Wind profiles and characteristics in thunderstorm downburst are significantly different from the regular boundary layer winds. Based on the computational fluid dynamics (CFD) commercial software, thunderstorm downburst is simulated in the 1:2 000 geometry scales, and the results are compared to the theoretical model. Effects on mean pressure coefficients of the distance from the roof to the center of the downburst are investigated by placing flat-roofs at different radial locations. Pressure coefficients and flow velocity around the roof are analyzed and compared to the results in the boundary layer winds. The results show that numerical simulations can appropriately reproduce the wind profiles and characteristics of the downburst. The pressure coefficient distribution of flat-roofs in the thunderstorm downburst is obviously different from that in the boundary layer winds. The pressure coefficient distribution depends on the distance between the flat-roof and the center of the thunderstorm down-burst. The pressure of the roof gradually changes from positive value to negative when the flat-roof is moved away from the center of the impinging jet.%下击暴流具有与常规大气边界层近地风完全不同的风场特征.基于CFD(Computational fluid dynamics)数值仿真技术,完成了几何缩尺比为1∶2 000的下击暴流过程的数值模拟,并将其风剖面的模拟结果与理论模型进行了对比.在此基础上,研究在下击暴流作用下,将大跨平屋面置于距下击暴流中心不同径向位置时,屋面平均风压系数和速度场的分布规律,并与大气边界层风场中平屋面的风荷载特性进行了对比.结果表明:数值模拟方法能够较好地再现下击暴流的风场特性；下击暴流风场中平屋面风压分布规律明显区别于大气边界层风场中的风压特性；平屋面风压分布特性与其距下击暴流中心的距离密切相关,随着平屋面逐渐远离下击暴流中心,屋面所承受的压力逐渐由正压转为负压.
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