Mesh Refinement Study of Flow and Particle Deposition in Human Lung Airway Model

Abstract

Simulation of flow and particle deposition in multigenerational bronchial tube geometries is a nontrivial problem. The lung airway geometry is quite complex due to asymmetry, nonplanarity and multiple generations. There are 23 airway generations in the human lung. The complexity of the airflow increases with an increasing number of generations. Particle deposition in bronchial tubes is strongly affected by these complex flow fields and bronchial tube geometry. Determination of mesh independence requirements of CFD solutions in large-scale, multigenerational models can guide the optimum use of computational resources. In this paper, we investigate the mesh independence of the solution in an idealized lung geometry consisting of a nine-generation, nonplanar, bronchial tube model using our hybrid (finite element/finite volume), matrix free, parallel CaMEL flow solver. Four mesh resolutions were considered for the mesh refinement study. Steady-state inspiratory flow was simulated with an inlet Reynolds number of 319. The dimensionless pressure drop, primary velocity profiles, and mass flow distribution were investigated to assure mesh independence of the primary flow fields. The results showed minimal differences in these metrics for all four mesh resolutions indicating that a mesh independent primary flow was achieved for all four meshes. The mesh convergence of secondary flows was also investigated. The two finest meshes showed mesh convergence in terms of secondary flows. In addition, the particle transport for all the meshes were simulated using our Lagrangian based particle tracking model. The particle deposition was investigated by employing particle deposition efficiencies in each generation, RMS of FTLE difference values and FTLE difference maps. The results showed that as the meshes were refined; particle deposition efficiency differences and FTLE differences became smaller, suggesting that the solution was approaching mesh independence. The results indicated that, even though the primary flow fields showed mesh convergence for all the mesh refinements, the mesh convergence was achieved in terms of secondary flows and particle deposition for only the 2 nd and 3 rd refinement levels. This demonstrates the impact of secondary flows on the particle deposition as well as the importance of explicit investigation of the particle deposition employing meaningful metrics when performing a mesh refinement study in bronchial tube models.