Numerical simulation for pulmonary airway reopening in alveolar duct by lattice Boltzmann method

Aerosols, which are generated by the rupture of the liquid plug in the pulmonary respiratory tract, are important carriers of the viruses of infectious respiratory diseases, such as flu, tuberculosis, COVID-19, and Measles. In this study, we investigate liquid plug rupture and aerosol generation in the low respiratory tract with the alveolar structures by the chemical-potential multiphase lattice Boltzmann method. In a single alveolus duct, the opening expedites a unilateral break of the liquid plug due to a portion of the liquid flowing into the alveolus, and a microdroplet is yielded in the rupture. Aerosol would be deflected and reintegrated into the liquid film when the force is not great enough, which generates greater shear stresses to the inner wall where the microdroplet falls. In two alveoli duct, the rupture times of the upper and lower neck of the liquid plug depend on the radius ratio of the upper and lower alveolar. After the rupture of the liquid plug, the movement trajectory of the droplet is influenced by the alveoli structure to move forward or upward deflection. Interestingly, with the increase of radius ratio of the upper and lower alveolar, the mass of the fluid inflow into the alveoli decreases, while the mass of the aerosol generated by the rupture increase. This work contributes to understanding complex flow properties in the pulmonary airways, and the model can be extended to study the transport of liquid plugs and the generation of aerosol particles in more complex respiratory tract structures.