颗粒在大涡结构中的弥散

气相采用大涡模拟方法,颗粒相采用轨道模型研究了三维后台阶气粒两相湍流流动的大尺度涡结构的瞬时演变过程以及颗粒的瞬时弥散规律.比较了不同入流速度的颗粒在大涡结构中的瞬时弥散特性,尤其研究了高速释放大颗粒的弥散特性.三维流动中大尺度涡结构具有明显的脱离、发展、合并和破碎过程.小颗粒的分布受大涡结构的控制,其空间的弥散过程与流体 大涡结构的空间发展相一致,但是由于三维流动中大涡边缘和中心区的压力差,颗粒在大尺度 涡的边缘出现密集.而大颗粒在流场中的分布受其惯性控制,对气相的涡结构不敏感.高速释放到流场中的大颗粒受惯性影响最大,保持在其原有动量方向上运动.

Particle dispersion in large eddy structures

Gas-particle two-phase turbulent flow over a backward-facing step is studied by large eddy simu-lation coupling with Lagrangian tracking model.The three dimensional large scale structures are reproduced.Characteristics of particles dispersion in the evolution of large eddy structures are then studied.Dispersion ofparticles with different inflow velocities are compared with each other.It is shown that large scale structuresseparate,develop,amalgamate and break up in three-dimensional flow.The dispersion process of small particlesis dominated by the large eddy structures.Thus their distribution can trace the large eddy structures spatially.Due to the difference of pressure between the edge and the center of a large eddy structure,particles tendto congregate at the edge of large eddies.In contrast,the distribution of large particles mainly governed byinteria are relatively insensitive to large eddy.With high inflow velocity,large particles keep their motion inthe direction of initial momentum.