point sound source propagates spherically in the free field, and the attenuation value is: Where d is the distance from the sound source to the receiver in meters; d0 is the reference distance, d0 = 1; the constant in the formula relates the sound power level to the sound pressure level at a reference distance d0 of 1 meter from the omnidirectional point source; Calculation of ground effect: Sound rays will be reflected when they reach the ground, and will be reflected once or multiple times to reach the receiving position. The contribution to the sound pressure level at the receiving position is calculated as follows: Where Q = R p , R p is the plane wave reflection coefficient, R d is the direct propagation path, R r is the propagation path after reflection, Q is the spherical wave reflection coefficient, i is the imaginary unit, and k is the wave number.

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