The laminar flow in the small bronchial tubes is quite complex due to the presence of vortex-dominated, secondary flows. Contributing to this complexity are the geometrical characteristics of the bronchial tubes that include asymmetric and nonplanar branching. These secondary flow fields play a crucial role in particle deposition; however, the actual mechanisms that determine the particle distributions are not fully understood. The research reported here increases understanding of this phenomenon by studying flow structure/ particle interaction in the small bronchial tubes for steady and unsteady respiratory conditions. Specifically, the effects of simultaneous nonplanar and asymmetric branching were investigated. The nonplanar model was generated by applying a 90◦ out-of-plane rotation to the third-generation branches. Steady-state inspiratory flows for a Reynolds number of 1,000 and unsteady periodic flows with a 30-respiration-per-minute breathing frequency were simulated in three-generation, asymmetric, planar and nonplanar models. The asymmetry and nonplanarity produced asymmetric secondary flow patterns and unequal mass flow partitioning in the third-generation branches. Ten micron water droplet deposition in the nonplanar model was found to be significantly different from the planar model, demonstrating the impact of simultaneous nonplanar and asymmetric branching. The unsteady nature of the flow also affected particle deposition. Particles released at the same instantaneous inflow conditions during off-peak inhalation conditions, generated significantly different particle deposition patterns. The differences were attributed to the high temporal variations of the fluid velocities at these off-peak times and history effects in the flows. It was also observed that the initial particle velocities had a significant impact on particle deposition. The study of flow structure and particle interaction was facilitated by the development of a novel visualization technique that employs finite-time Lyapunov exponents (FTLE). This research provides a better understanding of the fluid dynamics driving the particle deposition in the bronchial tubes.

Mechanical ventilation can be a life saving treatment. However, due to the inhomogeneous and anisotropic behavior of the lung tissue, ventilation can also lead to overdistensions of lung regions whereas other areas remain even collapsed. A first step is a more comprehensive understanding of the flow mechanics under normal breathing conditions in a healthy lung as well as for a diseased, collapsed lung. This is the aim of this work. Therefore, a realistic model of the upper human airways has been generated at which experimental and numerical investigations could be carried out. Experimentally, the flow was analyzed by means of Particle Image Velocimetry (PIV) measurements which revealed new details about the flow patterns occurring during different ventilation frequencies. Numerical results were in good agreement with the experimental results and could provide new details about the three-dimensional flow structure and emerging secondary flow within the upper airways. The study of reopening of collapsed airways has shown that larger frequencies lead to airway reopening without overdistension of already open parts. Higher frequencies also lead to homogenization of mass flow distribution within the human lung. / Künstliche Beatmung ist meist eine lebensrettende Maßnahme. Aufgrund der räumlich anisotropen und inhomogenen Eigenschaften der Lunge kann die Beatmung jedoch auch zu einer Schädigung der Lunge führen. Daraus ergibt sich die Forderung einer „Protektiven Beatmung“. Ein erster Schritt dahingehend ist ein verbessertes Verständnis der Atmung und Beatmung am Beispiel der gesunden sowie kranken, teilweise kollabierten Lunge. Dies ist das Ziel der Arbeit. Hierfür wurde ein realistisches Modell der oberen Atemwege (Tracheobronchialbaum) angefertigt. An diesem Modell können sowohl experimentelle als auch numerische Untersuchungen durchgeführt werden. Experimentell wurde die Strömung mittels Particle Image Velocimetry (PIV) untersucht, wobei neue Details bezüglich der auftretenden Strömungsmuster für unterschiedliche Frequenzen gefunden wurden. Numerische Strömungsberechnungen stimmen gut mit den experimentellen Ergebnissen überein. Dreidimensionale Strömungsstrukturen sowie die Entwicklung von Sekundärwirbeln in der Lunge konnten erklärt werden. Eine Studie am kranken, teilweise kollabierten Lungenmodell zeigte, dass mit steigender Frequenz kollabierte Bereiche wiedereröffnet werden können. Höhere Frequenzen führen weiterhin zu einer Homogenisierung der Massenstromverteilung in der Lunge.