Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows

TL;DR

This paper reveals an additional interfacial force in lattice Boltzmann models for incompressible multiphase flows, affecting droplet dynamics and flow behavior, and highlights the inconsistency in the recovered momentum equation.

Contribution

It identifies an overlooked interfacial force in existing lattice Boltzmann models and investigates its effects through numerical simulations.

Findings

Additional force influences droplet breakup and secondary droplet formation.

The force increases droplet falling velocity and reduces stretching.

Models need correction for accurate multiphase flow simulation.

Abstract

The existing lattice Boltzmann models for incompressible multiphase flows are mostly constructed with two distribution functions, one is the order parameter distribution function, which is used to track the interface between different phases, and the other is the pressure distribution function for solving the velocity field. In this brief report, it is shown that in these models the recovered momentum equation is inconsistent with the target one: an additional interfacial force is included in the recovered momentum equation. The effects of the additional force are investigated by numerical simulations of droplet splashing on a thin liquid film and falling droplet under gravity. In the former test, it is found that the formation and evolution of secondary droplets are greatly affected, while in the latter the additional force is found to increase the falling velocity and limit the stretch of the droplet.