Empirical formula suitable for calculating urban suburb turbulence intensity

Abstract

The invention relates to an empirical formula suitable for calculating turbulence intensity in suburban areas, and belongs to the fields of meteorology, physics, mechanics, renewable energy source application basic theories and application technology research thereof. Wind data of three consecutive years are measured through experiments, different exponential law functions are taken as function sources by referring to previous research, the law of the wind data is found to be consistent with the law of an exponential function through fitting, and the exponential function is taken as an empirical formula. Value ranges of three parameters in the empirical formula at different heights are obtained through repeated fitting and comparison argumentation, and a function relational expression between two parameters in power is obtained through data fitting. The method has the beneficial effects that an empirical formula suitable for calculating the turbulence intensity of the suburban area is obtained, a scientific basis is provided for calculation of the turbulence intensity at different heights, and the method has practical significance on wind energy utilization in the suburban area and selection and operation of a wind turbine generator.

Description

Technical Field

[0001] The invention relates to obtaining an empirical formula that can more accurately express the turbulence intensity at different heights in urban suburban areas, and belongs to the research field of meteorology, physics, mechanics, basic theory of renewable energy application and its application technology. Background Art

[0002] In recent years, due to the intensification of global warming and other issues, as well as people's demand for sustainable development, renewable energy has gradually attracted people's attention. Wind energy, as the fastest-growing clean energy, has broad development prospects. my country's suburban areas are rich in wind energy resources. Effective use of wind energy in suburban areas is one of the measures to reduce urban air pollution and alleviate urban energy shortages. However, there are still many problems with the use of suburban wind energy, such as weak design foundation of wind turbines and inaccurate selection, which leads to damage to wind turbines. In order to make more effective use of wind energy, it is necessary to calculate the turbulence intensity at different heights in order to reasonably and accurately select wind turbines and ensure the normal operation and daily maintenance of wind turbines.

[0003] Turbulence intensity describes the degree of change of wind speed over time and space, reflects the relative intensity of pulsating wind speed, and is the most important characteristic quantity for describing the motion characteristics of atmospheric turbulence. In the past, research on turbulence intensity was mainly based on field experiments and measurements, but there are many factors that affect turbulence intensity, and the empirical formula for calculating turbulence intensity using height is relatively single in scope of application. Considering the influence of multiple factors, there are few calculation formulas suitable for calculating turbulence intensity in suburban areas. Based on this, this paper uses different exponential law functions to fit and analyze the experimental wind speed data collected in suburban areas, so as to select the exponential law function with better fitting goodness for research. Therefore, this paper proposes a new method based on the calculation of turbulence intensity at different heights in suburban areas as the core problem.

[0004] The proposal of a new method for calculating turbulence intensity in suburban areas is extremely important for solving practical problems. By studying turbulence intensity at a high altitude, a scientific basis can be provided for the selection of wind turbines, thereby providing a guarantee for the normal operation of wind turbines. Based on this, this paper proposes an empirical formula for calculating turbulence intensity in suburban areas at different altitudes, namely the TH-type turbulence intensity empirical formula, which is of great significance to the utilization of wind energy in suburban areas and the selection and operation of wind turbines. Summary of the invention

[0005] Aiming at the problem that the turbulence intensity values ​​at different altitudes cannot be accurately obtained, the present invention provides a novel empirical formula suitable for calculating the turbulence intensity in suburban areas.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] 1. Experimental platform construction

[0008] The ZephIR 300 lidar wind measurement system platform was used as the main experimental equipment. The measurement location was arranged in the wind tunnel laboratory of Inner Mongolia University of Technology. Three different adjustable lidar test height ranges were set to collect wind speed and direction data at the observation stations at altitudes of 10-38m, 10-99m and 10-199m.

[0009] 2. Experimental data measurement

[0010] The experimental data gives the physical meaning of the parameters by adjusting the test height of the radar. Phase I: The test point height is 10-38m, the collection time is from April 2017 to March 2018, the time period is about one year, and 578,160 wind speed and wind direction data should be collected within one year, of which 492,147 are valid data. Phase II: The test point height is 10-99m, the collection time is from July 2018 to June 2019, the time period is about one year, and 578,160 wind speed and wind direction data should be collected within one year, of which 367,920 are valid data. Phase III: The test point height is 10-199m, the collection time is from July 2019 to June 2020, the time period is about one year, and 578,160 wind speed and wind direction data should be collected within one year, of which 492,147 are valid data.

[0011] 3. Function determination

[0012] Turbulence intensity is defined as the ratio of the standard deviation of wind speed to the mean wind speed, calculated using the same set of measurement data and a specified period. The formula for 10-minute turbulence intensity is shown in (1-3).

[0013] (1-3) In formula (1-3): T i is the turbulence intensity; σ is the root mean square of the pulsating wind speed, m / s; v is the average wind speed, m / s.

[0014] According to the 2005 version of IEC 61400-1, turbulence intensity is divided into three levels: A, B, and C, where A is high turbulence intensity, B is medium turbulence intensity, and C is low turbulence intensity. Wind load specifications in many countries propose that the downwind turbulence intensity Iu(z) can be expressed in an exponential form, and the function is shown in formula (1-4).

[0015] (1-4) In formula (1-4): z is the height of the measuring point.

[0016] Combined with previous studies, different exponential functions were used as function sources, and the measured data were substituted into the function sources for fitting. The relationship between turbulence intensity and the height of the measuring point was studied, and the goodness of fit values ​​of different exponential functions were compared. A function formula suitable for calculating turbulence intensity values ​​at different heights was summarized, which has a high goodness of fit for the measured wind field. This exponential function was used as the research object of turbulence intensity in the suburbs of the city and was named TH (Turbulence intensity -Height) type turbulence intensity function. This function is shown in formula (1-5).

[0017] Function formula:

[0018] (1-5) In formula (1-5): T i is TH type turbulence intensity; x is the height of the measuring point, m; a is the turbulence intensity; b is the reference height, m; c is the correction height, m.

[0019] According to the dimensional analysis method, x is the height, and parameters b and c are both height parameters. After fitting, it is found that the function formula has a certain range of applicability for calculating turbulence intensity at different heights. At different heights, the value of parameter a has a certain range and its goodness of fit is high.

[0020] Analyzing formula (1-5), when b / (x+c) approaches 0, that is, when x is larger or b approaches 0, T i The value is approximately equal to the a value, and the a value is the magnitude of the turbulence intensity, that is, the TH-type turbulence intensity T related to the height is obtained. i The value of .

[0021] Since the three parameters a, b, and c belong to the relationship of multi-factor interaction, the change of one of the parameters will inevitably lead to the change of the other two parameters.

[0022] For formula (1-5), parameter b and parameter c jointly affect parameter a. Formula (1-6) has the highest fitting degree and can better reflect the relationship between parameter b and parameter c.

[0023] The relationship between parameters b and c can be expressed by formula (1-6):

[0024] (1-6) In formula (1-6): M, N, K are relevant parameters.

[0025] 4. Spatial characteristics analysis of empirical formula

[0026] In order to obtain a more accurate empirical formula, the ZephIR 300 lidar test system was combined to obtain three consecutive years of experimental measurement data, fit different exponential functions, and conduct comparative analysis.

[0027] The measurement method of increasing the height year by year was adopted, from the measurement range of 10-38m during 2017.4-2018.3, to the measurement range of 10-99m during 2018.7-2019.6, and then to the measurement range of 10-199m during 2019.7-2020.6. The distribution accuracy of different measurement height ranges was adjusted respectively, and the measurement accuracy increased from 1m to 10m. The quantitative analysis method was adopted, combined with the determination coefficient R 2 , Chi-square X 2 , residual sum of squares SSE test, determination coefficient R 2 The closer to 1, the 2 The closer the SSE is to 0, the higher the fitting accuracy. 2 , X2, SSE value distribution Figure 1 It shows that the goodness of fit of the function formula meets the actual measured wind speed distribution in this area. Therefore, based on the function fitting of each observation point, the results consistently show that the exponential function can be used as an empirical formula for calculating turbulence intensity at different heights in suburban areas.

[0028] 5. Analysis of time characteristics of empirical formula

[0029] The study of wind profiles is mostly fitted with full-year measurement data. In order to further study the fit of the exponential function in the suburban areas of the city, the time characteristic analysis method is used to study the wind environment in Hohhot through the wind speed and wind direction data collected by the ZephIR 300 laser radar. Different measurement heights are arranged to fit the local wind speed of the suburban wind environment in Hohhot according to different months. The measurement method of increasing the height year by year is adopted, from the measurement range of 10-38m from 2017.4 to 2018.3, to the measurement range of 10-99m from 2018.7 to 2019.6, to the measurement range of 10-199m from 2019.7 to 2020.6, to analyze the fitting of the empirical formula. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figures 1 to 3 Fitting R for three consecutive years 2 , X 2 , SSE value distribution diagram; Figure 4 For the flow chart. Implementation

[0031] The principles and features of the present invention are described below in conjunction with the accompanying drawings:

[0032] The first step is to build an experimental platform. This time, the ZephIR 300 lidar wind measurement system platform is used as the main experimental equipment, and the measurement location is arranged at the Energy Base of Inner Mongolia University of Technology.

[0033] The second step is to measure the experimental data and obtain three consecutive years of experimental measurement data. Different exponential law functions are listed as function sources, and the measured data are substituted into the function sources for fitting, and the fitting goodness of fit values ​​of different exponential functions are compared.

[0034] The third step is to analyze and derive an empirical formula suitable for calculating turbulence intensity at different heights in suburban areas based on the goodness of fit. Through fitting research, the functional relationship between parameters b and c in the empirical formula is obtained.

[0035] The fourth step is to conduct a comprehensive analysis based on the temporal and spatial characteristics and the spatial characteristics, and it is concluded that the empirical formula has the highest goodness of fit and is most suitable for the study of turbulence intensity in the suburbs of cities.

[0036] The fifth step is to apply the function according to actual needs. The empirical formula provided in this paper can provide a more accurate method for calculating turbulence intensity at different heights, provide a better theoretical basis for the selection of wind turbines in suburban areas, and provide effective support for the calculation method of wind resources in suburban areas, thereby achieving the purpose of effectively utilizing wind energy in suburban areas and accurately selecting wind turbines.

Claims

1. An empirical formula suitable for calculating turbulence intensity at different heights in urban suburbs. The function determination feature is: based on previous studies, different exponential functions are used as function sources, three years of measured data are substituted into the function source for fitting, and the goodness of fit of each function is compared and analyzed. An empirical formula for calculating turbulence intensity at different heights was obtained, which has a high goodness of fit for the measured wind field. This exponential function was used as an empirical formula for calculating turbulence intensity in urban suburbs, and the value ranges of each parameter in the function at different heights were analyzed and summarized. The functional relationship between the parameters in the formula was obtained through fitting.

2. Function formula: (1-1).

3. See formula (1-1): T i is TH type turbulence intensity; x is the height of the measuring point, m; a is the turbulence intensity; b is the reference height, m; c is the correction height, m.

4. Functional relationship between parameters: (1-2).

5. See formula (1-2): M, N, K are related parameters.

6. An empirical formula for calculating turbulence intensity at different altitudes in urban suburbs, with analysis of its spatial characteristics, characterized by: Different exponential law functions were fitted and compared. The measurement method of increasing the height year by year was adopted to adjust the distribution accuracy of different measurement height ranges, and the measurement accuracy increased from 1m to 10m. The quantitative analysis method was adopted to remove individual bad values ​​through analysis, and the determination coefficient R was combined with the 2 , Chi-square X 2 , residual sum of squares SSE test, determination coefficient R in Figure 1 2 Close to 1, X 2 The SSE is close to 0, the fitting accuracy is high, and the goodness of fit of the exponential function meets the actual measured wind speed distribution in this area. Therefore, based on the function fitting of each observation point, the results consistently show that the exponential function can be used as an empirical formula for calculating turbulence intensity in suburban areas.

7. An empirical formula for calculating turbulence intensity at different altitudes in urban suburbs, with analysis of its time characteristics, characterized by: The study of turbulence intensity uses the measurement data throughout the year for fitting. In order to further study the fit of the empirical formula for calculating turbulence intensity in the suburban areas of the city, the wind environment in the suburban areas of Hohhot is studied by using the wind speed and wind direction data collected by the ZephIR 300 laser radar using the time characteristic analysis method. Different measurement heights are arranged to fit the local wind speed of the suburban wind environment of Hohhot according to different months. The measurement method of increasing the height year by year is used to analyze the fitting of the empirical formula and conduct a comparative analysis.

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