湍流分离流中颗粒的扩散机制

Particles diffusion mechanism in turbulent separation flow

后台阶流动包含分离流重要的流动特性,采取欧拉-拉格朗日耦合算法对后台阶分离流动中颗粒扩散运动进行数值研究.气相场采取大涡模拟方法,亚格子模式基于标准的Smagorinsky模式,颗粒相运动采取轨道法模拟.计算所得气相的流向平均速度和平均脉动速度与实验结果吻合较好,验证了模型和方法的正确性.基于此,数值分析后台阶两相流动的特性以及流场涡结构的发展和演化过程.结果表明:两相流中颗粒的扩散特性既受到颗粒粒径的影响,又与颗粒和涡结构的相互作用时间有关.后台阶流场中增加结构物时,流场涡结构发生变化,即与扰动源保持一定距离后,涡数量增多,流场中颗粒分布不均匀,较多颗粒聚集在涡的外缘.

Back-facing step flow contains important characteristics of a separation flow. Based on this, a numerical ,simulation on particles diffusion mechanism in turbulent separation flow was conducted by Euler-Lagrangian coupled method. The gas phase governing equations were solved by large eddy simulation method and the subscale grid model was solved by Smagorinsky model. The particle phase was tracked with Lagrangian method. The accuracy of the solver was tested by comparing the simulation results with the experiment data. Based on this solver, the characteristics of the two phase flow, and the developing and evolutional process of vortex were numerically analyzed. The results showed that the diffusion of particles was related to particle＇s diameter, the interaction time between particles and vortex structures. The structure of vortex changed when an obstacle was added to the flow field. The number of vortex increased at a certain distance away from the obstacle. The particles concentrate at the edge of the vortex and the distribution of particles were nonuniform in the flow field.