Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session ME: Biofluids IX: Nasal, Lungs and Other Organs |
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Chair: James Grotberg, University of Michigan Room: 101E |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
ME.00001: Flow Visualization Experiments in a 4:1 Scale Model of the Canine Nasal Cavity Michael Hargather, Michael Lawson, Gary Settles An anatomically-correct 4:1 scale model of the canine nasal cavity is used to study flow patterns in the complex nasal airways through dye-streak flow visualization. The nasal cavity geometry was obtained from magnetic resonance imaging (MRI) scans and the model was constructed in sections from a transparent material using a rapid prototyping technique. We believe this model represents the first anatomically-realistic reproduction of the canine nasal cavity, allowing the nasal flowfield to be experimentally studied at a level of detail not previously possible. Olfactory and respiratory flows are observed to take separate paths through the nasal cavity. Respiratory flow through the maxilloturbinates completely bypasses the olfactory region, which amounts to a ``side-sampler.'' A single airway conducts airflow into the olfactory region, whence it slowly filters forward and eventually exits the nasal cavity. The residence time of airflow in the olfactory region varies significantly depending on the specific flowpath taken. The results compare well with computational fluid dynamics (CFD) simulations performed using the same nasal geometry. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
ME.00002: Odorant Transport and Deposition in the Canine Nasal Airways Michael Lawson, Brent Craven, Gary Settles, Eric Paterson The canine nose functions similar to a chromatograph that imposes odorant-specific deposition patterns upon the thin mucus layer covering the nasal cavity. Here we use an anatomically-correct computational fluid dynamics (CFD) model to study airflow and odorant transport from the external environment through the nasal airways to the olfactory receptor layer beneath the mucus. The results show that deposition patterns are primarily influenced by the intricate olfactory flowfield and the odorant solubility in the mucus layer. Highly-soluble odorants are quickly absorbed near the entrance to the olfactory region, and thus do not reach the periphery with significant concentrations. In contrast, insoluble odorants are deposited more evenly and may even exit the olfactory region without being completely absorbed. Predicted odorant deposition patterns correspond with the anatomical organization of olfactory receptors known to occur in keen-scented (macrosmatic) mammals, providing a mechanism that helps explain the excellent olfactory acuity of the dog. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
ME.00003: Alveolar mechanics using realistic acinar models Haribalan Kumar, Ching-Long Lin, Merryn H. Tawhai, Eric A. Hoffman Accurate modeling of the mechanics in terminal airspaces of the lung is desirable for study of particle transport and pathology. The flow in the acinar region is traditionally studied by employing prescribed boundary conditions to represent rhythmic breathing and volumetric expansion. Conventional models utilize simplified spherical or polygonal units to represent the alveolar duct and sac. Accurate prediction of flow and transport characteristics may require geometries reconstructed from CT-based images and serve to understand the importance of physiologically realistic representation of the acinus. In this effort, we present a stabilized finite element framework, supplemented with appropriate boundary conditions at the alveolar mouth and septal borders for simulation of the alveolar mechanics and the resulting airflow. Results of material advection based on Lagrangian tracking are presented to complete the study of transport and compare the results with simplified acinar models. The current formulation provides improved understanding and realization of a dynamic framework for parenchymal mechanics with incorporation of alveolar pressure and traction stresses. [Preview Abstract] |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
ME.00004: On boundary-layer and free-shear resistances in the human airways Jiwoong Choi, Ching-Long Lin, Merryn Tawhai, Eric Hoffman The airway resistance has been reported to be greater on expiration than inspiration. To understand the underlying mechanism, we perform large eddy simulation of airflow in the 3D CT-resolved 7-generation airways constrained by physiologically-consistent lobar ventilation. The dimensionless viscous pressure drops in all the airway segments exhibit a similarity behavior proportional to \textit{(ReD/L)}$^{n}$ with the average optimal values of 1.4 and 1.6 for inspiration and expiration, respectively, where \textit{Re} is the Reynolds number, and $D$ and $L$ are the respective average diameter and length of an airway segment. It is found that the dissipations in the boundary layer as well as the free-shear core flow contribute to the airway resistance, thus the n value. Flow is partitioned to examine the roles played by the boundary layer and the free-shear flow, respectively. A hypothesis is proposed to explain higher airway resistance on expiration. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
ME.00005: Steady propagation of Bingham plugs in 2D channels Parsa Zamankhan, Shuichi Takayama, James Grotberg The displacement of the yield-stress liquid plugs in channels and tubes occur in many biological systems and industrial processes. Among them is the propagation of mucus plugs in the respiratory tracts as may occur in asthma, cystic fibrosis, or emphysema. In this work the steady propagation of mucus plugs in a 2D channel is studied numerically, assuming that the mucus is a pure Bingham fluid. The governing equations are solved by a mixed-discontinuous finite element formulation and the free surface is resolved with the method of spines. The constitutive equation for a pure Bingham fluid is modeled by a regularization method. Fluid inertia is neglected, so the controlling parameters in a steady displacement are; the capillary number, Ca, Bingham number ,Bn, and the plug length. According to the numerical results, the yield stress behavior of the plug modifies the plug shape, the pattern of the streamlines and the distribution of stresses in the plug domain and along the walls in a significant way. The distribution along the walls is a major factor in studying cell injuries. This work is supported through the grant NIH HL84370. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
ME.00006: Flow through flexible cylinders inspired by the endothelial glycocalyx Lauren Cooper, Daniel Fovargue, Laura Miller Inspired by the recent shift in hypertension research, we present a new computational model to better examine blood flow induced shear stress in the endothelial surface layer (ESL). The ESL is the luminal side barrier between blood and the endothelial cells that line the vessel wall and has been of interest due to its function as a mechanotransducer.\footnote{Squire, J. M., Chew, M., Nneji, G., Neal, C., Barry, J. {\&} Michel, C. C., 2001. Quasi-periodic substructure in the microvessel endothelial glycocalyx: a possible explanation for molecular filtering? J. Struct. Bio. 136, 239-255.} Further, it is believed that shear stress seen by the ESL, induced by blood flow, is converted to chemical responses such as blood pressure regulation. We utilize the Immersed Boundary method to simulate blood flow through a vessel and examine the shear stress at the ESL over different heights and flexibilities. We compare our results in the Reynolds number regime of a canine capillary with previous computational models\footnote{Weinbaum, S., Tarbell, J., Damiano, E., 2000. The Structure and Function of the Endothelial Glycocalyx Layer. Pfl\"{u}gers Arch. -- Eur. J. Physiol. 440, 653--666.} and experimental results. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
ME.00007: High-frequency self-excited oscillations in collapsible tube flows Robert J. Whittaker, Sarah L. Waters, Oliver E. Jensen, Jonathan Boyle, Matthias Heil Experiments show that steady flow along an elastic-walled tube can become unstable to large-amplitude oscillations involving both the tube wall and the fluid. We consider a ``Starling resistor'' setup - a finite length elastic tube attached to rigid end sections, through which an axial flow is driven by either a steady flux at the downstream end or a steady pressure drop between the ends. We present a theoretical analysis of small-amplitude high-frequency long-wavelength oscillations. We first consider the fluid mechanics (with prescribed wall oscillations) and then the solid mechanics (to derive an appropriate tube law) in isolation. The two strands are then combined to investigate the full 3D fluid--structure interaction problem for self-excited oscillations. We determine the form of the normal modes and obtain expressions for the growth rate and frequency of the oscillations. The predictions from our modeling are compared with numerical simulations performed using the oomph-lib library. [Preview Abstract] |
Tuesday, November 24, 2009 9:31AM - 9:44AM |
ME.00008: Control volume based hydrocephalus research; a phantom study Benjamin Cohen, Abram Voorhees, Joseph Madsen, Timothy Wei Hydrocephalus is a complex spectrum of neurophysiological disorders involving perturbation of the intracranial contents; primarily increased intraventricular cerebrospinal fluid (CSF) volume and intracranial pressure are observed. CSF dynamics are highly coupled to the cerebral blood flows and pressures as well as the mechanical properties of the brain. Hydrocephalus, as such, is a very complex biological problem. We propose integral control volume analysis as a method of tracking these important interactions using mass and momentum conservation principles. As a first step in applying this methodology in humans, an \textit{in vitro} phantom is used as a simplified model of the intracranial space. The phantom's design consists of a rigid container filled with a compressible gel. Within the gel a hollow spherical cavity represents the ventricular system and a cylindrical passage represents the spinal canal. A computer controlled piston pump supplies sinusoidal volume fluctuations into and out of the flow phantom. MRI is used to measure fluid velocity and volume change as functions of time. Independent pressure measurements and momentum flow rate measurements are used to calibrate the MRI data. These data are used as a framework for future work with live patients and normal individuals. Flow and pressure measurements on the flow phantom will be presented through the control volume framework. [Preview Abstract] |
Tuesday, November 24, 2009 9:44AM - 9:57AM |
ME.00009: The Relation between Peristaltic and Segmental Contraction, Mixing, and Absorption in the Small Intestine Gino Banco, James Brasseur, Yanxing Wang, Amit Ailiani, Thomas Neuberger, Andrew Webb The physiology and mechanics of the small intestine originates with lumen-scale fluid motions generated by enterically controlled muscle wall contractions. Although complex in appearance, we have shown with principle component decomposition of gut motion from a rat model that simpler component structure may integrate to produce basic peristaltic and segmental motions. To couple these measured modes with fluid mixing and nutrient absorption we have developed 2-D and axisymmetric models of the gut using the lattice-Boltzmann framework with scalar and second order moving boundary conditions. Previous models indicated that peristalsis is detrimental to absorption and therefore that gut motility is likely bimodal, transitioning between peristalsis and segmental modes to optimize the transport of chyme vs. nutrient absorption. However we have since discovered that more complex control is possible due to potential transitions between ``trapped'' vs. ``nontrapped'' peristaltic fluid motions, depending on occlusion ratio. These transitions lead to an important distinction between 2-D and axisymmetric models and indicate that gut motility may be more finely controlled than previously thought. [Supported by NSF] [Preview Abstract] |
Tuesday, November 24, 2009 9:57AM - 10:10AM |
ME.00010: An Integrative Model of Excitation Driven Fluid Flow in a 2D Uterine Channel Charles Maggio, Lisa Fauci, John Chrispell We present a model of intra-uterine fluid flow in a sagittal cross-section of the uterus by inducing peristalsis in a 2D channel. This is an integrative multiscale computational model that takes as input fluid viscosity, passive tissue properties of the uterine channel and a prescribed wave of membrane depolarization. This voltage pulse is coupled to a model of calcium dynamics inside a uterine smooth muscle cell, which in turn drives a kinetic model of myosin phosphorylation governing contractile muscle forces. Using the immersed boundary method, these muscle forces are communicated to a fluid domain to simulate the contractions which occur in a human uterus. An analysis of the effects of model parameters on the flow properties and emergent geometry of the peristaltic channel will be presented. [Preview Abstract] |
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