Numerical simulation of the high–frequency oscillatory ventilation in generic models of the human airways

Kurzfassung

To improve the understanding of the gas transport mechanisms under conditions of high-frequency oscillatory ventilation (HFOV) we perform numerical simulations of the unsteady flow in simplified models of the human airways using time varying Dirichlet boundary conditions (BC) for the pressure. The flow fields in a generic trachea show excellent agreement with the analytical solution with an average absolute deviation of less than 10^2 for non-dimensional frequencies up to Wo=14. Nonetheless, the computational effort increases for high Wo simulations due to a long relaxation phase and strong velocity gradients near the wall despite of relatively low Reynolds numbers. We also simulated the flow within an endo-tracheal tube comprising turbulent as well as laminar flow behaviour throughout the oscillation cycle. Finally, we used the Dirichlet pressure BCs on multiple open outlets at symmetric bifurcation and three-generation airway models, while guaranteeing mass conservation. Employing identical and slightly different pressure values at the distal bifurcation ends, flow fields are reproduced, similar to that occurring under conditions of uneven physiological behaviour of different lung regions (e.g. pendelluft).