NUMERICAL SIMULATION OF OLDROYD-B VISCOELASTIC DROPLET COLLISION

The complex rheological properties make the atomization process of gel propellant difficult, which restricts its development. The addition of polymer gelling agent makes the gel propellant viscoelastic, so that viscoelastic droplets will be generated during atomization. Therefore, in order to further understand the atomization mechanism of gel propellant and improve the atomization performance of gel propellant , to carry out numerical simulation research on the collision behavior of viscoelastic droplets. Aiming at the droplet collision phenomenon in the atomization process of gel propellant, considering the viscoelastic effect of fluid, volume of fluid (VOF), adaptive mesh refinement (AMR), and log-conformation transformation were adopted. The Oldroyd-B constitutive model was used to describe the viscoelasticity of droplets, and a direct numerical simulation of the collision process of two viscoelastic droplets of equal volume was carried out. The head-on collision process of viscoelastic droplets is mainly concerned. The effect of relaxation time, viscosity ratio, Weber number on the head-on collision behavior was studied, the energy evolution of the droplet coalescence process under different physical properties was also calculated. In addition, the droplet collision behavior under different eccentricity was observed. By changing the collision velocity, the collision results of merging and bouncing are obtained. The results show that increasing the relaxation time is beneficial to the extrusion and retraction process of the coalesced droplet, and delaying the process of the droplet deformation, this is different from the results obtained by Newtonian fluids. Increasing the viscosity ratio can hinder the oscillation behavior of the coalesced droplet. As the eccentricity of the collision increases, extension and rotation occur, and the extensional distance increases with the degree of eccentricity. When the eccentricity decreases, the kinetic energy dissipation rate increases, and more kinetic energy is dissipated.