Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session AA: Bio-Fluid Dynamics: Lungs |
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Chair: James Grotberg, University of Michigan Room: Hilton Chicago International Ballroom South |
Sunday, November 20, 2005 8:00AM - 8:13AM |
AA.00001: Effect of oscillatory core-flow on a shear-thinning 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. Flows in the liquid layer are also influenced by the air flow and the rheological properties of the fluid. In this study, we develop a computational model of a liquid-lined tube with an oscillatory core flow: a Newtonian fluid flows through a cylindrical whose inner wall is coated by a shear-thinning fluid. An oscillatory core flow rate is prescribed. The presence of the core flow enhances the initial film growth-rate when compared to no core flow case. As the liquid bulge grows, its axial displacement increases due to the oscillatory core flow. At some point, the film growth-rate decreases and eventually the minimum core radius approaches a non-zero value implying that a liquid plug has not formed. The effect of core flow frequency and amplitude and properties of the film fluid are investigated. This work is supported by NIH grant HL41126, NASA grant NAG3-2740. [Preview Abstract] |
Sunday, November 20, 2005 8:13AM - 8:26AM |
AA.00002: Theoretical Study of Effects of Inertia, Gravity {\&} Interfacial Activities on Steady Plug Propagation in a 2D Channel Ying Zheng, Hideki Fujioka, James Grotberg In many clinical treatments, liquid plugs may form and propagate throughout the pulmonary airways due to the air pressure drop from inspiration and gravity. These will influence the final distribution of liquid in the lung or the success of liquid removal. In this work, we develop a model of propagation of a plug laden with soluble surfactant in a two-dimensional liquid-lined channel oriented at an angle $\alpha $ with respect to the direction of gravity. The equations of motion and surfactant transport are solved numerically using a finite volume method. We study the effect of varying plug propagation speed, U; plug length, Lp; $\alpha $ and surfactant concentration in both Stokes flow limit and finite Reynolds number (Re) regime. The volume ratio, V$_{R}$, of the liquid above and below the center line of the channel, excluding the liquid volume in film region, is calculated to quantify the asymmetric liquid distribution. We find that V$_{R}$ increases with U and Lp for a fixed $\alpha $. V$_{R}$ decreases (increases) with $\alpha $ for $\alpha \le $ ($\ge ) \quad \pi $/2. For finite Re, V$_{R}$ increases with Re for a given value of Lp and $\alpha $. We discuss the effects of U, Lp and $\alpha $ on the wall shear stress and wall pressure. This work is supported by NIH grant HL-41126, HL64373, NSF grant BES-9820967, NASA grant NAG3-2196 and NAG3-2740. [Preview Abstract] |
Sunday, November 20, 2005 8:26AM - 8:39AM |
AA.00003: Development of New Boundary Conditions for Flow in Human Airways Victor Marrero, Kenneth Jansen During recent years much effort has been centered on modeling different aspects of the Human Respiratory System (HRS). Obtaining an accurate description of the structure of the HRS and accurate boundary conditions have been some of the biggest challenges to date in this field. Most of the current CFD models available in the literature focus their attention mainly in the conducting airway zone and make use of a velocity profile boundary condition in the model inlet to emulate the inhalation, and/or exhalation process. While this approach has been used successfully for cardiovascular flows (where the flow rate remains positive over the entire cycle) it is suspect and formally ill posed for flows within the HRS where half of the cycle experiences negative flow rate. To be able to represent more realistic physiological mechanics of the fluid flow in the HRS, new boundary conditions must be developed to more properly account for the oscillatory flow rate. We have developed a constant pressure inlet/outlet boundary conditions as well as deforming outlet boundary conditions (e.g. moving mesh) to produce oscillatory flow within the respiratory system model. Since air behaves as an incompressible fluid in the HRS, as the mesh deforms in an oscillatory manner, an oscillatory flow rate is induced. The simplest version of this approach is akin to a piston-cylinder arrangement with the outlet face being the piston surface. [Preview Abstract] |
Sunday, November 20, 2005 8:39AM - 8:52AM |
AA.00004: Fluid-Structure Interactions and Microparticle Transport in Pulmonary Alveoli Samir Ghadiali, Hannah Dailey The transport of micron-size particles in the lung has important implications for both respiratory disorders and drug delivery systems. During breathing, the expansion of pulmonary alveoli produces sub-ambient pressures that draw airflow into the lung. The fate of inhaled microparticles during breathing will depend on both particle properties and the complex transient flow fields generated by alveolar wall motion. In this study, fluid-structure interaction (FSI) models are used to evaluate the effects of breathing rates, particle size, tissue viscoelasticity and surface tension forces on microparticle transport. In addition to fluid and solid dynamic equations, these models solve a particle equation of motion that includes both Brownian diffusion and gravitational terms. Our results indicate that Brownian diffusion is the dominant mechanism of transport for particles smaller than one micron and that the elastic properties of alveolar tissues can significantly affect particle deposition. Particles larger than 0.5 microns also experience significant gravitational sedimentation, while convection forces become increasingly dominant for larger particles and faster breathing rates. These results may be useful in designing improved drug delivery systems and in establishing new threshold levels for exposure to viral agents. Supported by the NSF and Parker B. Francis Foundation. [Preview Abstract] |
Sunday, November 20, 2005 8:52AM - 9:05AM |
AA.00005: Parallel Computation of Airflow in the Human Lung Model Taehun Lee, Ching-Long Lin, Merryn Tawhai, Eric. A. Hoffman Parallel computations of airflow in the human lung based on domain decomposition are performed. The realistic lung model is segmented and reconstructed from CT images as part of an effort to build a normative atlas (NIH HL-04368) documenting airway geometry over 4 decades of age in healthy and disease-state adult humans. Because of the large number of the airway generation and the sheer complexity of the geometry, massively parallel computation of pulmonary airflow is carried out. We present the parallel algorithm implemented in the custom-developed characteristic-Galerkin finite element method, evaluate the speed-up and scalability of the scheme, and estimate the computing resources needed to simulate the airflow in the conducting airways of the human lungs. It is found that the special tree-like geometry enables the inter-processor communications to occur among only three or four processors for optimal parallelization irrespective of the number of processors involved in the computation. [Preview Abstract] |
Sunday, November 20, 2005 9:05AM - 9:18AM |
AA.00006: Xenon and Helium Gas Transport in the CT-based Human Lung Geometry Ching-Long Lin, Eric Hoffman Stable Xenon (Xe) gas has been used as an imaging agent for decades in its radioactive form, is chemically inert, and has been used as a ventilation tracer in its non radioactive form during computerized tomography (CT) imaging. Magnetic resonance imaging using hyperpolarized Helium (He) gas has also emerged as a powerful tool to study regional lung structure and function. However, the present state of knowledge regarding intra-bronchial Xe and He transport properties is incomplete. As the use of these gases rapidly advances, it has become critically important to understand the nature of their transport properties and to, in the process, better understand regional distribution of respiratory gases. In this study, we applied a custom-developed Characteristic-Galerkin finite element method to study transport of Xe and He in the CT-based human lung geometry, especially emulating the washin and washout processes. The realistic lung model is obtained from multidetector-row CT (MDCT) scanning of supine human subjects with lungs held at TLC and FRC. The simulation results show that the Xe/He washin and washout are governed by either flow instability or stable stratification, depending upon the relative density of resident gas versus inspired gas. [Preview Abstract] |
Sunday, November 20, 2005 9:18AM - 9:31AM |
AA.00007: Modeling and measurements of dispersion in a multi-generational model of the human airways 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) and system-wide ailments (diabetes, cancer, hormone replacement) would profit from such an understanding. The present work features both theoretical and experimental efforts aimed at elucidating the fluid mechanics of the lung. Steady streaming due to dissimilar velocity profiles between inspiration and expiration is addressed theoretically. This model employs a parameterized velocity profile to determine the effect on mass transport in the limit of no mixing and full mixing in the cross-section. Particle image velocimetry and laser induced fluorescence measurements of oscillatory flows in anatomically accurate models (single and multi-generational) of the conductive region of the lung illustrate pertinent flow features. Results are interpreted in the light of physiological applications. [Preview Abstract] |
Sunday, November 20, 2005 9:31AM - 9:44AM |
AA.00008: Three Dimensional Alveolar Flow Phenomena Using a CFD Approach Josue Sznitman, Fabian Heimsch, Thomas Heimsch, Thomas Roesgen Respiratory flows in the lung periphery are characterized by low Reynolds numbers (typically Re$<$1) in sub-millimeter airways marked by the presence of alveoli (gas exchange units). We present for realistic breathing conditions using CFD simulations (CFX-5.7.1), 3D velocity fields and flow patterns induced by the expansion/contraction of alveoli and acinar ducts during oscillatory flow. Based on anatomical data, the alveolus and airway are modeled as a spherical cap connected to a cylindrical duct, both subject to moving wall boundary conditions simulating respiration. The resulting 3D flow patterns are complex and governed by the ratio of the alveolar to ductal flow rates. This ratio describes the interplay between alveolar recirculation, induced by the ductal shear flow over the alveolus opening, and alveolar radial flow, induced by the expansion/contraction motion. Our 3D results are in good agreement with 2D simulations reported in the literature. Although convection mechanisms may transport gas along acinar ducts and deeper into the acinus, velocity fields within alveoli predict that upon gas entering them, transport is then solely dominated by diffusion mechanisms. [Preview Abstract] |
Sunday, November 20, 2005 9:44AM - 9:57AM |
AA.00009: Numerical Analysis of Blood Flow in Arteriole by Lattice Boltzmann Method Dongsik Jang, Marie Oshima In the arteriole with the internal diameter of 10$\sim $100$\mu $m, blood flow has various flow characteristics such as decreasing of a hematocrit, decreasing of the blood viscosity, and axial migration. These phenomena are caused by the interaction between red blood cells (RBCs) and plasma in the arteriole. Thus a numerical method requires to consider such interactions in the arteriole. RBCs in the arteriole deform depending on the shear rate and the hematocrit, which is a volumetric rate of RBCs to blood is relatively high. Since the conventional discritaization method such as FDM or FEM is difficult to track a large amount of deforming particles in the flow, a lattice Boltzmann method (LBM) is used to predict the behavior of the RBCs in the arteriole. In the analysis, the arteriole is assumed as a 2D channel and the RBCs are assumed as the solid particles which are modeled by Ladd's theory or droplets which are modeled by immiscible multi-component LBM. In the Poiseuille flow, each analysis method shows that particles migrate to the equilibrium position. However, the equilibrium positions of the droplets are located closer to the axis than that of the solid particle. In the conclusion, since the droplet can deform as opposed to the solid particle, the droplet can reproduce the behavior of the RBC in the plasma better than the solid particle. [Preview Abstract] |
Sunday, November 20, 2005 9:57AM - 10:10AM |
AA.00010: Pulsatile Flow and Transport of Blood past a Cylinder: Basic Transport for an Artificial Lung. Jennifer R. Zierenberg, Hideki Fujioka, James B. Grotberg The fluid mechanics and transport for flow of blood past a single cylinder is investigated using CFD. This work refers to an artificial lung in which oxygen travels through fibers oriented perpendicularly to the incoming blood flow. A pulsatile blood flow was considered: $U_x =U_0 \left[ {1+A\sin \left( {\omega t} \right)} \right]$, where $U_x $ is the velocity far from the cylinder. The Casson equation was used to describe the shear thinning and yield stress properties of blood. The presence of hemoglobin (i.e. facilitated diffusion) was considered. We examined the effect of $A$, $U_0 $ and $\omega $ on the flow and transport by varying the dimensionless parameters: $A$; Reynolds number, $Re$; and Womersley parameter, $\alpha $. Two different feed gases were considered: pure $O_2 $ and air. The flow and concentration fields were computed for $Re$ = 5, 10, and 40, 0 $\le A\le $ 0.75, $\alpha $ = 0.25, 0.4, and Schmidt number, $Sc$ = 1000. Vortices attached downstream of the cylinder are found to oscillate in size and strength as $\alpha $ and $A$ are varied. Mass transport is found to primarily depend on $Re$ and to increase with increasing $Re$, $\alpha $ and decreasing $A$. The presence of hemoglobin increases mass transport. Supported by NIH HL69420, NSF Fellowship [Preview Abstract] |
Sunday, November 20, 2005 10:10AM - 10:23AM |
AA.00011: Pulsatile Flow and Gas Transport of Blood over an Array of Cylinders Kit Yan Chan, James B. Grotberg In the artificial lung, blood passes through an array of micro-fibers and the gas transfer is strongly dependent on the flow field. The blood flow is unsteady and pulsatile. We have numerically simulated pulsatile flow and gas transfer of blood (modeled as a Casson fluid) over arrays of cylindrical micro-fibers. Oxygen and carbon dioxide are assumed to be in local equilibrium with hemoglobin in blood; and the carbon dioxide facilitated oxygen transport is incorporated into the model by allowing the coupling of carbon dioxide partial pressure and oxygen saturation. The pulsatile flow inputs considered are the sinusoidal and the cardiac waveforms. The squared and staggered arrays of arrangement of the cylinders are considered in this study. Gas transport can be enhanced by: increasing the oscillation frequency; increasing the Reynolds number; increasing the oscillation amplitude; decreasing the void fraction; the use of the cardiac pulsatile input. The overall gas transport is greatly enhanced by the presence of hemoglobin in blood even though the non-Newtonian effect of blood tends to decrease the size and strength of vortices. The pressure drop is also presented as it is an important design parameter confronting the heart. [Preview Abstract] |
Sunday, November 20, 2005 10:23AM - 10:36AM |
AA.00012: Pulsatile Flow Across a Cylinder--An Investigation of Flow in a Total Artificial Lung Yu-chun Lin, Joseph Bull The effect of pulsatility on flow across a single cylinder has been examined experimentally using particle image velocimetry. This work is motivated by the ongoing development of a total artificial lung (TAL), a device which would serve as a bridge to lung transplant. The prototype TAL consists of hollow microfibers through which oxygen-rich gas flows and blood flows around. Flow through the device is provided entirely by right heart and, therefore, is puslatile. The Peclet number of the flow is large and consequently the development of secondary flow affects the resulting gas exchange. The effects of frequency and average flow rate of pulsatile flow around a cylinder were investigated experimentally in a water tunnel and some of the results were compared with preliminary numerical results. Vortices developed behind the cylinder at lower Reynolds numbers in pulsatile flow than steady flow. The results indicate that there are critical values of the Reynolds number between 3 to 5 and Stokes numbers of 0.22, below which vortices were not observed. The findings suggest that higher Stokes and Reynolds numbers within the device could enhance vortex formation. However, this enhanced gas exchange could be at the expense of higher device resistance and increased likelihood of blood trauma. Intelligent TAL design will require consideration of these effects. This work is supported by NIH grant HL69420. [Preview Abstract] |
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