A critical analysis of the CFD-DEM simulation of pharmaceutical aerosols deposition in upper intra-thoracic airways: Considerations on air flow

A well-corroborated numerical methodology ensuring reproducibility in the modeling of pharmaceutical aerosols deposition in the respiratory system via CFD-DEM simulations within the RANS framework is currently missing. Often, inadequately clarified assumptions and approximations and the lack of evidences on their quantitative impact on the simulated deposition phenomenology, make a direct comparison among the different theoretical studies and the limited number of experiments a very challenging task. Here, with the ultimate goal of providing a critical analysis of some crucial computational aspects of aerosols deposition, we address the issues of velocity fluctuations propagation in the upper intra-thoracic airways and of the persistence of secondary flows using the SimInhale reference benchmark. We complement the investigation by describing how methodologies used to drive the flow through a truncated lung model may affect numerical results and how small discrepancies are observed in velocity profiles when comparing simulations based on different meshing strategies. [Display omitted] •The way the airflow is driven in the simulations can cause significant differences in flow splitting and ventilation anisotropy.•To ensure adherence of simulations to experiments the air flow splitting must be measured and imposed in the simulations.•Secondary flow structures (vortices) persist up to the 7th generation growing in intensity rather than attenuating.•Secondary flow structures are extremely sensitive to the kind of mesh employed and to the refinement strategy adopted.•Air turbulence survives up to the 7th generation of the human airways.•Spatial/temporal correlations of air velocity fluctuations deserve more attention and further investigation.