Gas-liquid-solid (GLS) three-phase interactions play a significant role in many essential areas but present many critical challenges for computational fluid dynamics methods to study. In this paper, we present a GLS contact condition-enforced immersed boundary method (IBM) for simulating multiphase flow problems with curved and moving boundaries on simple Cartesian meshes. Together with the phase field conditions, a GLS contact condition is introduced in the Cahn-Hillard model and then dealt with by the IBM to effectively eliminate mass leakage at the solid boundary. Both the phase field and contact conditions are consistently enforced by proposing a second-order moving-least-squares (MLS)-based IBM. In addition, the velocity correction IBM is applied to enforce the no-slip condition at the solid surface. The flow field is solved by using the multiphase lattice Boltzmann flux solver (MLBFS), which is suitable for multiphase flows at large density ratios. The performance of the present method is well examined through many challenging benchmark tests, including both steady and unsteady GLS problems, such as droplet spreading and impacting circular solid surfaces with different wettabilities. The good agreements with theoretical and available numerical data published in the literature show that the present GLS contact condition-enforced IB-MLBFS can accurately enforce the Dirichlet and Neumann boundary conditions and efficiently restrain nonphysical liquid/mass penetrations near the solid surfaces. Applications of the present method to study more complex GLS problems at large density ratios $O\left({10}^3\right)$, including droplets impacting porous solid structures and a flapping wing, have also been carried out to further demonstrate its reliability and high potential.

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• Drop interactions
• Flow-structure interactions