Numerical simulations of secondary atomization characteristics of shear-thinning kerosene gels

Owing to their unique non-Newtonian characteristics, gel propellants have become a new type of fuel with promising applications in the aerospace industry. However, the complex rheological properties and high viscosity of gels pose significant challenges for flow control in gel engines, particularly in terms of fuel atomization and combustion efficiency. Focusing primarily on kerosene gel, this study investigates the secondary atomization characteristics of shear-thinning droplets, where the volume of fluid method is employed to capture interface dynamics on adaptive grids, and the viscosity of the gel is described by a power-law model. The accuracy of the numerical model is validated by comparing it with the experimental observations of the breakup process of 1% silica kerosene gel droplets. Numerical simulations are conducted to analyze the droplet breakup processes and formation mechanisms under bag, multimode, and shear breakup. Compared to kerosene, the apparent viscosity distribution inside the kerosene gel droplets is non-uniform, and the inhibition of viscous force delays the breakup time and reduces the droplet deformation, thereby affecting the transition of the breakup mode. By varying the Weber number, We, the rheological parameters, and the density ratio, the quantitative effects of these factors on droplet deformation, centroid velocity, average viscosity, the breakup time, etc. are revealed. The results indicate that the breakup becomes more severe with increasing We number, resulting in larger deformation and a greater number of smaller droplets; the rheological parameters significantly affect the droplet breakup by altering the fluid viscosity; moreover, under the same flow condition, the higher the density ratio, the more difficult it is for the droplet to break up; however, on dimensionless scales, the effect of density ratio appears weak. Additionally, a breakup regime diagram is constructed in the We-Oh (Ohnesorge) number space for low Weber numbers. This study validates the numerical method for simulating the secondary atomization of kerosene gel propellants, providing a thorough analysis of three breakup mechanisms and the impact of key parameters on kerosene gel droplets. These insights offer a theoretical foundation for the optimization of gel propellants, aiding in the development of efficient and stable propulsion systems.