Effects of nostril orientation on airflow dynamics, heat exchange, and particle depositions in human noses

•Nostril orientation has a significant effect on ventilation and cellular-level depositions.•Nostril orientation has a negligible effect on main flow turbulences and total depositions.•The near-wall vertex structures exhibits significant dependence on the nostril angle, which significantly affects the near-wall stress and heat transfer rate.•Retaining actual nostril angle is essential for reliable prediction of nose functions.

The orientation of the nostrils is thought to regulate airflow dynamics and associated functions of the nose. Previous studies have used different nostril orientations ranging from downward-directed (90°) to anterior-directed (0°). However, the influences of nostril orientation on nose functions have not yet been studied. The objective of this study is to systematically assess the influences of the orientation of the nostrils on airflow, heat exchange, and particle behaviors during inhalation by means of image-based modeling. Nose models with five different nostril angles were developed by modifying the vestibule of an anatomically accurate nose airway geometry reconstructed from magnetic resonance imaging. Large eddy simulations and a Lagrangian tracking model were used to simulate airflow dynamics and particle transport with a wide range of inhalation conditions (4–45 L/min) and particle sizes (1–20μm). Results showed that nostril orientation exerted a significant impact on superior/inferior meatus ventilating and sub-regional and local depositions. The downward-directed nose model has the highest flow flux to the superior meatus and lowest flux to the nasal floor. The turbulence intensity inside the main flow is negligible; however, there are substantial vortex formations in the near-wall region. The anterior-directed nose model has the strongest near-wall vortices in the valve vicinity, which is coincident with the location of the highest wall shear stress and heat exchange, and has a close correlation with local particle deposition patterns. Results of this study indicate that the actual nostril angle should be preserved to reliably predict respiratory functions of a pathological/postsurgical nose, or the delivered doses of a topical intranasal delivery.