Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L18: Biofluids: Respiratory and Aerosols |
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Chair: Alison Marsden, University of California, San Diego Room: 28D |
Monday, November 19, 2012 3:35PM - 3:48PM |
L18.00001: Geometrical influence of pulmonary acinar models on respiratory flows and particle deposition Philipp Hofemeier, Josue Sznitman Due to experimental challenges in assessing respiratory flows in the deep regions of the lungs, computational simulations are typically sought to quantify inhaled aerosol transport and deposition in the acinus. Most commonly, simulations are performed using generic geometries of alveoli, including spheres, toroids and polyhedra to mimic the acinar region. However, local respiratory flows and ensuing particle trajectories are anticipated to be highly influenced by the specific geometrical structures chosen. To date, geometrical influences have not yet been thoroughly quantified. Knowing beforehand how geometries affect acinar flows and particle transport is critical in translating simulated data to predictions of aerosol deposition in real lungs. Here, we conduct a systematic investigation on a number of generic acinar models. Simulations are conducted for simple alveolated airways featuring a selection of geometries. Deposition patterns and efficiencies are quantified both for massless particles, highlighting details of the local flow, and micron-scale aerosols. This latter group of particles represents an important class of inhaled aerosols known to reach and deposit in the acinus. Our work emphasizes the subtleties of acinar geometry in determining the fate of inhaled aerosols. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L18.00002: Direct Numerical Simulation of the Flow in the Human Upper Airway Yong Wang, Said Elghobashi The objective of our study is to understand the flow details in the critical zones inside the human upper airway (HUA) to minimize the guess work in performing surgeries for removing flow obstructions. The 3D flow in HUA consists of unsteady laminar, transitional and turbulent regimes. We perform DNS of HUA flow using lattice Boltzmann method (LBM). We validated our DNS- LBM via comparisons with other DNS methods and experiments for several canonical flows. Excellent agreement was achieved for 3D turbulent channel flow of Kim et al. (JFM 1987) and experimental data for 3D flows in curved pipes. Our predictions of the flow in an idealized HUA model agree well with the experimental data. We predict the flow in a real HUA whose geometry is reconstructed from optical coherence tomography (OCT) data. Both inspiration and expiration cases with various inflow rates are studied. Velocity, pressure and shear stress distributions, time-dependent trajectories of tracer particles and instantaneous streamlines throughout the domain are presented. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L18.00003: Numerical investigation of pulmonary drug delivery under mechanical ventilation conditions Arindam Banerjee, Timothy Van Rhein The effects of mechanical ventilation waveform on fluid flow and particle deposition were studied in a computer model of the human airways. The frequency with which aerosolized drugs are delivered to mechanically ventilated patients demonstrates the importance of understanding the effects of ventilation parameters. This study focuses specifically on the effects of mechanical ventilation waveforms using a computer model of the airways of patient undergoing mechanical ventilation treatment from the endotracheal tube to generation G7. Waveforms were modeled as those commonly used by commercial mechanical ventilators. Turbulence was modeled with LES. User defined particle force models were used to model the drag force with the Cunningham correction factor, the Saffman lift force, and Brownian motion force. The endotracheal tube (ETT) was found to be an important geometric feature, causing a fluid jet towards the right main bronchus, increased turbulence, and a recirculation zone in the right main bronchus. In addition to the enhanced deposition seen at the carinas of the airway bifurcations, enhanced deposition was also seen in the right main bronchus due to impaction and turbulent dispersion resulting from the fluid structures created by the ETT. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L18.00004: Effect of Pressure Controlled Waveforms on Flow Transport and Gas mixing in a Patient Specific Lung Model during Invasive High Frequency Oscillatory Ventilation Mohammed Alzahrany, Arindam Banerjee A computational fluid dynamic study is carried out to investigate gas transport in patient specific human lung models (based on CT scans) during high frequency oscillatory ventilation (HFOV). Different pressure-controlled waveforms and various ventilator frequencies are studied to understand the effect of flow transport and gas mixing during these processes. Three different pressure waveforms are created by solving the equation of motion subjected to constant lung wall compliance and flow resistance. Sinusoidal, exponential and constant waveforms shapes are considered with three different frequencies 6, 10 and 15 Hz and constant tidal volume 50 ml. The velocities are calculated from the obtained flow rate and imposed as inlet flow conditions to represent the mechanical ventilation waveforms. An endotracheal tube ETT is joined to the model to account for the effect of the invasive management device with the peak Reynolds number (Re) for all the cases ranging from 6960 to 24694. All simulations are performed using high order LES turbulent model. The gas transport near the flow reversal will be discussed at different cycle phases for all the cases and a comparison of the secondary flow structures between different cases will be presented. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L18.00005: A Comprehensive Breath Plume Model for Disease Transmission via Expiratory Aerosols S.K. Halloran, A.S. Wexler, W.D. Ristenpart The peak in influenza incidence during wintertime represents a longstanding unresolved scientific question. One hypothesis is that the efficacy of airborne transmission via aerosols is increased at low humidity and temperature, conditions that prevail in wintertime. Recent experiments with guinea pigs suggest that transmission is indeed maximized at low humidity and temperature, a finding which has been widely interpreted in terms of airborne influenza virus survivability. This interpretation, however, neglects the effect of the airflow on the transmission probability. Here we provide a comprehensive model for assessing the probability of disease transmission via expiratory aerosols between test animals in laboratory conditions. The spread of aerosols emitted from an infected animal is modeled using dispersion theory for a homogeneous turbulent airflow. The concentration and size distribution of the evaporating droplets in the resulting ``Gaussian breath plume'' are calculated as functions of downstream position. We demonstrate that the breath plume model is broadly consistent with the guinea pig experiments, without invoking airborne virus survivability. Moreover, the results highlight the need for careful characterization of the airflow in airborne transmission experiments. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L18.00006: Correlation among regional ventilation, airway resistance and particle deposition in normal and severe asthmatic lungs Sanghun Choi, Eric A. Hoffman, Merryn H. Tawhai, Ching-Long Lin Computational fluid dynamic simulations are performed to investigate flow characteristics and quantify particle deposition with normal and severe asthmatic lungs. Continuity and Navier-Stokes equations are solved with unstructured meshes and finite element method; a large eddy simulation model is adopted to capture turbulent and/or transitional flows created in the glottis. The human airway models are reconstructed from CT volumetric images, and the subject-specific boundary condition is imposed to the 3D ending branches with the aid of an image registration technique. As a result, several constricted airways are captured in CT images of severe asthmatic subjects, causing significant pressure drop with high air speed because the constriction of airways creates high flow resistance. The simulated instantaneous velocity fields obtained are then employed to track transport and deposition of 2.5 $\mu $m particles. It is found that high flow resistance regions are correlated with high particle-deposition regions. In other words, the constricted airways can induce high airway resistance and subsequently increase particle deposition in the regions. This result may be applied to understand the characteristics of deposition of pharmaceutical aerosols or bacteria. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L18.00007: Numerical simulation of non-equilibrium transient flow during inhalation Olaf Marxen, Thierry Magin The flow in human upper airways may be laminar, transitional, or turbulent. Breadth-by-breadth and patient-specific variability is expected to have a significant influence on laminar-turbulent transition. The flow path of therapeutic drug aerosols may be strongly affected by the transition-induced unsteady structures. The unsteady Navier-Stokes equations are solved numerically to simulate the flow through a channel-flow geometry representative of an airway segment. In order to trigger transition, small-amplitude disturbances are forced via wall blowing/suction. We perform multiple simulations with varying phase of the forced disturbances. Ensemble averaging then allows to compute mean and RMS values. A time-dependent channel center-line velocity serves to model the change in flow velocity during inhalation. The uncertainty associated with variability during breathing is quantified using non-intrusive stochastic collocation. Simulation results reveal that we have intervals in time and space with quasi-steady equilibrium and with strong non-equilibrium flow. The uncertainty associated with the breathing pattern may strongly affect the occurrence of laminar-turbulent transition, leading to large uncertainties when RMS values are peaking. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L18.00008: Multiscale Airflow Model and Aerosol Deposition in Healthy and Emphysematous Rat Lungs Jessica Oakes, Alison Marsden, Celine Grandmont, Chantal Darquenne, Irene Vignon-Clementel The fate of aerosol particles in healthy and emphysematic lungs is needed to determine the toxic or therapeutic effects of inhalable particles. In this study we used a multiscale numerical model that couples a 0D resistance and capacitance model to 3D airways generated from MR images. Airflow simulations were performed using an in-house 3D finite element solver (SimVascular, simtk.org). Seven simulations were performed; 1 healthy, 1 uniform emphysema and 5 different cases of heterogeneous emphysema. In the heterogeneous emphysema cases the disease was confined to a single lobe. As a post processing step, 1 micron diameter particles were tracked in the flow field using Lagrangian particle tracking. The simulation results showed that the inhaled flow distribution was equal for the healthy and uniform emphysema cases. However, in the heterogeneous emphysema cases the delivery of inhaled air was larger in the diseased lobe. Additionally, there was an increase in delivery of aerosol particles to the diseased lobe. This suggests that as the therapeutic particles would reach the diseased areas of the lung, while toxic particles would increasingly harm the lung. The 3D-0D model described here is the first of its kind to be used to study healthy and emphysematic lungs. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L18.00009: Measurement of ciliary flow generated on the surface of tracheal lumen Koki Kiyota, Hironori Ueno, Takuji Ishikawa, Keiko Numayama-Tsuruta, Yohsuke Imai, Toshihiro Omori, Takami Yamaguchi Although we consistently take air with virus and bacteria, these harmful substances are trapped on the surface of tracheal lumen and transported toward larynx from the trachea and bronchi by effective ciliary motion and swallowed it (clearance function). However, the 3-dimensional flow field generated by inhomogeneously distributed ciliary cells are largely unknown. In this study, we first succeeded to measure the ciliated cells' density by staining actin of the epithelial cells and tubulin of the cilia, respectively. Second, we analyzed the ciliary motion by labeling the tip of cilia with fluorescent particles, and tracking their movements to understand the mechanism of the flow generation. Last, in order to clarify the flow field induced by the ciliary motion, we measured the motion of tracer particles on the surface of tracheal epithelial cells by a confocal micro-PTV system. The results show that the mean velocity and the velocity disturbance decayed rapidly as the height from the epithelial cells were increased. [Preview Abstract] |
Monday, November 19, 2012 5:32PM - 5:45PM |
L18.00010: Particle Image Velocimetry Measurements in Anatomically-Accurate Models of the Mammalian Nasal Cavity C. Rumple, J. Richter, B.A. Craven, M. Krane A summary of the research being carried out by our multidisciplinary team to better understand the form and function of the nose in different mammalian species that include humans, carnivores, ungulates, rodents, and marine animals will be presented. The mammalian nose houses a convoluted airway labyrinth, where two hallmark features of mammals occur, endothermy and olfaction. Because of the complexity of the nasal cavity, the anatomy and function of these upper airways remain poorly understood in most mammals. However, recent advances in high-resolution medical imaging, computational modeling, and experimental flow measurement techniques are now permitting the study of airflow and respiratory and olfactory transport phenomena in anatomically-accurate reconstructions of the nasal cavity. Here, we focus on efforts to manufacture transparent, anatomically-accurate models for stereo particle image velocimetry (SPIV) measurements of nasal airflow. Challenges in the design and manufacture of index-matched anatomical models are addressed and preliminary SPIV measurements are presented. Such measurements will constitute a validation database for concurrent computational fluid dynamics (CFD) simulations of mammalian respiration and olfaction. [Preview Abstract] |
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