不同风场下大跨平屋盖表面锥形涡诱导的风压特性研究

Characteristics of conical vortex induced wind pressure on a large-span flat roof in different wind fields

通过平屋盖刚性模型风洞测压试验,对均匀流场和湍流场作用下平屋盖表面锥形涡诱导的风压特性进行研究。①对比不同流场下平屋盖表面锥形涡诱导的平均、脉动风压分布和脉动风压谱,发现均匀流场中的平均风吸力强劲,而湍流场中的风压低频脉动能量突出;②分析不同流场下的风压概率密度曲线,指出湍流场作用下,再附区风压概率密度曲线表现出双峰分布;且旋涡再附效应显著,这将对屋面产生巨大的破坏力矩;③分别利用点涡、兰金涡和基于兰金涡简化的Cook公式对锥形涡作用下的风压剖面进行拟合,结果表明兰金涡模型和Cook公式均适用于预测旋涡作用下的风压剖面,点涡模型则低估了实际风吸力;④在湍流场中对比了不同风向引起的风压分布,发现当来流沿屋盖对角线时,两侧旋涡强度相当,旋涡再附运动强劲,当来流偏离屋盖对角线时,在屋面靠近来流的一侧,横风向脉动加速了旋涡的旋转,增加了旋涡诱导的平均吸力;在远离来流的一侧,屋面平均、脉动吸力均减小。

Based on the wind tunnel tests,the characteristics of wind pressure induced by conical vortex on a large-span flat roof are investigated under uniform flow and turbulent flow,respectively.Firstly,the mean and fluctuating wind pressures,as well as wind pressure spectra,are compared in different flow fields.Results indicate that the mean suction on the flat roof is strong in the uniform flow,while in the turbulent field the low-frequency fluctuating energy of wind pressure is more pronounced.Next,the probability density functions of wind pressures in different flow fileds are analyzed,the bimodal distribution is observed on the curve of probability density in a separated and reattaching flow field.The vortex reattachment effect is apparent,causing overturning moment for roof-mounted items.Thirdly,wind pressure profile due to the conical vortex is fitted by the point vortex,Rankine vortex and simplified Cook expression,respectively.It is shown that the Rankine vortex and simplified Cook expression can properly describe the pressure profiles due to the conical vortex,while the point vortex underestimates the actual wind suction.Finally,pressure distributions produced by different wind directions in the turbulent flow field are compared,it is found that when the wind direction is along the diagonal of the roof,the intensity for the vortex pair is almost equal and the vortex movements are strong.When the approaching flow deviates from the diagonal,the lateral wind fluctuation accelerates the whirling of vortex on the windward side,leading to the increased the vortex induced mean suction.On the leeward side,both the mean and fluctuating suctions decrease.