Investigation of boundary condition effects on flow rate distribution in a human upper respiratory tract

Investigation of airflow behavior and distribution in the human respiratory tract has recently drawn the attention of researchers to study the particle movement and deposition in aerosol therapy and inhalation toxicology applications. Therefore, in this paper the steady-state flow behavior during inhalation in a human lung model has been numerically investigated. A three dimensional asymmetric and non-planar bifurcation model of trachea-bronchial airway was used in the present study. Computations were performed for two different boundary conditions: (a) the same flow rate for all the outlets and (b) the same static gauge pressure equal to zero for all the outlets. Reynolds numbers were chosen in the range of 1000 to 4000, corresponding to the breathing rates of 12-48 l/min. Detected reverse flow zones and the flow rate distribution were presented. Estimation of the flow rate distribution in the right (upper, middle and lower) lobes when using the second boundary condition was more accurate compared to the true distribution in the lungs. With increasing the inlet flow rate, flow rate distribution changed in cases where the second boundary condition was used but it was negligible. Reverse flow zones occurred more frequently when using the first boundary condition.