| The system research on wind shear index of temporal and spatial variation in different terrain conditions of China is rarely restricted by low-altitude wind detecting condition. Only in recent years, low-altitude wind speed observation data above 10 m was provided by wind towers established for wind energy development which make up insufficient conventional weather stations within only 10 m near-surface wind direction and speed observations. This data is very important to the study on the atmospheric boundary layer, especially to to the study on characteristic of the wind field near the surface layer.The research collated and analyzed wind data of 138 towers.The system research on wind shear index of temporal and spatial variation in different terrain conditions of China was established.The research was used wind speed data of 138 wind towers nationwide. Types of wind nemometer are NRG and Secondwind which were calibrated, the heights are 50 to 100 m of wind towers, Wind speed of wind towers was analyzed and counted through soft programming on the research. The data of different hight was selected which every high layer sample quantity is more than 70, These samples were 10 m, 30 m, 50 m and 70 m. The spatial distribution of the wind shear index of these heights was mapped by Arc GIS, then the result was analyzed and summarized.The research focused on the wind shear index of the inland areas and coastal areas.The inland areas are inland plains, hills, plateaus, mountains, coastal areas are North China Coastal and South China Coastal. The research defines these areas in detail with uniform standards in order to improve the reliability of the results and accuracy of the background. In order to improve the reliability of comparison, the wind shear index was calculated using wind speed at different heights of the towers in a year of the same area and terrain, and then get the monthly and hourly wind shear index, The monthly variation and diurnal variation characteristic of the inland coastal wind shear index was analyzed and summarized.The research show that wind shear index range is from-0.1732 to 0.6904, according to wind shear index range, combined with the international definition of the size of the wind shear exponent which 1/7 is defined as a moderate, the wind shear index of the surface layer is divided into 5 grades which is very small(less than 0), smaller(0~0.1), medium(0.1~0.2), larger(0.2~0.3)and great(>0.3) respectively. The propotion of wind shear index calculated by the sample wind towers is most between 0.1 and 0.2 which is 42~48%, less between 0 and 0.1 which is 30~36%, moderate between 0.2 and 0.3 which is 9~22%, less more than 0.3 which is 1~11%, least less than 0 which is 0~5% for 10~30m、10~50m、10~70m、30~50m、30~70m、50~70m.The grades are reasonable from the distribution of research result. Spatial distribution of annual average wind shear index shows the wind shear index of Northeast China and Inner Mongolia between every layer is larger with 0.2~0.3 and more than 0.3. The wind shear index of Changtu County of Liaoning Province is the largest in the northern region which is between 0.268 to 0.467. The wind shear index is 0.2 and above in Complex mountainous area of Wufeng County of Hubei Province, Dayao County of Yunnan Province, Xiushui County of Jiangxi Province, Pingshun County of Shanxi Province. The research result show that wind shear index is greater than 0.2 accounted for 10~33%.The wind shear of wind turbine specification for the normal wind profile model(NWP) and extreme wind shear profile is 0.2, the research make advice by the results of the regions which are improper to install the wind turbine with standard configuration.Wind shear index of every month of one year is from 0 to 0.1 mostly in addition to an exception.The wind shear index of monthly variation of one year is quite different in every layer of different wind tower. Generally, monthly wind shear index of one year is relatively large in unventilated Valley and the peak of mountainous area in mountainous terrain.In the hilly area. The wind shear index is the largest in Quanjiao County, Anhui Province which is from 0.2 to 0.4. Xinjiang Mulei County is from 0.05 to 0.18 which is medium level. Inner Mongolia Shangdu County is from 0 to 0.15 which is minimum level. Wind shear index of every month every layer of 4 towers is larger in two County on Plain. Wind shear index of Liaoning Changtu county is from 0.12 to 0.6. Wind shear index of Taonan county is from 0.05 to 0.35. Wind shear index is from 0 to 0.2 except Gangcha County 1# tower 50~70m and Dayao County 2# tower. The percentage of wind shear index of every month is larger which is range from 0.1 to 0.4 in one year in the South and North China Coastal. Volatility of wind shear index is relatively larger for individual tower. Overall, wind shear index in winter is the largest in inland mountain, plateau, hilly terrain when coastal becomes large in winter. Wind shear index is relative maximum in May, June, July in the South China Coastal.Wind shear index is relative maximum in August and September in the Northern China Coastal. In addition to the seasonal variation, there is a big difference in wind shear index in the same area of the same year, due to local topography, underlying surface differences.Diurnal variation of wind shear index is followed the change of law. Wind shear index is larger at night and smaller after sunrise then to a minimum around midday due to the atmospheric boundary layer vertical mixing enhanced except the coastal areas and a special case. Diurnal variation of wind shear index is closely related with the sunrise and sunset time, vegetation cover degree and time, the heat capacity of the surrounding environment, the extent of undulating terrain, obstacle height and distance, the distance to the sea, the distance to the lake and etc. in both inland and coastal area. Wind shear index declines earlier when sunrise earlier in the day.Wind shear index rise earlier when sunset earlier in the afternoon. Wind shear index change is slower, smaller when ambient heat capacity is larger, and vice versa; The middle layer wind speed of the tower is greater with greatly undulate terrain, while middle and low layer wind shear index is larger, middle and upper layer wind shear index is smaller. It has greater impact on wind speed when obstacle height higher and closer to the wind tower, the impact should be analyzed according to the actual situation; Wind shear index is smaller, the magnitude of the change is smaller when more close to the sea, lake under the same condition.Wind farm construction, airport siting, construction of buildings, the influence of buildings and structures etc. were discussed according to wind shear index of annual average distribution, monthly and diurnal variation during the year.The rearch analyze the difference of wind shear index between calculated value according to the structural load specifications A, B two types and the measured value.The research proposed measured wind shear index average is 0.203 in Leizhou of South China Coastal which is type A class higher than the specification calculated value 0.12 of 69.2%. Measured average wind shear index is 0.132 in hilly area which is B type near to pecification value 0.15. Measured wind shear index average is 0.294 on the Northeast plain which is B type higher than the specification calculated value 0.15 of 96%.Wind speed, air pressure and wind loads above 10 m will be underestimated in Leizhou, Northeast Plain if compute wind load using wind shear index in specification which is 0.12, 0.15.Calculation formula and consistent meaning is the same between Local Air Pollutant Emission Standard GB/T3840-91 wind profile exponent and wind shear index of the researth. Village has five levels of wind profile exponent in the range of 0.07 to 0.25 in the standard. The research was first proposed the method estimating the chimneys environment mean wind speed is not accurate enough according to the county weather station wind speed and wind profile exponent of sources.The research set Jilin Taonan and Changtu County in rural areas as an example on plain. The measured annual average wind shear index of which is the range from 0.1514 to 0.4670, with an average of 0.2940, far higher than the specified values which is from 0.07 to 0.25. Measured average wind speed of air pollution chimneys environment higher than the value calculated using the specification corresponding to the same place. Among them measured wind speed is 46.3 ~ 131.4% higher than the specified formula caculation in Taonan six towers,and is 3.4 to 56.0% higher in Changtu County three towers. |
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