title: Influence of Mesh Density on Airflow and Particle Deposition in Sinonasal Airway Modeling.
abstract: BACKGROUND
  There are methodological ambiguities in the literature on mesh refinement analysis for computational fluid dynamics (CFD) modeling of physiologically realistic airflow dynamics and particle transport in the human sinonasal cavity. To investigate grid independence in discretization of the (sino)nasal geometry, researchers have considered CFD variables such as pressure drop, velocity profile, wall shear, airflow, and particle deposition fractions. Standardization in nasal geometry is also lacking: unilateral or bilateral nasal cavities with and without paranasal sinuses have been used. These methodological variants have led to inconsistencies in establishing grid-independent mesh densities. The aim of this study is to provide important insight in the role of mesh refinement analysis on airflow and particle deposition in sinonasal airway modeling.
  
  
  METHODS
  A three-dimensional reconstruction of the complete sinonasal cavity was created from computed tomography images of a subject who had functional endoscopic sinus surgery. To investigate airflow grid independence, nine different tetrahedral mesh densities were generated. For particle transport mesh refinement analysis, hybrid tetrahedral-prism elements with near-wall prisms ranging from 1 to 6 layers were implemented. Steady-state, laminar inspiratory airflow simulations under physiologic pressure-driven conditions and nebulized particle transport simulations were performed with particle sizes ranging from 1-20 μm.
  
  
  RESULTS
  Mesh independence for sinonasal airflow was achieved with approximately 4 million unstructured tetrahedral elements. The hybrid mesh containing 4 million tetrahedral cells with three prism layers demonstrated asymptotic behavior for sinonasal particle deposition. Inclusion of boundary prism layers reduced deposition fractions relative to tetrahedral-only meshes.
  
  
  CONCLUSIONS
  To ensure numerically accurate simulation results, mesh refinement analyses should be performed for both airflow and particle transport simulations. Tetrahedral-only meshes overpredict particle deposition and are less accurate than hybrid tetrahedral-prism meshes.
authors.affiliation: 1 Division of Otolaryngology, Head and Neck Surgery, Duke University Medical Center , Durham, North Carolina.
authors.forename: Dennis O
authors.initials: DO
authors.lastname: Frank-Ito
authors.affiliation: 2 Department of Otolaryngology, Head and Neck Surgery, University of North Carolina , Chapel Hill, North Carolina.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wofford
authors.affiliation: 3 Applied Research Associates, Inc. , Raleigh, North Carolina.
authors.forename: Jeffry D
authors.initials: JD
authors.lastname: Schroeter
authors.affiliation: 2 Department of Otolaryngology, Head and Neck Surgery, University of North Carolina , Chapel Hill, North Carolina.
authors.forename: Julia S
authors.initials: JS
authors.lastname: Kimbell
keywords: airflow; computational fluid dynamics; hybrid mesh; mesh refinement; particle deposition; prism elements; sinonasal cavity; tetrahedral meshes