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TECHNICAL PAPERS: Fluids/Heat/Transport

Secondary Velocity Fields in the Conducting Airways of the Human Lung

[+] Author and Article Information
Frank E. Fresconi

Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716fresconi@udel.edu

Ajay K. Prasad

Department of Mechanical Engineering, University of Delaware, Newark, Delaware 19716prasad@udel.edu

J Biomech Eng 129(5), 722-732 (Feb 18, 2007) (11 pages) doi:10.1115/1.2768374 History: Received November 15, 2006; Revised February 18, 2007

An understanding of flow and dispersion in the human respiratory airways is necessary to assess the toxicological impact of inhaled particulate matter as well as to optimize the design of inhalable pharmaceutical aerosols and their delivery systems. Secondary flows affect dispersion in the lung by mixing solute in the lumen cross section. The goal of this study is to measure and interpret these secondary velocity fields using in vitro lung models. Particle image velocimetry experiments were conducted in a three-generational, anatomically accurate model of the conducting region of the lung. Inspiration and expiration flows were examined under steady and oscillatory flow conditions. Results illustrate secondary flow fields as a function of flow direction, Reynolds number, axial location with respect to the bifurcation junction, generation, branch, phase in the oscillatory cycle, and Womersley number. Critical Dean number for the formation of secondary vortices in the airways, as well as the strength and development length of secondary flow, is characterized. The normalized secondary velocity magnitude was similar on inspiration and expiration and did not vary appreciably with generation or branch. Oscillatory flow fields were not significantly different from corresponding steady flow fields up to a Womersley number of 1 and no instabilities related to shear were detected on flow reversal. These observations were qualitatively interpreted with respect to the simple streaming, augmented dispersion, and steady streaming convective dispersion mechanisms.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of three-generational model geometry with nomenclature

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Figure 2

Bifurcation geometry and dimensions for largest bifurcation unit

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Figure 3

Experimental setup

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Figure 4

Variation of secondary flow with Re during inspiration in G1; vorticity contours are used to depict the strength of the secondary flow

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Figure 5

Variation of secondary flow with Re during expiration in G1; vorticity contours are used to depict the strength of the secondary flow

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Figure 6

Variation of secondary velocity with axial location during inspiration for Re=64 in G1; velocity vectors are overlaid on vorticity contours. Reference vector lengths for Xd=0, 1, and 2 are 0.6, 0.2, and 0.2, respectively, of the average primary flow velocity.

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Figure 7

Variation of secondary velocity with axial location during expiration for Re=100 in G1; velocity vectors are overlaid on vorticity contours. Reference vector lengths for Xd=0, 1, and 2 are 0.5, 0.3, and 0.3, respectively, of the average primary flow velocity.

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Figure 8

Variation of secondary velocity with generation/branch during inspiration for Re=64 at Xd=1; velocity vectors are overlaid on vorticity contours. Reference vector lengths are 0.2 of the average primary flow velocity.

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Figure 9

Variation of secondary velocity with generation during expiration for Re=100 at Xd=1; velocity vectors are overlaid on vorticity contours. Reference vector lengths are 0.3 of the average primary flow velocity.

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Figure 10

Variation of secondary velocity during the expiration phase of an oscillatory cycle for Re=100 (corresponding to the peak velocity during the cycle) and α=0.5 at Xd=1 in G1; vorticity contours are used to depict the strength of the secondary flow

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Figure 11

Comparison steady versus oscillatory-peak secondary velocity fields during expiration for Re=100 at Xd=1 in G1. Reference vector lengths are 0.2 of the average primary flow velocity.

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Figure 12

Secondary velocity magnitude as a function of direction, Re, and generation/branch for steady flow at Xd=1

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Figure 13

Secondary velocity magnitude as a function of axial location

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Figure 14

Variation of secondary velocity magnitude during the oscillatory cycle

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