This work comprises an investigation of the fluid mechanics of nasal airflow, primarily
using computational fluid dynamics simulations, though with some flow visualisation
experiments. The objective of the work is to provide a basic understanding
of the flow phenomena that in turn govern transport and exchange processes in the
nasal airways. In keeping with the goal of elucidating the basic fluid mechanics,
simplified models of the nasal cavity airway were considered together with two representative
realistic models. Computations were performed using a commercially
available 3D laminar finite-volume solver (Fluent 6.3.26, ANSYS), for steady and
unsteady flow conditions.
The reduced models replicate the steady pressure loss vs. flow curve found in
realistic geometries, and in the unsteady case, confirm the validity of simple inertance
modelling to deduce the form of the pressure-flow loop. By selective inclusion/
exclusion of a simplified middle turbinate, the simulations reveal how the
turbinate redirects and controls inspired air. In the absence of the middle turbinate,
large scale instabilities were observed in the cavity flow and their strength and distribution
were seen to increase concomitant with increasing flow rate. It was further
identified that the inclusion of this turbinate reduced large scale flow instability and
that flow partitioning was predominantly determined by the impingement of the
inspiratory jet on its surface.
The consequence of the narrow mean passage width characteristic of the nasal
airways is explored by comparing an idealised 2D model with 3D geometries of
increasing calibre. A strong interrelationship was found to exist between geometric
and flow characteristics. In particular, the narrow width of the normal nasal airways
is shown to exert a strongly stabilising effect on the mean flow during inspiration. In
3D, whereas increasing calibre width is associated with a progressive destabilisation
of the flow, for the same inspiratory flow rate, there would be a concomitant drop
in maximum velocity. The computational results moreover detail the evolution of
the time-dependent flow within the simplified anatomies and the instability at the
margins of the inspiratory jet are shown to compare well with those found in flow
visualisation experiments.
In the last part of the thesis, steady modelling of the flow in the anatomically
realistic geometries is used to investigate their heat and water exchange capacity as
well as the characteristics of particle transport and deposition. These results are
related to those found in the idealised models.