Numerical simulation of airflow in the human nasal cavity.

An anatomically correct finite element mesh of the right human nasal cavity was constructed from CAT scans of a healthy adult nose. The steady-state Navier-Stokes and continuity equations were solved numerically to determine the laminar airflow patterns in the nasal cavity at quiet breathing flow rates. In the main nasal passages, the highest inspiratory air speed occurred along the nasal floor (below the inferior turbinate), and a second lower peak occurred in the middle of the airway (between the inferior and middle turbinates and the septum). Nearly 30 percent of the inspired volumetric flow passed below the inferior turbinate and about 10 percent passed through the olfactory airway. Secondary flows were induced by curvature and rapid changes in cross-sectional area of the airways, but the secondary velocities were small in comparison with the axial velocity through most of the main nasal passages. The flow patterns changed very little as total half-nasal flow rate varied between resting breathing rates of 125 m/s and 200 ml/s. During expiration, the peaks in velocity were smaller than inspiration, and the flow was more uniform in the turbinate region. Inspiratory streamline patterns in the model were determined by introducing neutrally buoyant point particles at various locations on the external naris plane, and tracking their path based on the computed flow field. Only the stream from the ventral tip of the naris reached the olfactory airway. The numerically computed velocity field was compared with the experimentally measured velocity field in a large scale (20x) physical model, which was built by scaling up from the same CAT scans. The numerical results showed good agreement with the experimental measurements at different locations in the airways, and confirmed that at resting breathing flow rates, airflow through the nasal cavity is laminar.