Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session OB: Biofluid Dynamics XIV: Lungs |
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Chair: Ajay Prasad, University of Delaware Room: Tampa Marriott Waterside Hotel and Marina Grand Salon F |
Tuesday, November 21, 2006 12:15PM - 12:28PM |
OB.00001: An experimental study of pulsatile flow through compliant tubes Victoria Sturgeon, Omer Savas, David Saloner An experimental investigation is made into transitional behaviors and instability of oscillatory input flows through elastic tubes, a problem with applications to hemodynamics and flows in the pulmonary system. Sinusoidal input flow is driven through a compliant silicone model in a series of experiments to investigate the effects of wall motion. A novel mechanism allows active control and feedback over the pressure on the tube exterior. By comparing the pressure within and outside of the tube and modifying the exterior pressure accordingly, the tube is inflated in a controlled manner without altering the input flow. In these experiments, the tube wall is deformed sinusoidally with an amplitude of approximately ten percent of its radius. Experiments are conducted using varying values of the parameters $\alpha = a \sqrt{\omega \over \nu}$ and $\beta = \Delta x \sqrt{\omega \over \nu}$ where $a$ is the tube radius, $\omega$ the angular velocity of the input flow, $\nu$ the kinematic viscosity, and $\Delta x$ the cross-stream averaged periodic displacement of a fluid particle undergoing pulsatile motion. For a given $\alpha$, it is found that indications of conditional turbulence appear in this flow through elastic tubes at far lower values of $\beta$ - and thus at lower amplitudes of oscillation - than are reported in the literature for flows through rigid tubing. [Preview Abstract] |
Tuesday, November 21, 2006 12:28PM - 12:41PM |
OB.00002: Multiscale Analysis of a Collapsible Respiratory Airway Samir Ghadiali, E. David Bell, J. Douglas Swarts The Eustachian tube (ET) is a collapsible respiratory airway that connects the nasopharynx with the middle ear (ME). The ET normally exists in a collapsed state and must be periodically opened to maintain a healthy and sterile ME. Although the inability to open the ET (i.e. ET dysfunction) is the primary etiology responsible for several common ME diseases (i.e. Otitis Media), the mechanisms responsible for ET dysfunction are not well established. To investigate these mechanisms, we developed a multi-scale model of airflow in the ET and correlated model results with experimental data obtained in healthy and diseased subjects. The computational models utilized finite-element methods to simulate fluid-structure interactions and molecular dynamics techniques to quantify the adhesive properties of mucus glycoproteins. Results indicate that airflow in the ET is highly sensitive to both the dynamics of muscle contraction and molecular adhesion forces within the ET lumen. In addition, correlation of model results with experimental data obtained in diseased subjects was used to identify the biomechanical mechanisms responsible for ET dysfunction. [Preview Abstract] |
Tuesday, November 21, 2006 12:41PM - 12:54PM |
OB.00003: Numerical Study of Turbulent Laryngeal Jet in the MDCT-based Human Lung Model. Ching-Long Lin, Merryn H. Tawhai, Geoffrey McLennan, Eric A. Hoffman The geometry of the human upper respiratory tract is constructed from x-ray-based multidetector computed tomography (MDCT: Sensation 64) images using in house developed segmentation software. The geometry consists of a mouth piece, the mouth, the oropharynx, the larynx, and up to 6 generations of the intra-thoracic airway tree. We applied a custom-developed Characteristic-Galerkin finite element method, which solves the three-dimensional incompressible Navier-Stokes equations, to study the effect of turbulence on air flow structures in the MDCT-based lung model. In order to gather sufficient data for analysis of turbulence statistics, a constant flow rate of about 320 ml/s at the peak inspiratory phase is imposed at the terminal branches to draw air into the upper respiratory tract. The flow rate yields an average speed of about 2 m/s and a Reynolds number of 1,700 in the trachea. The characteristics of mean velocity and turbulent kinetic energy are analyzed. A curved sheet-like high-speed laryngeal jet with high turbulence intensity is formed in the trachea. Some peak frequencies associated with the jet flow are detected. Their association with turbulent coherent structures is examined. The work is sponsored by NIH Grants R01-EB-005823 and R01-HL-064368. [Preview Abstract] |
Tuesday, November 21, 2006 12:54PM - 1:07PM |
OB.00004: Multi-Scale Human Respiratory System Simulations to Study Health Effects of Aging, Disease, and Inhaled Substances Robert Kunz, Daniel Haworth, Gulkiz Dogan, Andres Kriete Three-dimensional, unsteady simulations of multiphase flow, gas exchange, and particle/aerosol deposition in the human lung are reported. Surface data for human tracheo-bronchial trees are derived from CT scans, and are used to generate three- dimensional CFD meshes for the first several generations of branching. One-dimensional meshes for the remaining generations down to the respiratory units are generated using branching algorithms based on those that have been proposed in the literature, and a zero-dimensional respiratory unit (pulmonary acinus) model is attached at the end of each terminal bronchiole. The process is automated to facilitate rapid model generation. The model is exercised through multiple breathing cycles to compute the spatial and temporal variations in flow, gas exchange, and particle/aerosol deposition. The depth of the 3D/1D transition (at branching generation $n$) is a key parameter, and can be varied. High-fidelity models (large $n$) are run on massively parallel distributed-memory clusters, and are used to generate physical insight and to calibrate/validate the 1D and 0D models. Suitably validated lower-order models (small $n$) can be run on single-processor PC’s with run times that allow model-based clinical intervention for individual patients. [Preview Abstract] |
Tuesday, November 21, 2006 1:07PM - 1:20PM |
OB.00005: Measurement of flow and dispersion in an in-vitro model of a single human alveolus Sudhaker Chhabra, Ajay Prasad The acinar region of the lung consists of alveoli and respiratory bronchioles. Alveoli are the smallest units which participate in gas exchange with the blood. Alveoli can also be exploited as a delivery site for inhaled therapeutic aerosols. While gas transport is governed primarily by diffusion due to the small length scales associated with the acinar region (of the order of 500 microns), the transport and deposition of inhaled aerosol particles is influenced by convective airflow patterns. The current work focuses on measuring the airflow patterns in the acinar region using an in-vitro model of a single alveolus located on a bronchiole. The model consists of a single transparent 5/6$^{th}$ hemispherical oscillating alveolus attached to a rigid circular tube. The alveolus, fabricated from an elastic latex film, is capable of expanding and contracting in phase with the oscillatory flow through the rigid tube. Realistic breathing conditions were achieved by matching Reynolds and Womersley numbers. Particle image velocimetry was used to measure the resulting flow patterns. Data will be presented to show the effect of oscillatory flow in the bronchiole and alveolar wall motion on the flow and dispersion within the alveolus. In particular, measurement of the recirculating flow within the alveolus, and the fluid exchange between the bronchiole and the alveolus provide insights for the transport, mixing and deposition of inhaled aerosols. [Preview Abstract] |
Tuesday, November 21, 2006 1:20PM - 1:33PM |
OB.00006: Secondary flow measurements and passive tracer dispersion in multi-generational models of conducting airways of the lung Frank Fresconi, Ajay Prasad A detailed knowledge of the flow and dispersion within the human respiratory tract is desirable for numerous reasons. Both risk assessments of exposure to toxic particles in the environment and the design of medical delivery systems targeting both lung-specific conditions (asthma, cystic fibrosis, and chronic obstructive pulmonary disease (COPD)) and system-wide ailments (diabetes, cancer, hormone replacement) would profit from such an understanding. The present work features experimental efforts aimed at elucidating the fluid mechanics of the lung. Particle image velocimetry (PIV) and laser induced fluorescence (LIF) measurements of steady and oscillatory flows were undertaken in anatomically accurate models (single and multi-generational) of the conductive region of the lung. PIV results captured primary and secondary velocity fields. LIF allowed visualization of the time-dependent deformation of a passive tracer and also quantified convective dispersion through the usage of a transport profile. [Preview Abstract] |
Tuesday, November 21, 2006 1:33PM - 1:46PM |
OB.00007: Small-Scale Respiratory Flows in a Space-Filling Model of the Pulmonary Acinus Josue Sznitman, Sebastian Schmuki, Reto Sutter, Akira Tsuda, Thomas Roesgen Respiratory flows in the lung periphery are governed by low Reynolds number quasi-Stokes flow induced by the wall motion of sub-millimeter airways marked by the presence of alveoli. Following Fung's model of lung structure (J. Appl. Physiol, 1988), CFD simulations of respiratory flows are investigated in a dichotomous asymmetric three-dimensional space-filling model of a pulmonary acinus. Resulting alveolar flow patterns, induced by kinematic wall motion, are complex and intrinsically three-dimensional. The alveolar flow topology is quasi-steady, due to low Womersley numbers, and largely governed by the ratio of alveolar to ductal flow rates. This ratio describes the interplay between alveolar recirculation, induced by ductal shear flow over the alveolus opening, and alveolar radial flow, induced by the expansion/contraction wall motion. Lagrangian particle tracking of massless particles is conducted over cumulative breathing cycles to investigate the influence of alveolar flows on aerosol kinematics and the existence of irreversible chaotic mixing. Furthermore, our space-filling model is well suited to consider the influence on acinar flows of openings in the alveolar wall between adjacent alveoli (pores of Kohn). [Preview Abstract] |
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