Investigation of pulsatile flow in the upper human airways

The pulsatile flow field in the human lung is numerically and experimentally investigated. The realistic lung geometry of a human subject was acquired down to the sixth generation of bifurcation and used as a tra cheobronchial model. The numerical analysis is based on a lattice–boltzmann method which is particularly suited for flows in extremely intricate geometries such as the upper human airways. The measurements are performed via the particle-image velocimetry method in a transparent cast generated from the original data set. Experimental and numerical results are analyzed in a comparative way and a thorough discussion of the three-dimensional flow structures emphasizes the unsteady character of the flow field. It is evidenced that the asymmetric geometry of the human lung plays a significant role for the development of the flow field in the respiratory system. Secondary vortex structures and their temporal formation are analyzed and described in detail for two respiration frequencies. It is shown that the qualitative structure of the intricate flow field does not vary if a critical mass flux rate is exceeded. at inspiration, the primary flow shows separated flow regions and is highly influenced by secondary flow structures. by contrast, at expiration the primary flow distribution is far more homogeneous with a higher level of vorticity.

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