Liquid plug transport and splitting in bifurcated airways by lattice Boltzmann method

In pulmonary treatment, specific exogenous fluids are injected into the airways, forming a liquid plug that propagates through the trachea and the bronchial structures. The transport and splitting processes of these liquids in airway branching are crucial for optimizing the distribution of the therapeutic liquid in the lungs. This study simulates these processes using the chemical–potential lattice Boltzmann method based on a physiologically realistic bifurcated airway model. The results show that as the body force decreases, the effect of gravity becomes more dominant, resulting in a greater volume of liquid entering the lower daughter branch. This gravitational effect leads to an apparent asymmetry in the splitting behavior of the liquid plug, accompanied by asymmetric shear stress fluctuations on the upper and lower bifurcation walls. Notably, positive peaks in shear stress are observed at the front interfaces of the split liquid plugs. As the roll angle decreases, the splitting ratio of the liquid plug increases, while the pitch angle has a minimal effect on the splitting ratio unless the capillary number is small. Additionally, the shorter the initial length of the liquid plug, the shorter the time required for splitting, and the smaller the splitting ratio. The thickness of the liquid film has little effect on the splitting time, but the drag force between the liquid film and the liquid plug affects the quality of the liquid entering the daughter airway. These findings provide valuable insight into the dynamics of liquid plug transport and splitting, which can inform the optimization of pulmonary treatments involving therapeutic liquid delivery.