江苏沿海近地层强风风切变指数特征研究

The Wind Shear Exponent in the Near-Surface Strong Wind in the Coastal Areas of Jiangsu Province

利用江苏沿海5座测风塔长序列(连续42个月)、高时间分辨率(10 min一次)的梯度风、气温、气压等观测资料,分析不同地区、不同高度层的风切变指数变化规律,并筛选出对江苏产生较大影响的7次台风和17次寒潮天气过程,分析强风条件下的风切变指数变化特征。结果表明:(1)风切变指数随环境在0.15~0.26之间变化,风机有效风速段和15 m·s-1特征风速段的风切变指数分别平均为0.20和0.19,不同高度层之间风切变指数随高度增加而减少,随风速增大呈对数关系减少。(2)台风影响时垂直混合运动强烈,风切变指数变小,平均为0.19。台风中心经过时的风切变指数和风速具有M型变化形态,最低为0.05,加上风向剧变,易对风机叶片产生破坏。(3)寒潮影响时的风切变指数平均为0.22,小于同期平均。风速倒置现象明显,在50~100 m之间风切变指数为负值的出现概率超过8%,50 m高度处容易出现近地层的最大风速层。

In order to study the characteristics of wind shear exponent under strong wind conditions of Jiangsu Province,the long sequences(from June 1st 2009 to Nov.30th 2012,continuous 42 months),high time resolution(every 10 minutes)gradient wind speed,wind direction,temperature,pressure of 5 wind towers along the coast area are used to analyze the relationship between wind speed and altitude,the time variation of wind shear exponent and the variation law with wind speed.The 7 typhoons and 17 cold wave weather processes with great influence on Jiangsu were selected,and the variation characteristics of wind shear exponent under strong wind conditions were analyzed.The results showed that:(1)The exponential law is well fitted to the vertical variation of wind speed along the coast of Jiangsu Province.The wind shear exponent varies between 0.15 and 0.26 in different surface environments.The wind shear exponent between cut-in speed and cut-out speed of the wind turbine is 0.20,and it is 0.19 when the wind speed of 70 m is 15 m·s-1.The wind shear exponent decreases with increasing height and decreases logarithmically with increasing wind speed.(2)Due to the strong vertical mixing motion caused by the typhoon,the wind shear exponent becomes smaller,with an average of 0.19.When the typhoon center passes,the wind shear exponent and wind speed have an M-shaped variation of increasing-subtracting-re-increasing,with a minimum of 0.05,and the wind direction changes drastically,which is easy to damage the fan blades.(3)The wind shear exponent when the cold wave is affected is 0.22 on average,which is less than the average value of the same period.The wind speed inversion phenomenon is obvious,the probability between 50 m and 100 m exceeds 8%,and the maximum wind speed in the near-surface layer is prone to occur at a height of 50 m.