Analysis of basic flow regimes in a human airway model by stereo-scanning PIV

Abstract

The detailed understanding of the human lung flow is of high relevance for the optimization of mechanical ventilation. Therefore, the spatial and temporal development of the flow field in a realistic human lung model is investigated for several oscillatory flow regimes using stereo-scanning particle-image velocimetry (PIV). The flow in the right primary bronchus is always measured for a complete sinusoidal ventilation cycle. Three Reynolds and Womersley number sets describing viscous (Re = 10; α = 1.5), unsteady (Re = 40; α = 5), and convective (Re = 150; α = 1.5) regimes are defined to cover various dominating fluid mechanical effects. In addition, multi-plane PIV measurements are performed to analyze steady laminar (Re = 150) and turbulent (Re = 2,650) flow at inspiration and expiration. The steady results show that the maximum velocity is shifted to the outer wall at inspiration and toward the inner wall of the bronchial bend at expiration. At inhalation, a U-shaped high-speed velocity profile develops only inside the left primary bronchus, whereas both primary bronchi contain one vortex pair. During expiration, the vortex pairs from each main bronchus merge into a two-vortex-pair system inside the trachea. From the oscillatory findings, it is evident that an undersupply for the right upper lobe is noticed at low ventilatory frequencies, whereas high-frequency flow leads to a more homogeneous ventilation. The analysis of the temporal development of the absolute velocity in the center plane shows a variable phase lag. Unlike the flow in the unsteady regime, the flow of the viscous flow domain (α = 1.5) is in phase with the applied pressure gradient. Additionally, a premature outflow of the upper right lung lobe can be observed in the unsteady flow regime.