The flow and the transport of particles in the human respiratory system dictate the effectiveness
of therapeutic aerosols used in inhaled drug delivery. The aerosol particles are
generally inhaled through the mouth, passing by the throat before reaching the targeted
areas in the lungs. Therefore, knowledge of the particle deposition in the mouth-throat
region is critical in the design of effective inhalation devices for optimum delivery to the
lungs. Numerical simulations offer a non-invasive and cost-effective alternative to in vivo
and in vitro tests. However, accurate prediction remains a challenge for numerical models
due to the complexity of the flow in the extrathoracic airways.
A robust immersed boundary method for flow in complex geometries is proposed. This
greatly simplifies the task of grid generation and eliminates the problems associated with
grid quality that exist for boundary-fitted grid techniques. The proposed method is an
extension to the momentum forcing approach onto curvilinear coordinates and applies an
iterative procedure to compute the forcing term implicitly, which stabilizes the scheme for
higher Reynolds numbers. The use of a curvilinear grid minimizes the number of unused
cells outside the geometry and increases the efficiency of the numerical scheme. The method
is validated against numerical and experimental data in the literature for a number of test
cases on both Cartesian and curvilinear grids. The results show good agreement with
previous studies.
Direct numerical simulations were performed in a number of realistic mouth and throat
geometries obtained from MRI scans. A Lagrangian particle tracking scheme was employed
to advance the particles dynamically, and total and regional deposition efficiencies were
determined and compared to in vitro data. The effect of inflow turbulence and intersubject
variation on deposition was studied. Geometric variation has a large impact on total
deposition whereas the effect of inflow turbulence is confined to oral deposition
