Effect of inlet swirl on dry powder distribution through the oropharyngeal route of human respiratory tract

This study utilized computational fluid dynamics (CFD) to investigate the impact of swirling airflow on dry powder drug particle transport and deposition in a realistic human respiratory tract model extending from the oral cavity to the sixth bronchial bifurcation. The model incorporated steady-state inspiratory flow conditions and discrete phase modeling to simulate the behavior of 1 μm–25 μm particles at various flow rates (5–45 L/min), swirl numbers (SN = 0, 0.25, 0.4, 0.85), and swirl directions (clockwise [CW] and anticlockwise [ACW]).

The results demonstrated that moderate swirling flow improves drug targeting in the distal lung. Specifically, a CW swirl at Sn = 0.4 with a low flow rate of 10 L/min achieved the most efficient deposition, delivering approximately 75 % of 5 μm particles to the distal region, while minimizing unwanted deposition in the oropharyngeal region. At a standard condition of 30 L/min and 1 μm particles, a CW swirl at SN = 0.4 yielded the highest in the distal region deposition (51.37 %) compared to only 23.97 % in the no-swirl case.

Flow visualization confirmed that the swirl promotes favorable jet redirection and enhanced particle residence time, while maintaining wall shear stress within physiologically safe limits. Excessive swirl (SN = 0.85) increased deposition in the oropharyngeal region, due to inertial impaction. These findings highlight the potential of controlled swirl, especially CW swirl at low flow rates, as a practical strategy to improve DPI design for targeted pulmonary drug delivery.