  Localized vortices can have significant influence on transport of inhaled
particles through the upper respiratory tract. These vortices have complex
three-dimensional structure with details dependent on the anatomical geometry.
Using a highly simplified model, we demonstrate that changes in transport
characteristics with geometric distortion can be estimated by accounting merely
for the net strength and location of the vorticity in a two-dimensional
projection. Test cases consider 30 L/min inhaled airflow containing suspended
spherical water droplets from 1 micrometer to 30 micrometers in diameter
through (1) a healthy upper respiratory tract and (2) a distorted variation
mimicking a glottic tumor. The reduced-order model approximates the system by a
two-dimensional potential flow with embedded point vortices having features
derived from Large Eddy Simulations of inhaled airflow through anatomically
realistic, tomography-based, three-dimensional tracts. The effects of vorticity
and particle size on changes in particle transport are shown to be consistent
between the reduced-order model and the full-scale simulations.
