Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 244

the left cavity ( vortex B ) all point inwards. Vortex B shows the outer streamlines of
the vortex directed inwards while the inner streamlines are directed outwards from
the centre.
The nasal valve is considered as a region rather than an oblique cross-sectional
area of the nasal passageway and resembles a constriction-expansion region which
causes the majority of the total airflow resistance. The streamlines in the anterior nasal
valve are all directed from the outer wall towards the inner septum wall (Fig. 8.9 )
whereas in the right cavity, the opposite occurs (Fig. 8.10 )—the flow is directed from
the inner side, outwards. As the air enters the nasal valve region after the 90 ◦ turn,
the transition coupled with the narrowing geometry forces a majority of the flow
direction to come from the opposite side of the septum walls. This is consistent with
the larger contour areas (red-colour) of high velocity found for the right cavity. After
the flow is aligned and the airway begins to expand, the resistance at the walls causes
the flow to rebound and flow in the opposite direction. We will see in later case
studies that this flow feature is important for prediction of particle deposition. The
direction of the streamlines that initially accelerate from the outer wall will enhance
the deposition of inhaled particles onto the inner nasal septum wall side rather than
on the outer surfaces.

8.2.7 Flow Features in the Middle Turbinates

The same contour-streamline plot was applied to the middle turbinate area located
at 6.10 cm from the anterior nares. The streamlines show that flow is directed down-
wards with the bulk of flow concentrated in the upper and lower region close to
the septum walls. There are no visible vortices but some weak recirculation occurs,
possibly due to the narrow geometry (Fig. 8.11 ). Velocities in this region are lower

Right Left Right Left

a b

Fig. 8.11 Velocity field in the cross-section located at 6.10 cm from the anterior tip of the nose.
a Flow rate of 7.5 L/min. b At flow rate of 15 L/min