Numerical analysis of air entrapment during water droplet impact on a substrate

Abstract

As a liquid droplet impact on a substrate, it spreads flattens, and air may become trapped between the droplet and the substrate. This trapped air first evolves into an air film, which passes through many stages before eventually becoming an air bubble through retraction, contraction, toroid creation, pinching off, and so forth. The droplet cools while spreading across the substrate and finally freezes to create a splat. In most thermal spray coating applications, this phenomena is seen in the individual droplet solidification. The major purpose of this research is to develop an OpenFOAM solution that can model the effect of molten droplets on solid surfaces using free surface evolution. The PIMPLE algorithm, which is used in this solution, combines the PISO (Pressure Implicit with Splitting of Operators) and SIMPLE (Semi Implicit Method for Pressure-Linked Equations) approaches. In this approach, pressure–velocity equations are resolved, and the continuous surface flow model is used to simulate the surface tension force. Furthermore, the solution incorporates the dynamic contact angle. An enthalpy-based formulation that takes solidification into account is used to simulate the energy equation. The solver is validated with the aid of the available experimental results. Hydrodynamics can be used to properly simulate the various stages of air entrapment.