Simulation of fluid dynamics and particle transport in realistic human airways
Creators: name: Choi, Lok
Publisher: name: RMIT University
Year: 2024

description: The aim of this research is to numerically study the flow characteristics and particle transport within human airways, specifically, the upper airways starting from the trachea to major bronchi. Different entering flow rates and frequencies are the major parameters varied in order to analyze the effect on particle deposition. There have been numerous flow-particle studies in human airways at the current level of knowledge, but one major contribution from this research is that realistic geometries of human airways are used to study flow-particle interaction, in which the airway models are reconstructed from computerized tomography (CT) data of real human tracheobronchial airways.<br><br>CFD techniques for this particular study are developed based on the literature review of other similar studies. The k-omega turbulence model was found to be suitable for this type of study. Evaluation and validation of the numerical approach and results were carried out by comparing with other experimental studies in terms of geometrical details, lobar flow distribution in percentage of the tracheal flow, velocity profile, and deposition efficiency. This approach was found to be appropriate. Based on the developed techniques, two aerosol delivery methods used clinically were studied. Similarly, results were compared with experimental and theoretical results for validation. It was found that slower breathing gives better transportation into the lung periphery and faster breathing gives higher deposition rate in the first few generations of the tracheobronchial airways. Visualization techniques were also developed where deposition pattern provided easy-to-understand illustration to personnel with no engineerin g background. It showed that particles often concentrate along the carinal ridges at the bifurcations and inner walls leading down from carinal ridges. The study of the interaction between flow and particle described how skewed velocity profile and vortices in secondary velocity profile affected regional deposition efficiency as well as deposition pattern. The study also confirmed that right main bronchi usually capture more particles than left side as other researchers observed.<br><br>Several important findings are summarized based on this research: • Stokes number although is a good indicator in providing regional deposition efficiency information, the local 'hot-spots' still heavily rely on visualization of deposition pattern. • Generally speaking, high flow rate and/or large particle size lead to high deposition efficiency in the first bifurcation and cartilaginous rings along the trachea. • Bronchi in the right hand side usually capture more particles than bronchi in the left hand side. • Particles often concentrate along the carinal ridges at the bifurcations and inner walls leading down from carinal ridges. • In the aerosol delivery study, short inhalation and exhalation with small air volume gives lower deposition in the first six generations than long inhalation with large air volume. Therefore, if deposition into deeper locations of the lung is preferred, then slower breathing is required. On the contrary, if the treatment location is in the first few generations, then faster or moderate breathing is more ideal. • Deposition efficiency and deposition pattern can be estimated roughly from the velocity profile along the airway.<br>