下击暴流作用下坡地风场特性研究

下击暴流多发生于山地丘陵地区，而目前对于下击暴流的研究多集中在平地地形的稳态风场。为研究坡地地形对下击暴流风场特性的影响，采用冲击射流物理试验与大涡模拟（Large eddy simulation，LES）方法对平地以及三个不同坡度的坡地风场进行了试验测试与数值模拟。结果表明：大涡模拟捕捉到了风场的瞬态变化特征，环涡结构在首次越过山坡时，在坡顶檐口位置产生下击暴流风场整个生命周期中的最大风速。坡地地形除檐口位置具有显著加速效应外，其他位置未发现风速增大效应。与平地风场相比，檐口位置水平风速与竖向风速都有所增大，且近地面水平风速加速因子Mt达到1.3左右。近地面湍流度增大较为明显的区域为起坡位置及坡后位置，坡中及檐口位置加速效应较小。檐口位置湍流度加速因子随坡度的增大而略有增加。
Abstract：Downburst often occurs in the mountainous and hilly areas.At present,the research of downburst mainly concentrates on the steady wind field in flat terrain.To investigate the effects of slope terrain on downburst wind field,an impinging jet physical experiment and the large eddy simulation (LES) were used to test and simulate the wind field in flat and three different gradient slopes.The results indicate that the large eddy simulation capture the transient characteristics of wind field,and the maximum wind speed of the wind field during the whole life cycle of downburst appears when the vortex structure first arriving the crest of the slope.Except the crest of the slope has significant speed-up effect,other positions were not found this effect.Compared with the wind field on flat terrain,both horizontal and vertical wind speed have increased,and the wind speed-up factor,Mt,near the ground reached about 1.3.The position where turbulence intensity increases obviously including the foot of the slope and the area behind the crest,and other positions do not have the obvious increasing effect.With the increasing of the gradients,the amplification factor of turbulence intensity at the crest increases slightly. 