All NSP patients had a preoperative CT scans, but only four had postoperative CT scans (2 posterior septectomy patients and 2 flap repair patients). These CT scans enabled the construction of CFD nasal airway models for each subject using methods described previously 9 (link), 16 (link), 17 , and only brief descriptions are provided here. The CT scans were imported into the commercial software AMIRA (Visualization Sciences Group, Hillsboro, OR, USA) to extract nasal cavity geometry. After necessary segmentation, smoothing, and correction for artifacts, a three-dimensional surface geometry of the nasal airway was generated. Then the commercial grid generator ICEM CFD (Ansys, Inc., Canonsburg, PA, USA) was applied to generate a computational mesh. A four-layer prism mesh was adopted at the boundary with a total height of ~0.2 mm near the mucosal surface to more accurately model the rapidly changing near-wall air velocity. A typical initial nasal cavity mesh with boundary layers contained between 1 million and 3 million finite elements. Then the initial meshes were refined by gradient adaptation and boundary adaptation until grid independence of the solutions was achieved. After the grid adaptation, the final nasal cavity mesh ranged from 1.5 million to 3.3 million hybrid finite elements.
Next, the solutions of the three-dimensional steady Navier-Stokes equations were obtained using the commercial software package FLUENT 16.2 (Ansys, Inc., Canonsburg, PA, USA), by applying a physiologically realistic pressure drop of 15 Pa between the nostrils and the nasal pharynx 18 . This pressure drop of 15 Pa was chosen to simulate restfully breathing, a state that is most relevant to patients’ symptoms during routine daily life 19 . Room air temperature of 20°C was set at the nostrils. Along the nasal mucosal walls, the usual no-slip velocity condition was applied, and the wall is assumed to be rigid and at constant temperature of 35°C. The numerical solutions of the continuity, momentum and energy equations were determined using the finite-volume method. A second-order upwind scheme was used for discretization. The SIMPLEC algorithm was used to link pressure and velocity. The discretized equations were then solved sequentially using a segregated solver. Convergence was obtained when the scaled residuals of continuity and momentum quantities were less than 10−5. The convergence residual of the energy equation was set as 10−8.
Next, the solutions of the three-dimensional steady Navier-Stokes equations were obtained using the commercial software package FLUENT 16.2 (Ansys, Inc., Canonsburg, PA, USA), by applying a physiologically realistic pressure drop of 15 Pa between the nostrils and the nasal pharynx 18 . This pressure drop of 15 Pa was chosen to simulate restfully breathing, a state that is most relevant to patients’ symptoms during routine daily life 19 . Room air temperature of 20°C was set at the nostrils. Along the nasal mucosal walls, the usual no-slip velocity condition was applied, and the wall is assumed to be rigid and at constant temperature of 35°C. The numerical solutions of the continuity, momentum and energy equations were determined using the finite-volume method. A second-order upwind scheme was used for discretization. The SIMPLEC algorithm was used to link pressure and velocity. The discretized equations were then solved sequentially using a segregated solver. Convergence was obtained when the scaled residuals of continuity and momentum quantities were less than 10−5. The convergence residual of the energy equation was set as 10−8.
