Numerical Simulation Of Fluid Dynamics Of Pulmonary Airway And Alveolar Tube

The COVID-19 epidemic is spreading globally,with a significant impact on the production and livelihood of all human beings.The rapid spread of SARS-Co V-2 is since the virus can be transmitted utilizing aerosols and infected through the respiratory tract.The hydrodynamic processes of the 13th bronchioles and 15th alveolar ducts of the human respiratory tract are essential sources of aerosol droplets,but their complex structure and microscale flow characteristics pose significant difficulties for in vitro experimental and theoretical studies.With the rapid development of modern computer technology,high-performance numerical simulation computational methods in complex micro-scale flows have become quite mature.Therefore,the mechanism of two-phase microflow in the pulmonary respiratory can be deeply explored using the computational simulation method.This paper presents a numerical simulation model of the pulmonary airway reopening based on the multiple-relaxation-time lattice Boltzmann method.Combined with Open MP parallel technology to improve the computational efficiency of the model simulation,it is used to study complex fluid dynamics phenomena in the pulmonary airways,focusing on investigating the mechanisms of aerosol droplets formation in the trachea.The multiple-relaxation-time lattice Boltzmann model investigated the two-phase flow mechanism in the 13th generation pulmonary airway.Based on validating the model,we analyzed the influence of the capillary number on the movement process of the liquid plug.We found that there is a critical capillary number of 0.267.When the capillary number is greater than the critical value,the thickness of the liquid plug gradually decreases,and reopening of the pulmonary airway is achieved.The simulations reproduced two types of pulmonary airway reopening with and without aerosol droplets generation.It was found that when aerosol droplets were generated,although the volume force increased by 50%,the damage to the tracheal wall was similar to that in the absence of aerosol droplets.The difference between the maximum and minimum wall pressure(P_max-P_min)and the shear force(?_max-?_min)was reduced by 4%and 9%,respectively.The influence of the thickness of the anterior liquid film and the tail liquid film was investigated by simulation.It was found that when the thickness of the anterior liquid film was thicker than that of the tail liquid film,larger aerosol droplets were formed in the pulmonary airways.Further studies found that aerosol droplet size,P_max-P_min,and?_max-?_min increased with increasing the pressure drop and liquid plug thickness;the opposite trend occurred with increasing the liquid film thickness.Then,a numerical computational model of the 15th generation alveolar duct was constructed,and simulation work on the alveolar duct was carried out.Comparing single and double alveolar ducts reopening to generate aerosol droplets,we found that the fluid plug ruptured rapidly after passing through the alveoli,with residual fluid flowing into the alveolar wall.Analysis revealed that the mass of the intra-alveolar fluid changed by approximately 20?g when the liquid plug thickness was increased from 0.5 R₁ to 1 R₁ at the pressure drop of 4?dyn.The effect of the alveolar tube reopening process on the wall was further investigated.Comparative results showed that the wall pressure was reduced by approximately 40%compared to the absence of aerosol particle formation,despite a 66.7%increase in the pressure drop.More significant damage to the trachea exists during alveolar duct reopening without aerosol droplets formation.The lattice Boltzmann model constructed in this paper can be further extended to study the formation mechanism of bioaerosols carrying infectious agents such as SARS-Co V-2 or influenza virus in the pulmonary respiratory tract,providing academic help in exploring the transmission and prevention of bioaerosols such as COVID-19.