Numerical simulation for liquid bridge reopening process with two-phase lattice boltzmann method

Based on the recently proposed and developed phase-field lattice Boltzmann method, a computational model is established to simulate the reopening process of blocked human pulmonary airway. The two-phase computational model is established following the free energy theory, and an order parameter is introduced for the description of two-phase interface, which evolves according to the Cahn-Hilliard equation. The model thus has a solid physical foundation. A pressure distribution function is utilized for the hydrodynamic equations, which facilitates minimizing the discretization error of the density gradient to weaken the numerical instability. In addition, an interfacial force of potential form is adopted, which produces much smaller spurious velocities at the interface by comparing with its counterpart of pressure form. The model is used to simulate the liquid bridge reopening process, and the effect of capillary number is analyzed. There exists a critical capillary number, beyond which the axial thickness of the liquid bridge decreases, and finally ruptures, leading to the reopening of blocked human pulmonary airway. Two kinds of reopening processes are reproduced, and they are classified by whether droplets are formed. The reopening process without droplet formed undergoes a more severe pressure jump. This approach is expected be used to further investigate physiology and pathology of human respiratory system and fundamental immiscible two-phase flow phenomenon in microchannels.