露天堆场防风抑尘网临界孔隙率的数值模拟

应用Fluent6.3对防风抑尘网及料堆周围流场进行数值模拟,通过研究不同孔隙率抑尘网与料堆周围湍流特性及料堆表面剪切力分布规律,确定了临界孔隙率.结果显示:高孔隙率(0.3、0.4、0.6)流动状态与无网工况一致,来流风沿迎风面贴附向上,风速逐渐增大,堆顶达到最大;低孔隙率(0、0.2)流态与无网迥异,迎风面处于涡旋中,风速向下,孔隙率为0时涡旋中心高于堆顶3m,孔隙率为0.2时涡旋中心位于堆高2/3处.孔隙率30.3时,料堆各表面剪切力变化趋势一致,与无网工况来流风同向,最大剪切力出现在堆顶.孔隙率为0.2时,作为最大起尘量的迎风面,其表面剪切力随高度先增大后减小,最大剪切力处于堆高3/5处.孔隙率为0.25时,湍流结构和剪切力分布发生突变,迎风面为贴附和涡旋复合流动,表面剪切力最小.据此确定来流风速6m/s,运用该几何模型时,临界孔隙率为0.25.

Numerical simulation for critical porosity of porous fences used to shelter open storage piles

The flow field around the open storage piles behind a porous fence was numerically simulated by the software Fluent 6.3. The critical porosity was determined based on the datas obtained from the simulation of flow fields for the porous fence with different porosities and the shear stress distribution above the windward side, flat top surface and leeward side of the pile. As a result, the flow structures at high porosities (0.3,0.4,0.6) were similar to that of the unfenced condition. The air velocity was higher from the ground to the top of the windward surface and the velocities were all positive. At low porosities (0,0.2), however, the flow structure differed strongly with that of the high porosities. Large-scale vortices were formed between the fence and the storage pile, thus the velocity of the air above the windward was negative. For the fence with e=0, the height of vortex center was higher 3m than the height of the pile and for the fence with e=0.2, the vortex center located at the 2/3 height of the windward surface. In addition, the shear stress distribution was similar to that of the unfenced condition when the fence porosity was exceeded 0.3and the shear stress increased with the increasing porosities. For the e=0.2 porous fence, however, as the height of the pile increased, the shear stress increased, then decreased and the maximum shear stress was at the 3/5height of the pile. When the fence porosity was 0.25, both vortex and attached flow were formed above the windward surface and the shear stress of the pile was to be the least. Thus the porosity e=0.25 below or above which turbulence structures and the shear stress distributions differed strongly was determined to be the critical porosity in this study. The method studying aerodynamics microscopic characteristics around the piles provides a new idea for the porous fence investigation.