实测下击暴流风场特性分析

Analysis of wind field characteristics of measured downburst

目前下击暴流风场特性的研究大多是围绕风速模型和部分风场特性展开,较少涉及风场特性与平均风速之间的关系、不同风场特性之间的相关性以及与大地边界层近地风特性的比较研究。基于下击暴流实测风速数据,运用滑移平均法提取下击暴流的时变平均风速,进而获得脉动风速。在此基础上,研究下击暴流的紊流度、紊流积分尺度和阵风因子的特性,并分析3种特性与平均风速的关系以及3种特性之间的相关性。结果表明:下击暴流的紊流度、紊流积分尺度以及阵风因子均大于相应场地类别下相同高度处大气边界层近地风的对应风场;下击暴流的紊流度与平均风速之间、紊流积分尺度和紊流度之间均存在负相关性,而紊流积分尺度与平均风速之间、阵风因子与紊流度之间则都表现为正相关;低矮建筑的抗风设计应重点考虑下击暴流脉动成分的影响,而高层建筑和高耸结构的抗风设计应重点关注下击暴流气流涡旋的威胁;相比大气边界层近地风,下击暴流容易产生更大的瞬时极值风速,对工程结构威胁更大。

At present,most of the studies on the wind field characteristics of downburst mainly focus on the wind speed model and partial wind field characteristics.Few studies on the relationship between wind field characteristics and mean wind speed,the correlation between different wind field characteristics or the comparison with the boundary layer surface wind characteristics are carried out.Based on the measured wind speed data of downburst,the time-varying mean wind speed of downburst is extracted by utilizing the moving average method,and then the fluctuating wind speed is obtained.On this basis,the characteristics of turbulence intensity,turbulence integral scale and gust factor of downburst are studied.The relationships between the above three characteristics and mean wind speed,as well as the correlations among the above three characteristics are analyzed.The results show that:1)the turbulence intensity,turbulence integral scale and gust factor of downburst are greater than the corresponding wind field characteristic of atmospheric boundary layer surface wind at the same height under the corresponding site category;2)there is a negative correlation between the turbulence intensity of downburst and the average wind speed,as well as between the turbulence integral scale and the turbulence intensity while there is a positive correlation between the turbulence integral scale and the average wind speed,as well as between gust factor and turbulence intensity;3)the wind resistance design for low-rise buildings should focus on the influence of fluctuating components of downburst,while the threat of airflow vortexes of downburst should be paid more attention for high-rise buildings and high-rise structures;4)compared with the atmospheric boundary layer surface wind,downburst is prone to produce larger instantaneous extreme wind speed,which could pose greater threats to engineering structures.