Flow structures and particle deposition patterns in double-bifurcation airway models. Part 1. Air flow fields

Abstract

The understanding and quantitative assessment of air flow fields and local micron-particle wall concentrations in tracheobronchial airways are very important for estimating the health risks of inhaled particulate pollutants, developing algebraic transfer functions of global lung deposition models used in dose-response analyses, and/or determining proper drug-aerosol delivery to target sites in the lung. In this paper (Part 1) the theory, model geometries, and air flow results are provided. In a companion paper (Part 2, Comer et al. 2001), the history of particle deposition patterns and comparisons with measured data sets are reported. Decoupling of the naturally dilute particle suspension makes it feasible to present the results in two parts.Considering a Reynolds number range of 500 [les ] ReD [les ] 2000, it is assumed that the air flow is steady, incompressible and laminar and that the tubular double bifurcations, i.e. Weibel's generations G3–G5, are three-dimensional, rigid, and smooth with rounded as well as sharp carinal ridges for symmetric planar, and just rounded carinas for 90° non-planar configurations. The employed finite-volume code CFX (AEA Technology) and its user-enhanced FORTRAN programs were validated with experimental velocity data points for a single bifurcation. The resulting air flow structures are analysed for relatively low (ReD = 500) and high (ReD = 2000) Reynolds numbers. Sequential pressure drops due to viscous effects were calculated and compared, extending a method proposed by Pedley et al. (1977). Such detailed results for bifurcating lung airways are most useful in the development of global algebraic lung models.

Fluid–structure interaction in lower airways of CT‐based lung geometries

“…Studies on symmetrical Weibel models revealed a Dean-flow pattern in the daughter tube while a skewed swirl pattern was observed in the grandchild tube, see, e.g. Comer et al [5,6] and Nowak et al [17] although we know that the flow patterns in real lungs are more complex.…”

Interplay between Geometry and Flow Distribution in an Airway Tree

“…At large Re, the M-shape is revealed and, as expected, the lower the Re, the closer the profile is to parabolic flow. The smaller variation of Σ for Re > 250 can be explained by the presence of a secondary flow [13].…”

“…Unambiguous experimental and numerical evidences of inertial effects have been observed in several studies on flow though branched structures, with special emphasis on the bronchial tree [2][3][4][5][6][7][8][9][10][11][12][13][14]. Such phenomena exists in real lungs but they are more simple to study in a symmetric geometry [15,16].…”

“…Of course, if the flow distribution is found uniform although the geometry is "imperfect", the following question would naturally arise [25]: what are the physiological regulation mechanisms that can compensate the flow non-uniformity due to inertial effects? In addition, the fluid dynamics studied here is certainly relevant to understand particle deposition in the airway tree [13], a problem of crucial importance both from the physiologic and the therapeutic points of view.…”

Multi-branching flows from one mother tube to many daughters or to a network

“…Several theoretical conjectures remain largely untested, while direct computation has only given solutions either accurately over a few generations or with limited detail over more generations (see Hademenos et al 1996;Pries et al 1998;Goldman & Popel 2000;Smith & Jones 2003). Related branching or network studies have been conducted with some success by Handa et al (1993), Miyasaka et al (1993), Pedley et al (1994), Gatlin et al (1995), Young et al (1996), Gao et al (1997), Hademenos & Massoud (1997), Wilquem & Degrez (1997), Zhai et al (1997), Pries et al (1998), Brada & Kitchen (2000), Kassab et al (2000), Lorthois et al (2000), McEvoy et al (2000), Cassidy et al (2001) and Comer et al (2001). The presence of an arteriovenous malformation in a cranial system eventually requires study of the application of type I within the wider framework of an application similar to type II.…”