Jet characteristics of multiple oil droplets impinging process under the influence of micro-bubbles

In the process of oil–gas micro-lubrication, the lubricant oil liquids are disturbed by high-speed airflow and are prone to forming oil droplets containing micro-bubbles. Micro-bubbles have a significant influence on the kinetic characteristics of successive/synchronous oil droplet impingement on an oil film and its oil film formation mechanism. Numerical simulations of successive/synchronous oil droplet impinging oil film behavior are based on the coupled level set-volume fraction (CLSVOF) method. The effect of micro-bubbles on the flow dynamics characteristics of the successive/synchronous impinge oil film of double oil droplets is investigated. To investigate the mechanism of jet formation during the impingement process, the law of micro-bubbles influences the formation process of the central and neck jets and their morphology is analyzed. The results show that when micro-bubbles exist, the oil droplet impingement process produces the central jet phenomenon. During successive impingements, the micro-bubble is in the pilot or trailing oil droplet, respectively, and there is a large difference in the jet mechanism generated by these two cases. The energy loss in the successive impingement process is larger when the micro-bubble is inside the pilot oil droplet. The central jet hurts the velocity discontinuity effect of the fluid inside the oil film and plays an inhibiting role in the growth of the crown splash. When the micro-bubble is only within the trailing oil droplet, then the surface tension effect excited by the impingement between the subsequent oil droplet and the flat fluid surface inside the impingement crater will cause a transient sudden reduction in the inner diameter size of the crown splash. During the synchronous impingement, the symmetric micro-bubble impinge mode has a positive effect on both the final horizontal expansion inner diameter of the crown splash and its vertical jet height enhancement. The research method of numerical simulation is used in this study. Seven sets of impingement models under the influence of different micro-bubbles are systematically studied and analyzed under the premise of verifying the feasibility of the numerical method. The results of this study can provide theoretical references for the study of the impingement kinetic behavior and film-forming flow mechanism of highly viscous droplets.