Unified Simplified Multiphase Lattice Boltzmann Method For Ferrofluid Flows And Its Application

A unified simplified multiphase lattice Boltzmann method (USMLBM) is constructed in this work for simulating complex multiphase ferrofluid flows with large density and viscosity ratios. In USMLBM, the Navier-Stokes equations, the Poisson equation of the magnetic potential, and the phase-field equation are utilized as the ferrohydrodynamics behavior modeling and interface tracking algorithm. Solutions of the macroscopic governing equations are reconstructed with the lattice Boltzmann framework and resolved in a predictor-corrector scheme. Various benchmark tests demonstrate the efficiency and accuracy of USMLBM in simulating multiphase ferrofluid flows. We further adopt USMLBM to analyze in detail the mechanisms of bubble merging inside a ferrofluid under a uniform external magnetic field. The numerical results indicate that the bubbles tend to move toward each other and further merge together, even for a large initial separation between the bubbles. Due to complex interaction between the bubbles and the ferrofluid during the magnetophoretic acceleration process, the nonlinear effect on bubble merging is observed when the initial separation increases. Moreover, at a larger initial separation, the shape of bubbles seems to be not sensitive to the initial separation.