Numerical Simulation Of Binary Droplet Collisions In Gaseous Environment

Binary droplet collision dynamics are widely applied in various fields related to atomization,such as spray combustion,spray drying,and drug spraying,and play a key role in the development of technologies such as steam separators,3Dprinting,and microfluidics.The research on binary Newtonian droplet collisions mainly focuses on the establishment of collision models at low and medium We numbers(We=0 ? 200),while the research on binary non-Newtonian droplet collisions has not been fully developed due to its complicated rheological properties.Based on the OpenFOAM computing platform,combined with CLSVOF(Coupled Level-Set and Volume of Fluid method)and AMR(Adaptive Mesh Refinement)technology,the CLSVOFDy MFoam solver was established.The specific research work can be divided into the following two parts:Firstly,binary Newtonian droplet collisions were simulated numerically under high We number conditions.The results of binary equal-sized droplet collisions at high We number(We=210 ? 1520)showed that:(1),with the increased of We number,the collision characteristics of fingering,splattering at the receding phase,breakup and prompt splattering can be observed.(2),compared with binary equal-sized droplet collisions,at high Weber number(We=210 ? 810),binary unequal-sized droplet collided and deformed into a hole-like structure.As the We number increased,the movement of the droplets changed from small droplet penetrating into the large droplet and into large droplet penetrating into the small droplet.The rim of the droplets showed different expansion behaviors and the breaking time was advanced.Different breakup behavior of the rim can be observed,for example,the petal-shaped rim extended downward and broke,the downwardly spreading rim broke and formed a large area of splashing satellite droplets,the upwardly expanding rim broke and the edge formed a wavy structure,etc.(3),by discussing the effect of the size ratio(?)and initial velocity on binary unequal-sized droplet collisions,we can find that the collision dynamics of binary unequal-sized droplets were mainly controlled by large droplet.Secondly,based on the non-Newtonian viscosity model,binary non-Newtonian droplet collisions were simulated numerically.The effect of surface tension on binary non-Newtonian droplet collisions was discussed in detail,and the collision behaviors of Newtonian and non-Newtonian fluids were compared.Results showed that:(1),the surface tension promoted the drainage process,causing the droplets to merge faster.As the surface tension decreased,the We number increased.There was an obvious time delay in the process of the droplets reaching maximum deformation and recovering to a stable spherical droplet.(2),compared with the Newtonian fluid,the non-Newtonian effect can promote the maximum deformation of the droplets.Under the action of viscous dissipation,the initial merging speed of the droplets slowed down,and eventually coalesced permanently without separation.