Numerical and Experimental Investigation of Lung Bifurcation Flows

Abstract

The aim of this contribution is to describe a study of pulmonary flows performed using both experimental and computational methods.

The lung consists of a network of bifurcating tubes through which air flows from the trachea through 17 generations of airways where convective processes dominate to the 6 further generations (alveolar zone) where gas exchange occurs and where transport is dominated by molecular diffusion. The part of the lung studied here is the one between generations 12 and 17, just before the alveolar zone,and is characterized by small dimensions and small Reynolds numbers. The main characteristics of this pulmonary flow are: incompressibility, three dimensionality, unsteadiness, laminarity.

Because of its complexity, the problem considered was simplified to consider a single bifurcation. Measurements of velocity were made in a glass model of a bifurcation using Laser Doppler Velocimetry. The geometry of the scale model was chosen to respect geometrical similarity with the physiological data, while dynamics similarity was obtained by using glycerine and varying the velocity at the entry to have the saine Reynolds number. Flow visualisations and results for the velocity field are presented for steady state measurements.

A study of this flow is also being made using a computational method. An existing code was adapted to simulate two dimensional, incompressible, steady flow in a symmetric bifurcation. The code employs finite differences in a curvilinear coordinate system. Results of the first stage of this numerical simulation will be presented and compared with existing data in the literature.