气相中双液滴正碰过程数值模拟研究

液滴碰撞现象普遍存在于动力装置燃烧室喷嘴的下游区域,影响燃料的雾化性能。为了揭示相同直径的双液滴中心碰撞机理,求解了轴对称坐标系下的N-S方程,采用VOF(Volume of Fluid)方法捕捉液滴碰撞过程中气液自由表面的演化规律。利用Qian等提供的实验结果对计算模型进行数值校验,验证了模型的准确性。在此基础上,研究了环境压强对液滴碰撞反弹后不同结果(分离和融合)的影响,分析了环境压强和Weber数对液滴碰撞分离的影响。结果表明,液滴在碰撞反弹后的状态(分离或融合)是由液滴间气膜压强与环境气动阻力共同作用的结果,环境压强对液滴碰撞分离过程基本没有影响;Weber数越大,碰撞过程中变形的幅度越大。

Numerical simulation of head-on binary collision of droplets in gas phase environment

The phenomena of droplet collision not only exist widely in the downstream region of ejection nozzles in the combustion chambers of power equipments,but also they will affect the atomization characteristics of fuel.In order to reveal the binary collision mechanism of droplets with equal diameters,the Navier-Stokes equations are firstly solved in the axisymmetric coordinates and the method of VOF (Volume of Fluid) is utilized to track the evolution disciplines of the gas-liquid free surface during the process of droplet collision.Then,veracity of the numerical models is validated with the experimental results of Qian.Effects of ambient pressure on different results (separation and coalescence) after droplet bouncing are investigated,and effects of ambient pressure and Weber number on separation of two droplets after collision are also analyzed.Results show that states (separation and coalescence) of droplets after collision and rebound are determined by the pressure of gaseous film between droplets and gaseous dynamic resistance together.Moreover,the separation process of two droplets after collision is independent of the ambient pressure,and the higher Weber number of droplets leads to more serious deformation.