Unsteady analysis of the airflow in human nasal airway – a computational study

Abstract

Background and objective

Nasal cavity is the first line of defence against toxicants and pollutants. A deep understanding of the realistic airflow in the complex geometry is crucial to evaluate pollution impact and initiation of various respiratory diseases. Human respiration by nature is unsteady, having two phases – inhalation and exhalation. While prior studies are predominantly on the steady state considering only the inhalation phase, we are curious to understand and investigate the unsteady nature of human respiration.

Methods

A sinusoidal unsteady profile simulating a complete breathing cycle at a flow rate of 10 L/min is considered in this study. We have reconstructed a realistic human nasal cavity model from CT scans and with Ansys Fluent we have analysed the flow field. The time-evolving flow patterns and wall shear stress, in particular during the distinctive accelerating and decelerating breathing phases, are extracted. Critical transient insight to the unsteady breathing which is largely unknown in a steady simulation is revealed. Finally, the breathing air flux in the olfactory region are calculated under the transient breathing condition.

Results

Evolving flow pattern at different time instants gives a significant variation of the flow dynamics which would not be understood in a steady study. The main differences in inhalation and exhalation are the regions where the main flow is dominant, the location of the vortices around the olfactory and wall shear stress patterns. In addition, past history of peak flow has noticeable effects on flow fields during the deceleration phase, especially when the breathing rate is low. Finally, flow pathways into the olfactory region varies during inhalation and exhalation phases.

Conclusion

The cyclic information provides critical transient insight to the unsteady breathing which is largely unknown in a steady study. In the context of a fast-growing interest in nasal transport to accurately evaluate pollution impact and pathogen deposition, investigation on the flow and particle depositions under unsteady condition is valuable and highly desired.