The effect of inlet velocity profile on the bifurcation COPD airway flow.

The effect of inlet velocity profile on the flow features in obstructed airways is investigated in this study. In reality, the inlet velocity distributions on such models, which are extracted from medial branches of natural human lung, should be neither uniform, nor symmetric parabolic, but skewed-parabolic due to having been skewed by the upper carina ridges. Four different three-dimensional three-generation models based on the 23 generations model of Weibel have been considered, respectively. The fully three-dimensional incompressible laminar Navier-Stokes equations and continuity equation have been solved using CFD solver on unstructured tetrahedral meshes. To reduce the complexity of the simulations, only one Reynolds number of 900 was used in this calculation. Four types of inlet boundary conditions, namely uniform, parabolic, positive-skewed parabolic (skewed to the positive x-direction), and negative-skewed parabolic, were imposed on the obstructed airway models, which were considered to be obstructed at either the second generation or the third generation airways, respectively. The results show that the inlet velocity profile has significant influence on the flow patterns, mass distributions, and pressure drops in either the symmetric model, or the three obstructed models. The three generation airways may not be enough to study the bifurcation flow in chronic obstructive pulmonary disease (COPD) airways, and a four-generation or more airway model is necessary to get better predictive results.