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Research Papers: Flows in Complex Systems

A Method for Three-Dimensional Navier–Stokes Simulations of Large-Scale Regions of the Human Lung Airway

[+] Author and Article Information
D. Keith Walters

Department of Mechanical Engineering, Mississippi State University, CAVS SimCenter, P.O. Box ME, Mississippi State, MS 39762walters@me.msstate.edu

William H. Luke

Department of Mechanical Engineering, Mississippi State University, CAVS SimCenter, P.O. Box ME, Mississippi State, MS 39762whl30@msstate.edu

J. Fluids Eng 132(5), 051101 (Apr 27, 2010) (8 pages) doi:10.1115/1.4001448 History: Received June 11, 2009; Revised March 08, 2010; Published April 27, 2010; Online April 27, 2010

A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented. The new approach provides a means for detailed resolution of the flow features via three-dimensional Navier–Stokes CFD simulation without the need for full resolution of the entire flow geometry, which is well beyond the reach of available computing power now and in the foreseeable future. The method is based on a finite number of flow paths, each of which is fully resolved, to provide a detailed description of the entire complex small-scale flowfield. A stochastic coupling approach is used for the unresolved flow path boundary conditions, yielding a virtual flow geometry that allows accurate statistical resolution of the flow at all scales for any set of flow conditions. Results are presented for multigenerational lung models based on the Weibel morphology and the anatomical data of Hammersley and Olson (1992, “Physical Models of the Smaller Pulmonary Airways,” J. Appl. Physiol., 72(6), pp. 2402–2414). Validation simulations are performed for a portion of the bronchiole region (generations 4–12) using the flow path ensemble method, and compared with simulations that are geometrically fully resolved. Results are obtained for three inspiratory flowrates and compared in terms of pressure drop, flow distribution characteristics, and flow structure. Results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by up to an order of magnitude.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Illustration of the generational description for a dichotomous branching network

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Figure 2

Eight-generation model of the bronchial region based on the (a) Weibel (1) lung morphology, comprised of (b) successive parent-daughter branching units

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Figure 3

Flow path ensemble models obtained by truncating the eight-generation airway tree shown in Fig. 2: (a) 4-path ensemble and (b) 16-path ensemble

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Figure 4

Example of the stochastic coupling method for unresolved boundary conditions. The resolved pressure at location A is mapped to the unresolved outlet location B, C is mapped to D, etc.

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Figure 5

Illustration of the virtual geometry created by stochastic coupling of unresolved boundary conditions. The real 4-path geometry is shown in (a), and the virtual geometry in (b).

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Figure 6

(a) Fine mesh and (b) coarse mesh used in mesh resolution study. Validation test case results were obtained with the resolution level showed in (b).

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Figure 7

Illustration of mesh resolution near terminal outlets for all validation cases

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Figure 8

Predicted pressure contours on airway walls using stochastically coupled boundary conditions: (a) full geometry; (b) 4-path ensemble; (c) 16-path ensemble

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Figure 9

Predicted pressure contours on airway walls using a priori pressure boundary conditions: (a) full geometry; (b) 4-path ensemble; (c) 16-path ensemble

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Figure 10

Velocity magnitude contours and in-plane velocity vectors: (a) generation 9, full geometry; (b) generation 9, 16-path FPE model; (c) generation 11, full geometry; (d) generation 11, 16-path FPE model

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Figure 11

Dimensionless pressure drop versus inlet mass flow rate for validation test cases

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Figure 12

Predicted pressure contours on airway walls for the high-Re case: (a) full geometry; (b) 4-path ensemble with stochastically coupled BCs; (c) 4-path ensemble with uniform pressure BCs

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