Progress in the dynamics liquid film dynamics

Interfacial flow is a transport phenomenon that occurs at the interface between different phases in a multiphase fluid system (such as gas-liquid, liquid-liquid, or solid-liquid). Due to the combined effects of the interactions between gas, liquid, or solid substrates, as well as factors such as interfacial tension, viscosity, density differences, external pressure, and temperature, interfacial flow exhibits complex flow instability behaviors and can form interesting spreading patterns, playing a crucial role in processes like spin coating, emulsion manufacturing, and bubble coalescence. In fluid dynamics, the film flow with a free surface is a classic and important research topic and one of the main objects of study in the research of flow stability. From the perspective of engineering applications, in-depth exploration of thin film flow stability holds paramount significance for understanding microscale liquid behavior, addressing nanoscale lubrication challenges, and developing efficient micro/nano-scale heat transfer technologies. Against the above background, this article provides a detailed review of the theoretical analysis, numerical simulations, and experimental methods related to liquid film flow over the past 20 years. It expounds on the mechanisms of action of physical quantities such as viscosity, surface tension, pressure, and gravity on the flow stability and nonlinear spreading behavior of liquid films. It gives a fluid mechanics explanation for various liquid film flow phenomena in daily life and also offers a prospect for the future research directions of liquid film flow.