The effect of intrasubject variation on the turbulent flow and aerosol deposition in the extrathoracic airways is studied in two realistic mouth-throat geometries from the same subject. An immersed boundary method is applied which simplifies the task of grid generation for the complex extrathoracic geometries and allows the use of a structured grid solver. Curvilinear grids that roughly follow the shape of the geometries are adopted, allowing for much higher resolution within the geometries than Cartesian grids commonly used in IB methods. An added advantage is that the grid lines are approximately aligned with the streamlines, which reduces numerical diffusive errors. The numerical simulations allow us to explain in vitro aerosol deposition data in the literature for the same mouth-throat models. The position of the tongue during inhalation is shown to have a significant impact on both the mean flow patterns and the turbulence intensities, which in turn affects extrathoracic deposition
