Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session GD: Biofluids VII |
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Chair: Michael Plesniak, Polytechnic University Room: Salt Palace Convention Center 151 A-C |
Monday, November 19, 2007 10:30AM - 10:43AM |
GD.00001: Patterns of Mixing in the Alveolar Region of the Human Lungs Haribalan Kumar, Ching-Long Lin, Merryn H. Tawhai, Geoffrey Mclennan, Eric A. Hoffman The air-flow characteristics in the alveolar region of the human lungs is investigated to understand the mixing patterns at low Reynolds number and their relationship to transport and deposition of pharmaceutical and pollutant particles. 2D and 3D realistic honeycomb-like polygonal geometries are constructed to represent alveolar sacs. An in-house characteristic-Galerkin finite element code in an ALE framework is utilized to simulate flow in the acinar airways ranging from the 17$^{th}$ to 23$^{rd}$ generation (with Re=1-0.01). The flow is unsteady and is driven by physiologically rhythmic wall motion. Lagrangian-based numerical visualization is used to provide a complete description of the dynamics. Results in the form of material advection (dye or blob) and stretch rate are presented. Time averaged mixing estimates are used to analyze different breathing frequencies and patterns. [Preview Abstract] |
Monday, November 19, 2007 10:43AM - 10:56AM |
GD.00002: Comparison of Air flow in CT-Based Rigid and Flexible Human Airway Models Guohua Xia, Ching-long Lin, Merryn H. Tawhai, Eric A. Hoffman The air flow characteristics in a CT-based human airway bifurcation with rigid and flexible walls are investigated numerically. An in-house 3D fluid-structure interaction solver is applied to simulate the flow at different Reynolds number and airway wall stiffness. For the flexible wall case, the bending curvature at bifurcation increases with softening wall stiffness during inspiration phase, resulting in enhanced secondary flow motion and velocity skewedness. As the Reynolds number increases, the airway wall deformation increases and the secondary flow becomes more prominent. It is also found that the fluid shear stress on the rigid airway wall is stronger than that on the flexible airway wall. It implies that the formation of fibrosis in the lungs, which hardens the airway wall and restrains the airway motion, has a tendency to increase wall shear stress and subsequently damage the lung tissue. [Preview Abstract] |
Monday, November 19, 2007 10:56AM - 11:09AM |
GD.00003: Airway Resistance and Energy Budget of Airflow in a CT-Based Human Lung Model. Ching-Long Lin, Merryn H. Tawhai, Eric A. Hoffman An in-house characteristic-Galerkin finite element code is utilized to study airway resistance and energy budget of airflow in 5-7 generations of a CT-based human lung model. The energy budget of airflow in the trachea and main bronchi is further analyzed and compared with Pedley's airway resistance formula. The results show that most airways exhibit an asymptotic relationship of pressure drop proportional to mass flux with a power varying from 2 to 1.6. The maximum predicted airway resistance is found at the fourth airway generation with a value of 0.09 cm-H2O/l/s at peak inspiration. This is in excellent agreement with existing experimental data. According to the pressure drop-mass flux relationship, the five lobes have similar collective flow characteristics in the studied normal subject. The effect of turbulent laryngeal jet on the energy budget and airway resistance is also discussed. [Preview Abstract] |
Monday, November 19, 2007 11:09AM - 11:22AM |
GD.00004: Blood Flow and Oxygen Transport Past an Elliptical Fiber in an Artificial Lung Jennifer Zierenberg, Hideki Fujioka, Ronald Hirschl, Robert Bartlett, James Grotberg Artificial lungs are currently being developed to serve as bridges to lung transplantation with circular fibers, which are permeable to oxygen, used as the transport surface. Blood flows across the fibers while oxygen flows through the fiber lumen. The present work investigates the novel approach of using elliptical fibers as the transport medium. Steady blood flow, modeled as a Casson fluid, and oxygen transport over a single fiber are investigated for varying elliptic aspect ratios ($Ar$=minor radius/major radius) and orientations to flow ($\phi$). The parameters investigated are $Re = 1, 5, 10$; $Ar = 0.25, 0.5, 0.75, 1$; $\phi = 0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$, $90^{\circ}$; and $Sc = 1000$. The Casson properties of blood decrease the size and strength of recirculation(s) which when present are attached to the downstream side of the fiber. A maximum decrease of $24\%$ in drag and an increase of $10\%$ in transport are observed for $Re = 5$, $Ar = 0.25$ and $\phi = 0^{\circ}$ as compared to the circular fiber. The elliptic properties can thus aid in the design of artificial lungs. [Preview Abstract] |
Monday, November 19, 2007 11:22AM - 11:35AM |
GD.00005: On the Effects of Intra- and Inter-Subject Variabilities on Human Inspiratory Flow Jiwoong Choi, Ching-Long Lin, Merryn H. Tawhai, Eric A. Hoffman The effects of intra- and inter-subject variabilities on airflow patterns in the human central airways are investigated using large-eddy simulation (LES). The anatomical airway models are reconstructed from multi-detector row computed tomography (MDCT) image data. The intra-subject study considers four models of the same human subject, including complete, partial, and no upper respiratory tract. Either pressure or velocity boundary conditions are specified at the mouth, mid pharynx, supraglottis, and tracheal entrance, respectively, with two different flow rates. The inter-subject study considers upper and intra-thoracic airways (up to 6 generations) of two human subjects. LES captures the turbulent laryngeal jet formed at the vocal cords. It is found that the use of a complete upper respiratory tract as well as the anatomically realistic airway geometry is essential to correctly reproduce the laryngeal jet behavior and turbulent coherent structures in particular. [Preview Abstract] |
Monday, November 19, 2007 11:35AM - 11:48AM |
GD.00006: The Influence of Non-Newtonian Properties on Steady Plug Propagation in a 2D Channel Ying Zheng, Hideki Fujioka, James B. Grotberg In obstructive pulmonary diseases, the lung's small airways can be closed by the formation of liquid plugs, which obstruct the airflow and propagate throughout the pulmonary airways due to the air pressure drop. The liquid in the lung airways (so-called mucus) has non-Newtonian characteristics with shear thinning and yield stress. In this work, we numerically studied the plug propagation of non-Newtonian fluid laden with soluble surfactant in a two-dimensional liquid-lined channel. The non-Newtonian behavior is described by a power-law model with shear thinning characteristics similar as mucus, of the form $\mu =K\dot {\gamma }^{n-1}$, where $\dot {\gamma }$ is the shear rate and n$<$=1 is the power law index. For a given propagation speed, the deposited film thickness and pressure drop across the plug increase with decreasing n. Also, the wall pressure and shear stress increases with the decreases of n, which could lead to an increase of the damage of the cells lining the airways. This is mainly due to an increase in local viscosity in the plug domain. The effects of yield stress, plug speed, plug length and surfactant concentrations on plug flow pattern and wall stress distribution are discussed. This work is supported by NIH grant HL84370, NASA grant NAG3-2740 and NASA NBEI grant NNC04AA21A. [Preview Abstract] |
Monday, November 19, 2007 11:48AM - 12:01PM |
GD.00007: Effect of oscillatory core-flow on a viscoelastic fluid layer coating the inner surface of a tube. Hideki Fujioka, David Halpern, James B. Grotberg Surface tension on an air-liquid interface induces liquid flows, which may cause the lung's airways to close due to the formation of a liquid plug as a result of drainage of the liquid lining coating the airways. The stability of the liquid layer is also influenced by the air core flow as well as the rheological properties of the liquid. In this study, we develop a computational model of a liquid-lined tube with an oscillatory core flow along the axis of the tube: a Newtonian fluid flows through a cylinder whose inner wall is coated by an upper-convective Maxwell fluid. When no core flow is present, the viscoelastic fluid layer grows faster and closure times are shorter than a Newtonian fluid layer with the same viscosity. When an oscillatory core flow is present, the liquid bulge that develops after the initial growth translates back and forth along the tube axis with an amplitude that increases with elasticity. If this amplitude is large enough, the minimum core radius approaches a non-zero value implying that a liquid plug has not formed. The effects of core flow frequency and amplitude on this instability are discussed. [Preview Abstract] |
Monday, November 19, 2007 12:01PM - 12:14PM |
GD.00008: Effect of Phase Lag on Fluid Flow and Particle Dispersion in a Single Human Alveolus Sudhaker Chhabra, Ajay Prasad The human lung can be divided into (1) the conducting airways, and (2) the acini. The acini are responsible for gas exchange and consist of alveoli and bronchioles. The acini are useful delivery sites for inhaled therapeutic aerosols. In normal lung function the alveolus expands and contracts in phase with the bronchiole airflow oscillation. Lung diseases such as emphysema compromise the elasticity of the lung. Consequently, the alveolus may not oscillate in-phase with the oscillating bronchiole airflow. We have previously studied flow and particle transport in an alveolus for in-phase flow. The current work focuses on measuring out-of-phase airflow patterns and particle transport in an \textit{in-vitro} model of a single expanding/contracting human alveolus. The model consists of a transparent, elastic, oscillating alveolus (represented by a 5/6th hemisphere) attached to a rigid circular tube. Realistic tidal breathing conditions were achieved by matching Reynolds and Womersley numbers. Flow patterns were measured using PIV; these velocity maps were subsequently used to calculate particle transport and deposition on the alveolar wall. [Preview Abstract] |
Monday, November 19, 2007 12:14PM - 12:27PM |
GD.00009: Infomechanical specializations for prey capture in knifefish Malcolm MacIver, Neelesh Patankar, Oscar Curet, Anup Shirgaonkar How does an animal's mechanics and its information acquisition system work together to solve crucial behavioral tasks? We examine this question for the black ghost weakly electric knifefish (\textit{Apteronotus albifrons}), which is a leading model system for the study of sensory processing in vertebrates. These animals hunt at night by detecting perturbations of a self-generated electric field caused by prey. While the fish searches for prey, it pitches at $\approx $30\r{ }. Fully resolved Navier-Stokes simulations of their swimming, which occurs through undulations of a long ribbon-like fin along the bottom edge of the body, indicates that this configuration enables maximal thrust while minimizing pitch moment. However, pitching the body also increases drag. Our analysis of the sensory volume for detection of prey shows this volume to be similar to a cylinder around the body. Thus, pitching the body enables a greater swept volume of scanned fluid. Examining the mechanical and information acquisition demands on the animal in this task gives insight into how these sometimes conflicting demands are resolved. [Preview Abstract] |
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