Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D15: Focus Session: Respiratory Bio-Fluid Dynamics I |
Hide Abstracts |
Chair: James Grotberg, University of Michigan Room: 3022/3024 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D15.00001: Impact of the Equation of State in Models for Surfactant Spreading Experiments Rachel Levy Pulmonary surfactant spreading models often rely on an equation of state relating surfactant concentration to surface tension.~ Mathematically, these models have been analyzed with simple functional relationships.~ However, to model an experiment with a given fluid and surfactant, a physically meaningful equation of state can be derived from experimentally obtained isotherms.~ We discuss the comparison between model and experiment for NBD-PC lipid (surfactant) spreading on glycerol for an empirically-determined equation of state, and compare those results to simulations with traditionally employed functional forms.~ In particular we compare the timescales by tracking the leading edge of surfactant, the central fluid height and dynamics of the Marangoni ridge.~ We consider both outward spreading of a disk-shaped region of surfactant and the hole-closure problem in which a disk-shaped surfactant-free region self-heals. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D15.00002: Large-eddy Simulation of Heat and Water Vapor Transfer in CT-Based Human Airway Models Dan Wu, Merryn Tawhai, Eric Hoffman, Ching-Long Lin We propose a novel imaging-based thermodynamic model to study local heat and mass transfers in the human airways. Both 3D and 1D CFD models are developed and validated. Large-eddy simulation (LES) is adopted to solve 3D incompressible Navier-Stokes equations with Boussinesq approximation along with temperature and water vapor transport equations and energy-flux based wall boundary condition. The 1D model provides initial and boundary conditions to the 3D model. The computed tomography (CT) lung images of three healthy subjects with sinusoidal waveforms and minute ventilations of 6, 15 and 30 L/min are considered. Between 1D and 3D models and between subjects, the average temperature and water vapor distributions are similar, but their regional distributions are significantly different. In particular, unlike the 1D model, the heat and water vapor transfers in the 3D model are elevated at the bifurcations during inspiration. Moreover, the correlations of Nusselt number (Nu) and Sherwood number (Sh) with local Reynolds number and airway diameter are proposed. In conclusion, use of the subject-specific lung model is essential for accurate prediction of local thermal impacts on airway epithelium. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D15.00003: Development of a 3D to 1D Particle Transport Model to Predict Deposition in the Lungs Jessica M. Oakes, Celine Grandmont, Shawn C. Shadden, Irene E. Vignon-Clementel Aerosolized particles are commonly used for therapeutic drug delivery as they can be delivered to the body systemically or be used to treat lung diseases. Recent advances in computational resources have allowed for sophisticated pulmonary simulations, however it is currently impossible to solve for airflow and particle transport for all length and time scales of the lung. Instead, multi-scale methods must be used. In our recent work, where computational methods were employed to solve for airflow and particle transport in the rat airways (Oakes et al. (2014), Annals of Biomedical Engineering, 42: 899-914), the number of particles to exit downstream of the 3D domain was determined. In this current work, the time-dependent Lagrangian description of particles was used to numerically solve a 1D convection-diffusion model (trumpet model, Taulbee and Yu (1975), Journal of Applied Physiology, 38: 77-85) parameterized specifically for the lung. The expansion of the airway dimensions was determined based on data collected from our aerosol exposure experiments (Oakes et al. (2014), Journal of Applied Physiology, 116: 1561-8). This 3D-1D framework enables us to predict the fate of particles in the whole lung. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D15.00004: Oscillatory Flow in the Human Airways from the Mouth through Several Bronchial Generations Andrew Banko, Filippo Coletti, Chris Elkins, John Eaton The time-varying flow is studied experimentally in an anatomically accurate model of the human airways from the mouth through the fourth to eighth generation of the bronchi. The airway geometry is obtained from the CT scan of a healthy adult male of normal height and build. The three-component, three-dimensional mean velocity field is obtained throughout the entire model using phase-locked magnetic resonance velocimetry. A pulsatile pump drives a sinusoidal waveform (inhalation and exhalation) with frequency and stroke-length such that the mean trachea Reynolds number at peak inspiration is Re $=$ 4200 and the Womersley number is $\alpha =$ 7. This represents a regime of moderate exertion. Integral parameters are defined to quantify the degree of velocity profile non-uniformity (which correlates with axial dispersion) and secondary flow strength (which correlates with lateral dispersion). It is found that the streamwise momentum flux and secondary flow strength increase and decrease in proportion throughout most of the breathing cycle. On the other hand, the strength of secondary flows during the 10{\%} of the breathing cycle surrounding flow reversal remains approximately half of that at peak inspiration while the streamwise momentum flux goes to zero. The strong and persistent secondary flows have important implications for dispersion of scalar or particulate contaminants in the lungs. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D15.00005: Coupling of the interfacial and bulk flow in a knife-edge surface viscometer Aditya Raghunandan, Christopher Tilger, Amir Hirsa, Juan Lopez After more than 50 years of investigating how to measure surface (excess) shear viscosity, it remains a controversial issue. The complications stem from the fact that to measure a viscous response the system needs to be flowing, and for a surface film on a liquid substrate this means that the liquid in the bulk will also be flowing. Macroscale measurements, which generally provide greater accuracy, are often made at Reynolds numbers that are large enough for inertia to be non-negligible. However the theoretical models against which the measurements are compared have so far failed to properly account for the coupling. Results will be presented from a numerical study on the coupling between the interfacial and bulk flow. Also, experimental results will be presented for the lung surfactant component DPPC. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D15.00006: An exact solution for Stokes flow in an infinite channel with permeable walls Gregory Herschlag, Jian-Guo Liu, Anita Layton We derive an exact solution for Stokes flow in an infinite channel with permeable walls. We assume that at the channel walls, the normal component of the fluid velocity is described by Darcy's law and the tangential component of the fluid velocity is described by the no slip condition. The pressure exterior to the channel is assumed to be constant. We verify that in the limit of small permeability, Poiseuille flow is recovered to leading order, and demonstrate that our exact result agrees with previous approximate results in this limit. By comparing our solution to existing assumptions on inlet profiles in the literature, we find that although the error is small, Poiseuille and Berman flow do not provide correct inlet conditions. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D15.00007: Droplets and modes of respiratory disease transmission Lydia Bourouiba Direct observation of violent expirations such as sneezes and coughs events reveal that such flows are multiphase turbulent buoyant clouds with suspended droplets of various sizes. The effects of ambient conditions indoors, such as moisture and temperature, coupled with the water content of such clouds are key in shaping the pathogen footprint emitted by potentially sick individuals. Such pathogen footprint can change the patterns of respiratory disease transmission. We discuss how the fluid dynamics of violent expirations can help inform how. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D15.00008: Biasing left-right particle distribution via sideways bending of the upper body Jorge A. Bernate, Eleanor Lin, Rebecca Fahrig, Carlos Milla, Gianluca Iaccarino, Eric S.G. Shaqfeh The ability to target therapeutic aerosols to specific regions of the lungs would result in more effective treatment of localized pulmonary diseases and may also prove beneficial in systemic delivery via the airways. Previous computational and experimental studies have shown that large particles disproportionately enter the left lung. The observed uneven distribution occurs because the trachea bends to the right just before the first bifurcation, causing particles with sufficient inertia to enter the left main bronchus. Via CT imaging, we have shown that it is possible to modify the normal configuration of the trachea by bending sideways. Bending to the right and left results in configurations in which the trachea monotonically and smoothly bends to the first bifurcation. In the left-bent configuration, inertial particles will tend to accumulate towards the right side of the trachea and enter the right main bronchus, and conversely for the right-bent configuration. In this talk, we will present our results of Large-Eddy simulations and particle tracking showing regional deposition and ventilation as a function of the Reynolds and Stokes numbers for realistic models of the upright and bent configurations of an adult human subject. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D15.00009: Alveolar flows of the developing lungs:from embryonic to early childhood airways Janna Tenenbaum-Katan, Philipp Hofemeier, Rami Fishler, Barbara Rothen-Rutishauser, Josue Sznitman At the onset of life in utero the respiratory system is simply a liquid-filled duct. With our first breath, alveoli are filled with air and become a significant port of entry for airborne particles. As such, alveolar lining is nearly fully functional at birth, though lung development continues during childhood as structural changes increase alveolar surface area to optimize ventilation. We hypothesize that such fluid dynamical changes potentially affect two phenomena occurring within alveoli: (i) flow patterns in airspaces at distinct stages of both in- and ex-utero life and (ii) fate of inhaled particles ex-utero. To investigate these phenomena, we combine experimental and numerical approaches where (i) microfluidic in vitro devices mimic liquid flows across the epithelium of fetal airspaces, and (ii) computational simulations are employed to examine particle transport and deposition in the deep alveolated regions of infants' lungs. Our approaches capture anatomically-inspired geometries based on morphometrical data, as well as physiological flows, including the convective-diffusive nature of submicron particle transport in alveolar regions.Overall, we investigate respiratory flows in alveolar regions of developing lungs, from early embryonic stages to late childhood [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D15.00010: An automatic generation of non-uniform mesh for CFD analyses of image-based multiscale human airway models Shinjiro Miyawaki, Merryn H. Tawhai, Eric A. Hoffman, Ching-Long Lin The authors have developed a method to automatically generate non-uniform CFD mesh for image-based human airway models. The sizes of generated tetrahedral elements vary in both radial and longitudinal directions to account for boundary layer and multiscale nature of pulmonary airflow. The proposed method takes advantage of our previously developed centerline-based geometry reconstruction method. In order to generate the mesh branch by branch in parallel, we used the open-source programs Gmsh and TetGen for surface and volume meshes, respectively. Both programs can specify element sizes by means of background mesh. The size of an arbitrary element in the domain is a function of wall distance, element size on the wall, and element size at the center of airway lumen. The element sizes on the wall are computed based on local flow rate and airway diameter. The total number of elements in the non-uniform mesh (10 M) was about half of that in the uniform mesh, although the computational time for the non-uniform mesh was about twice longer (170 min). The proposed method generates CFD meshes with fine elements near the wall and smooth variation of element size in longitudinal direction, which are required, e.g., for simulations with high flow rate. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700