露天堆场防风抑尘网的动力学数值模拟

开放性露天堆场的散尘是大气颗粒物的重要来源. 来流空气在棱形物料堆的上部绕流,使其表面的空气流动结构逐点不同,而料堆表面的空气动力学结构又决定着堆场的散尘机理及散尘量. 分析了典型单一棱形料堆周围空气湍流结构,并应用三维标准k-ε紊流模型对其流场进行了数值模拟；计算了来流方向抑尘网前后不同断面处风速的垂直分布；分析了不同孔隙率(0、0.2、0.3、0.4、0.5、0.6和1.0)抑尘网后料堆迎风面和背风面沿高度方向、平顶面沿水平方向的剪切应力特性和分布规律. 结果表明:抑尘网前3倍网高距离处的风速较无网工况(孔隙率为1.0)略有减小,降幅随孔隙率增大而减小, 孔隙率为0时最大降幅为5.1%；网前2倍网高距离处与抑尘网之间区域的风速廓线与无网工况相差甚远,孔隙率为0时近网区域风速最高降幅达92.8%. 抑尘网和料堆迎风面之间区域,从地面至网顶高度,不同孔隙率抑尘网工况下的风速均较无网工况小,最小处为无网工况风速的18.5%；抑尘网以上区域的风速较无网工况的大,最大处为无网工况风速的128.0%,并且差距随抑尘网孔隙率的减小而增大. 料堆剪切力分布显示,其迎风面和平顶面为主要散尘面,背风面被涡旋卷起的扬尘量较前两者小得多. 防风抑尘网的设置改变了料堆周围空气的流动结构和受力分布,对不同孔隙率的抑尘网数值模拟结果可知,0.2和0.3为最佳孔隙率. 

Aerodynamic Numerical Simulation of Turbulent Fields behind Porous Fences in Open Storage Piles

Dust emissions from open storage piles constitute a significant fraction of atmospheric particulates, and wind-blown dust emissions cause heavy air pollution in addition to material losses. Each surface shows a different air floating structure when the air stream flows over a prismatic material stack. The principle and quantity of the resulting dust emissions depends on the aerodynamic characteristics of all surfaces. Static flow fields were numerically simulated using the standard k-ε turbulence model based on the turbulence structure around a typical prismatic material stack in open yards. The vertical distribution of the air velocity at various cross sections around the fence was calculated. The shear stress characteristics and distribution on the windward side, flat-top surface and leeward side of the stack were analyzed according to the flow field data for fences with different porosities (0,0.2,0.3,0.4,0.5,0.6 and 1.0). The results indicated that the air velocity was slightly reduced at the cross-section in front of the fence with distances of three times the height of the fence, which implied that the porous fence had little influence on flow field in the region. The highest reduction rate of air velocity was 5.1%. Beyond the location in front of the fence with distance of two times the height of the fence, the velocity profile significantly differed from the unfenced conditions until approaching the fence. Air velocities decreased considerably near the fence, with the highest reduction rate 92.8%. In the region behind the fence, velocity was lower from the ground to the top of fence. The minimum wind speed was 18.5% of that in the unfenced condition. In contrast, the velocity was greater above the fence, to a maximum of 128.0% of the unfenced conditions. Furthermore, the speed difference increased with decreasing porosity. The dust emissions from each surface of the pile varied differently. Since the leeward side was always in the backflow region, the dust emissions from it were much lower than those from the windward and flat-top surfaces. The analysis results showed that the porous fence changed the air flow fields' characteristics and aerodynamic structure around the storage piles. The fence with porosity 0.2 and 0.3 was determined to be the optimum by simulating the air flow fields behind the porous fence with porosity of 0,0.2,0.3,0.4,0.5 and 0.6.