AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Recommendations for Reducing CFD Model Variability and Matching Experimental Data When Simulating Microparticle Deposition with Two-Equation Turbulence Models
KARL BASS, Worth Longest, Virginia Commonwealth University
Abstract Number: 137 Working Group: Health Related Aerosols
Abstract When modeling flow through the respiratory tract, two-equation turbulence models provide several advantages over more complex models, which include computational efficiency, mature model development, and successful in vitro and in vivo validations in previous studies. However, CFD models often require several iterations of parameter selection before capturing experimental aerosol deposition data. This study aims to determine both mesh and CFD solution parameters that enable the accurate simulation of microparticle deposition under flow conditions consistent with the upper respiratory airways, including turbulent flow, evaluated in a model 90-degree bend system. First, parameters that control the near-wall cell layers are manipulated to produce four distinctly different meshes, which vary from settings that are ideal for the nasal cavity to the recommended industry standard. A range of CFD models and their parameters are then applied to these meshes, including spatial discretization schemes, wall roughness, and anisotropic turbulence correction. Both hexa- and tetrahedral meshes are evaluated, with tetrahedral meshes being more suitable for intricate and detailed airway geometries. The results are compared to evaluate which CFD model parameters produce the least amount variability between the meshes, with the intention of reducing the variability in the meshes of complex geometries. Focus is applied to analyzing the near-wall turbulence kinetic energy, as this drives deposition by turbulent dispersion. Finally, numerical results are compared with experimental data available from the literature for a range of microparticle sizes from 1 to 7µm. The recommendations provide a good match between numerical and experimental microparticle deposition results for Stokes and Reynolds numbers that are similar to the transport of pharmaceutical aerosols through the upper airways. Applying these recommendations to future CFD models of the respiratory tract will reduce the effort that is required to capture respiratory aerosol deposition.