Evaluation of tracheal stenosis: Comparison between CFD and PIV evaluation in the smooth and cartilaginous trachea model

Given the inaccessibility of the respiratory system, computational fluid dynamics (CFD) has become an essential tool used to understand the flow characteristics in the complex flow inside the human airways. However, validation of the simulations with experimental work is crucial to have accurate results, especially with CFD models that struggle to predict flow separation. In this study we evaluate a simplified trachea model with stenosis. This condition is characterized by concentric thickening of the soft tissue within the tracheal lumen. Two models are used to evaluate the flow characteristics in an index-matched facility: a model with smooth wall and a model with wall corrugations simulating cartilaginous rings with PDMS were constructed. The flow rate is set comparable to the resting breathing state Reynolds number, Re_D=3400. We use particle image velocimetry (PIV) and refractive index matching to measure the flow field. Additionally, we numerically simulate the flow in the same geometry using different CFD models and compare this results to the experimental measurements. This study will help understand the strengths and limitations of CFD models for respiratory fluid dynamics research and provide a baseline for future CFD studies particularly the smooth surface assumption