有蒸发稀液雾冷态射流的大涡模拟研究

Large Eddy Simulation of Cold Evaporating Dilute Sprays

关键词:  稀液雾  大涡模拟  回流区  液滴蒸发  液滴弥散 

Key words:  Dilute spray  Large eddy simulation  Recirculation zone  Droplet evaporation  Droplet dispersion

摘要:

为研究气相湍流场中液滴弥散和蒸发过程的特点和影响因素,加深对气液耦合作用的认知,用欧拉-拉格朗日相结合的办法数值模拟了稀液雾冷态受限射流和自由射流。欧拉坐标系下的气相湍流场使用大涡模拟技术模拟,离散液相则使用拉格朗日颗粒轨道模型进行描述,考虑相间质量、动量、能量交换,采用相平衡蒸发模型模拟液相的蒸发效应。模拟得到的液相速度场、粒径分布和质量流率等均和实验数据较好吻合。有回流的受限射流中初始惯性对Stokes数大的液滴弥散影响较大,而Stokes数在1附近的小液滴弥散更受气相流场结构影响。液雾单位体积蒸发速率和液滴弥散分布密切相关。自由射流中液滴受初始惯性和受气相流场作用大体一致,大小液滴的弥散分布基本满足自相似性。 

Abstract:

To study the characteristics and influencing factors of droplet dispersion and evaporation in gas turbulent flows and to deepen the awareness of the gas-liquid couple, numerical simulations of the cold evaporating dilute sprays were conducted in the Eulerian-Lagrangian framework. The gas turbulent flow in Eulerian framework was simulated using large-eddy simulation while the discrete liquid phase was described using the Lagrangian particle trajectory model, considering interphase mass, momentum, and energy stransfer. And the equilibrium evaporation model was adopted to describe the evaporation effect. The simulation result of droplet velocity field, particle size distribution and mass flow rate are in good agreement with experimental data. In the confined spray with recirculation zone, droplets with big stokes number are affected by the initial inertia obviously while small droplets with stokes number around ‘one’ are controlled more by the gas structures, and the evaporation rate in unit volume is closely related to the droplet dispersion. In the free spray case, big and small droplet dispersion are in consistent and the droplet velocity field is almost self-similar. 