Wind Field Characteristics of Snow-Covered Low-Rise Building Roof Based on PIV Experiments
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摘要:
为研究屋盖积雪对低矮平屋面风场特性的干扰影响，基于风吹雪风洞试验，通过3D打印获得平屋面的3D积雪形态，并以无积雪模型作为对照，系统地开展了PIV （particle image velocimetry）风洞试验，并结合LES （large eddy simulation）方法，研究了6组平屋面建筑有无积雪时的流场分布特性. 试验研究表明：当无积雪时，来流在屋面前缘处分离后能形成典型的分离泡流动，分离泡内速度场存在明显逆流现象；当有积雪时，屋面上方的逆流减弱甚至消失，积雪显著地加快了流经屋面附近流场的速度，其最大速度增量约为0.6，同时，流线分布更贴合模型壁面，速度梯度增大，也相对增大了涡量值；积雪会使得屋面上方整体的时均湍动能和切应力均减小，但对屋面迎风区域的平均和脉动风压均有增大作用，其增大比值约为15%和20%. 通过该研究可进一步对低矮建筑的风雪荷载作用机理展开分析，为屋盖结构的抗风雪设计提供参考.
Abstract:To investigate the influence of snowdrifts on the flow field above low-rise building roof, the distributions of flow field above six different low-rise building roofs with or without snowdrifts were systematically analyzed through particle image velocimetry (PIV) experiments in wind tunnel combined with large eddy simulation (LES), where the tested models with snowdrifts were obtained by 3D printing based on the results of blowing snow experiments. The results indicate that a typical separation bubble can be formed above the no-snow roof when the approaching flow is separated at the leading edge, in which the obvious inverse flow can be observed. However, when there are snowdrifts on the roof, the backflow near the roof is weakened or even disappeared, which remarkably accelerates the flow velocity near the roof, and the maximum speed increment is about 0.6. Concurrently, the distributions of streamlines for snowdrift cases are closer to the building surface and have a larger velocity gradient, and hence the vorticity is also increased. The further numerical research on the turbulent characteristic above the building roof based on LES indicates that the turbulent kinetic energy and turbulence shear stresses above the snowdrift roof are also significantly smaller than their counterparts above the no-snow roof. However, the snowdrift increases the mean and fluctuating wind pressures in the windward region of the roof, and the reduction ratio is about 15% and 20%, respectively. Through this study, the mechanism of wind and snow load on low-rise buildings can be further analyzed, which can provide a reference for the wind-and-snow resistant design of roof structures.
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Key words:
- low-rise building /
- PIV experiment /
- snowdrift on roof /
- flow characteristic /
- large-eddy simulation.
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图 4 模型 2有/无积雪情况的时均速度分布
Figure 4. Distributions of the mean streamwise and vertical velocities for model 2 with and without snowdrifts
图 5 有/无积雪时屋面特定路径上的速度对比
Figure 5. Comparison of streamwise velocities atthe specific route for all cases
图 11 有无积雪时湍动能和湍流应力分布对比
Figure 11. Comparison in distributions of turbulent kinetic energy (k) and turbulent shear stresses (
${u}_1{w}_1$ )with and without snowdrifts表 1 PIV试验工况
Table 1. PIV experiment cases
模型编号 L/H W/H 有无积雪 模型 1 1.0 2.0 有/无 模型 2 2.0 2.0 有/无 模型 3 3.0 2.0 有/无 模型 4 4.0 2.0 有/无 模型 5 2.0 1.0 有/无 模型 6 2.0 3.0 有/无 
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表 2 边界条件和求解设置
Table 2. Boundary conditions and solution settings
计算条件 边界条件及求解设置 入口 速度入口，式（1） 出口 压力出口 两侧和顶部 对称边界 建筑和地表 无剪切壁面 求解算法 分裂算子的压力-隐式方法 动量项离散 有界中心差分 时间步长/s 0.000 2 总物理时间/s 10
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