Abstract
A tunable surface tension pseudo-potential lattice Boltzmann method (LBM) is applied to study a droplet splashing on a thin film over a rough surface. Our study focuses on the crown evolution processes influenced by various roughness parameters, including the protrusion height and the distance between two protrusions. The total kinetic energy of the crown is introduced to study the evolution process. The results indicate that more kinetic energy is consumed in the collision process and that the crown has a shorter dimensionless height in the case of a rough surface than with a flat surface. A threshold dimensionless protrusion height exists at which the energy consumption is minimized and the crown height is maximized. The dimensionless distance between two protrusions may affect the symmetry of the liquid crown but does not influence the kinetic energy consumed in the impact process. Neither the protrusion height nor the distance between two protrusions has a significant effect on the crown radius evolution process. This study shows that the proposed LBM pseudo-potential model is an effective tool for predicting the process of a droplet impacting a thin film in the presence of complex boundaries.
Highlights
The impact of droplets on thin liquid films is widely encountered in natural and industrial scenarios, including engine spray, inkjet printing, and pesticide spraying
The results indicate that more kinetic energy is consumed in the collision process and that the crown has a shorter dimensionless height in the case of a rough surface than with a flat surface
The process of a droplet impacting a thin film above a rough surface has been simulated using a tunable surface tension pseudopotential lattice Boltzmann method (LBM)
Summary
The impact of droplets on thin liquid films is widely encountered in natural and industrial scenarios, including engine spray, inkjet printing, and pesticide spraying. The multi-relaxation time collision operator was applied to this model by Mukherjee and Abraham, who studied the influence of the density ratio, viscosity ratio, and liquid film thickness This model has been extended to three dimensions by Cheng and Luo, allowing the effects of the moving liquid film on crown evolution to be analyzed. A high-density-ratio pseudo-potential model with thermodynamic consistency and tunable surface tension was proposed by Li and Luo, allowing a droplet splashing on a liquid film to be simulated under various Reynolds and Weber numbers. The present authors proposed a modified axisymmetric pseudo-potential model and analyzed the crown formation and break up processes from an energy perspective Both the phase-field and pseudo-potential LB models have been used to study droplets impacting on thin films, to the best of our knowledge, little research has focused on the surface geometry in the process of a droplet impacting a stationary liquid film.
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