Simulated airflow and rigid fiber behavior in a realistic nasal airway model

Abstract

Particles may become airborne due to numerous natural and anthropogenic processes. The nose provides protection for the respiratory system through deposition that prevents particles from reaching more sensitive regions. A series of simulations have been conducted to better predict the deposition efficiency within the nasal passages. Computational fluid dynamics coupled with Lagrangian particle tracking have been used to estimate the deposition of both fibrous and spherical particles. MRI data was collected from the left and right passages of an adult male of mass 120.2 kg and height 181.6 cm. The two passages were constructed into separate computational volumes consisting of approximately 950,000 unstructured polyhedral cells each. A steady, incompressible, laminar flow model was used to simulate the inhalation portion of a human breathing cycle. Volumetric flow rates were varied to represent the full range of human nasal breathing. Qualitatively, the simulated airflow field was shown to agree well with previously published in vitro studies on different nasal replicas. An empirical expression for pressure drop as a function of flow rate that takes the form of Rohrer’s equation is proposed based on the measured data. Deposition efficiency was shown to depend on fiber aspect ratio, particle size, and flow rate. Nasal geometry was also identified as a key factor affecting deposition. A modified Stokes number is proposed along with a novel empirical expression for fiber deposition efficiency in the nasal airway.