Research Papers

Three-Dimensional Flow Patterns in the Upper Human Airways

[+] Author and Article Information
Katrin Bauer1

 Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Lampadiusstr. 4, 09599 Freiberg, GermanyKatrin.Bauer@imfd.tu-freiberg.de

Alexander Rudert, Christoph Brücker

 Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Lampadiusstr. 4, 09599 Freiberg, Germany


Corresponding author.

J Biomech Eng 134(7), 071006 (Jul 16, 2012) (9 pages) doi:10.1115/1.4006983 History: Received November 15, 2011; Revised May 21, 2012; Posted June 25, 2012; Published July 16, 2012; Online July 16, 2012

Flow dynamics are studied for different ventilation conditions at a three-dimensional model of the human lung airways. The model is based on Horsfield and Weibel data and bifurcates down to the sixth generation. The flow is analyzed numerically and compared to experimental data received from exactly the same model. Numerical and experimental results agree well. Based on this agreement, flow behavior for conventional mechanical ventilation (CMV) as well as for high frequency oscillatory ventilation (HFOV) conditions can be analyzed. Velocity profiles as well as secondary flow structures are investigated during different phases of the unsteady flow. It is shown that the velocity profiles at peak inspiration and expiration are very similar for CMV and HFOV, probably due to too short branch lengths for the development of a frequency-dependent velocity profile. At the flow reversal times, characteristic zones of bidirectional mass flow emerge with increasing amplitude at higher frequencies. Furthermore, secondary flow structures are analyzed. This investigation reveals that the structures only depend on the local curvature and branch orientation, but are not influenced much by the nearby upper or lower branching generations.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

(a) Lung geometry with boundaries and selected cross-section in the first and fifth generation, (b) enlarged view of the grid structure of the inlet boundary (top of the trachea), (c) enlarged view of the grid structure of one of the outlet boundaries (distal end of the sixth generation), 2 × 106 cells, (d) enlarged view of one outlet boundary, 15 × 106 cells

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Figure 2

Velocity contours and profiles during peak inspiration, PIV results (a), numerical results (b), Re = 2000, α = 3

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Figure 3

Vorticity contours during peak expiration, color-coded, where blue indicates clockwise (negative) and red counterclockwise (positive) sense of rotation, respectively. Superposed are cross-sectional streamlines, Re = 1000, α = 5.5, (a) PIV - results, (b) numerical results.

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Figure 4

Velocity profiles for three different Womersley numbers in the first generation (a)–(d) and fifth generation (e)–(h); (a) and (e) peak inspiration; (b) and (f) flow reversal from inspiration to expiration; (c) and (g) peak expiration; (d) and (h) flow reversal from expiration to inspiration

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Figure 5

Iso-contours of the relative velocity magnitude u/umax = 1.3 for peak inspiration (a) and peak expiration (b), Re = 2000, α = 3; cross-sectional cut through the trachea (A-A) and right main branch (B-B) with contour lines of the same velocity magnitude (1.3 m/s) for peak inspiration (c) and peak expiration (d)

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Figure 6

Iso-contours of the y-velocity during flow reversal from expiration to inspiration (a) and from inspiration to expiration (b). Yellow (light) and blue (dark) color indicates positive and negative velocity in the y-direction, respectively. Cut section through the trachea with color-coded vertical velocity component and sectional streamlines during flow reversal from expiration to inspiration (c) and from inspiration to expiration (d).

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Figure 7

Static pressure during one breathing cycle at the tracheal inlet for different Womersley numbers

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Figure 8

Iso-contours of the helicity during peak inspiration (a) and expiration (b). Yellow (light) indicates, counterclockwise rotation; blue (dark), clockwise rotation.

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Figure 9

Average secondary velocity at the cross-section in generation 1 (compare Fig. 1) as function of the peak Reynolds number Re

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Figure 10

Secondary flow structures in selected cross-sections (1–4). Color contours represent the normalized helicity; superposed are sectional streamline patterns.




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