Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 243

vortex A

Vortex A

Right Left

a

vortex B

Vortex B

Right Left

b

Fig. 8.10 Velocity field in the coronal cross-section located at 3.20 cm from the anterior tip of the
nose. a At flow rate of 7.5 L/min and b At flow rate of 15 L/min

of the wall along with the bulk flow that exists in the upper regions restricts the
flow in the lower regions (light blue colour) and forces the flow to recirculate thus
formulating vortices. For the cross-section located at 2.6 cm from the anterior tip of
the nose, two vortices in the right cavity and one in the left are found for a flow rate
of 7.5 L/min (Fig. 8.9 a). When the flow rate increases to 15 L/min, the number of
vortices in both of the cavities increases in the low flow regions and the streamlines
are more dispersed (Fig. 8.9 b).
At the cross-section located at x 3 . 2 cm from the anterior tip of the nose, the

bulk flow is concentrated more centrally as the air stream is developing (Fig. 8.10 ).
At a flow rate of 7.5 L/min, there are two vortices in the left cavity while in the
right cavity some recirculation occurs, forming weaker vortices (Fig. 8.10 a). The
direction of the streamlines in vortex A all point to the centre of the vortex, which
demonstrates that the axial velocity gradient is positive and the pressure gradient
is negative along the axial direction (Escudier 1988; Stabl 1992). As the flow rate
increases to 15 L/min, the magnitude of the recirculation and hence the vortices
increase (Fig. 8.10 b). The direction of all the vortices except for the upper vortex in

=