不同表面结构叶片叶轮对搅拌流场特性的影响

Influence of vane impeller with different surface structure on characteristics of stirred flow field

为了提高流体介质的湍流强度和混合效率,将搅拌机的叶片表面设计为台阶状,将常规叶片叶轮和台阶式叶片叶轮置于圆柱直筒内,通过速度场分布、冷热水混合以及固液混合分析,进行初步的模型对比验证,再将2种形式的叶片叶轮应用至实际高效沉淀池,进行1∶1仿真计算.结果表明:台阶式叶片的表面边界层区域能够产生更为剧烈的湍流结构,在每级台阶的迎水面前方均存在回流旋涡,其流态特性极为复杂,有利于促进局部的混合反应;伴随着大量能量输入,各相介质受到台阶面的冲击挤压作用,使得冷热水和固液两相的混合效果更为均匀,这一效应在低转速(60 r/min)的模拟中表现得尤为显著;在实际高效沉淀池的仿真中,56 r/min转速下,采用台阶式叶片时,絮凝区流场的平均流速为0.152 m/s,采用常规叶片时平均流速为0.137 m/s,且台阶式叶片的湍流动能耗散要明显高于后者.因此,在转速较低的应用场景中,台阶式叶片的混合搅拌效果要明显优于常规叶片,研究结果对优化混凝工艺具有积极的意义,为新式搅拌叶轮的开发提供了一种设计思路.

To enhance the turbulence intensity and mixing efficiency of the fluid medium,the surface of the agitator′s blades was designed with a step-like structure.The conventional blade impeller and the stepped blade impeller were placed in the cylindrical cylinder,and the preliminary model comparison and verification were carried out through velocity field distribution,hot and cold water mixing and solid-liquid mixing analysis.Then the two types of blade impeller were applied to the actual high-efficiency sedimentation tank,and the simulation was carried out through 1∶1.The results show that boundary layer region of the stepped blade can produce more violent turbulent structure,and there are reflux vortices in front of the facing water of each step,whose flow characteristics are extremely complex,which is conducive to promoting the local mixed reaction.With a large amount of energy input,each phase medium is affected by the impact and extrusion of the step surface,which makes the mixing effect of hot and cold water and solid-liquid phase more uniform.This effect is particularly significant in the simulation of low speed(60 r/min).In the simulation of the actual high efficiency sedimentation tank,at 56 r/min,the average flow velocity of the flow field in the flocculation zone is 0.152 m/s when the stepped blade is used,and the average flow velocity is 0.137 m/s when the conventional blade is used,and the turbulent kinetic energy dissipation of the stepped blade is significantly higher than the latter.Therefore,in the application scenario of low rotational speed,the mixing effect of stepped blade is obviously better than that of conventional blade.The research results have positive significance for the optimization of coagulation process,and provide a design idea for the development of new type stirring impeller.