A Study On Influence Of Station's Environment Changes On Measuring Wind In China's Eastern Coast

With the economic development and the growing concern on green energy, large-scale engineering projects such as cross-sea bridges, wind farms and nuclear power plants are being continually carried out in China's coastal regions. None of the climate assessments of these projects hasn't involved consulting long-term wind speed series of the weather stations. However, human factors like urbanization and variations of its neighboring environment are affecting the normal fluctuation of long sequence wind speed data. Through statistical analysis and CFD simulations, this paper analyzes the characteristics of long-term changes and reasons of wind speed in coastal regions and reveals the rule of the influence of buildings on wind speed. It probes into the corrections of the influence, which provides the scientific basis for the correction of long-term wind speed series.The paper extracts not only the regular data of wind direction and speed which are observed four times per day, but also the evaluation of observed environment from the chosen 16 costal climate stations from Shandong in Eastern China to Fujian during the year of 1971 to 2007. In this way, the variation of annual mean wind speed of Eastern coastal stations are divided into three types as follows:type A's changing tendency is not obvious and the environment is kept original as it is; type B descends gently under inapparent affection of surrounding obstacles; type C descends obviously under apparent effect of the surroundings. Accordingly, tendency value of the three are 0.01 to-0.01 ms-1/(a),-0.01 to-0.03 ms-1/(a) and-0.03 to-0.12 ms-1/(a) respectively.The two conclusions based on the analysis of the influence of environment on wind speed are 1)changes of large-scale underlying surface of observation station site make wind speed of all directions decline;2) surrounding obstacles on the wind direction make its speed change remarkably and general speed decline regularly.The statistic analysis indicates that it could be an effective method to correct long-term wind speed data of type C observation station by combining statistic test and environmental changes data as while as referring to a regional standard wind speed data.By applying Computational Fluid Dynamics (CFD) theory to simulate the influence of buildings on the north side of Dongshan station in varied wind directions and speed, it shows that the relative position of buildings, angle of blowing and anemometer mast decide the building's influence on wind speed as a whole. It leads to the conclusions as follows:1)Speed of N/NNW whose direction over against the building reduce evidently, the simulation output are consistent with observed 5a mean wind speed after building was constructed. 2)Speed of NNW/NE that beside the building reduce slightly or even increase, the simulation output differ from the observed data slightly.3) Wind speed declines both in the windward and leeward side of buildings, moreover, buildings almost effect nothing when windward side is five times as high as the buildings; on the leeward side of the buildings, recovering proportion of wind speed increases logarithmically along flow line so relations of wind speed recovering proportion and leeward distance in N and NNE wind directions were built.4) Based on the fact that there's linear relationship between simulation results and input value, relations of the two in N and NNE wind directions which are easily to be affected by buildings were built to be basis of wind speed correction.5) At vertical direction, the influence range of buildings is within 6m above height of the building.Simulations under various wind directions indicates that:1)based on the fact that there's linear relationship between simulation results and input value, relations of the two in N and NNE wind directions which are easily to be affected by buildings were built to be basis of wind speed correction;2)wind speed declines both in the windward and leeward side of buildings, moreover, buildings almost effect nothing when windward side is five times as high as the buildings;3)on the leeward side of the buildings, recovering proportion of wind speed increases logarithmically along flow line so relations of wind speed recovering proportion and leeward distance in N and NNE wind directions were built.Corrections have been made on annual average wind speed in two directions after the buildings were set up by making use of the results of the simulations. Linear tendency value of N direction, which is more susceptible to buildings, varies from-0.022ms-1/a to 0.011ms-1/a, the changing tendency is approaching A instead of B, or we can say effect of buildings has been eliminated. The unobvious effect under NNE direction suggests that the correction have deviated from the wind speed in the most influential direction of the buildings, so other factors have to be taken in to consider besides buildings.By classifying observation environment and characteristics of wind speed series change, this paper discusses corrections of wind speed series and provides scientific reasons for observation environment conservation and logical use of long sequence wind speed data by employing the results of quantitative analysis on buildings' influence on wind speed through CFD simulations.