Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G16: Biofluids: Physiological V - Respiratory System Flows |
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Chair: Brent A. Craven, Pennsylvania State University Room: 304 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G16.00001: On locating the obstruction in the human upper airway Yong Wang, S. Elghobashi The fluid dynamical properties of the air flow in the human upper airway (UA) are not fully understood at present due to the three-dimensional, patient-specific complex geometry of the airway, flow transition from laminar to turbulent and flow-structure interaction during the breathing cycle. One of the major challenges to surgeons is determining the location of the UA obstruction before performing corrective surgeries. It is quite difficult at present to experimentally measure the instantaneous velocity and pressure at specific points in the human airway. On the other hand, direct numerical simulation (DNS) can predict all the flow properties and resolve all its relevant length- and time-scales. We developed a DNS solver with lattice Boltzmann method (LBM), and used it to investigate the flow in two patient-specific UAs reconstructed from CT scan data. Inspiration and expiration flows through these two airways are studied and compared. Pressure gradient-time signals at different locations in the UAs are used to determine the location of the obstruction. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G16.00002: A fully resolved fluid-structure-muscle-activation model for esophageal transport Wenjun Kou, Amneet P.S. Bhalla, Boyce E. Griffith, Mark Johnson, Neelesh A. Patankar Esophageal transport is a mechanical and physiological process that transfers the ingested food bolus from the pharynx to the stomach through a multi-layered esophageal tube. The process involves interactions between the bolus, esophageal wall composed of mucosal, circular muscle (CM) and longitudinal muscle (LM) layers, and neurally coordinated muscle activation including CM contraction and LM shortening. In this work, we present a 3D fully-resolved model of esophageal transport based on the immersed boundary method. The model describes the bolus as a Newtonian fluid, the esophageal wall as a multi-layered elastic tube represented by springs and beams, and the muscle activation as a traveling wave of sequential actuation/relaxation of muscle fibers, represented by springs with dynamic rest lengths. Results on intraluminal pressure profile and bolus shape will be shown, which are qualitatively consistent with experimental observations. Effects of activating CM contraction only, LM shortening only or both, for the bolus transport, are studied. A comparison among them can help to identify the role of each type of muscle activation. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G16.00003: Effect of Time-dependent Pressure Boundary Condition on Flow Transport in a Patient Specific Lung Model during Invasive High Frequency Oscillatory Ventilation Mohammed Alzahrany, Arindam Banerjee Large eddy simulation was used to investigate gas transport in a human lung (image-based) model during high frequency oscillatory ventilation (HFOV). A time-dependent pressure boundary condition as a function of the flow rate and coupled resistance-compliance was imposed at the outlets. The study was conducted for three different HFOV frequencies of 6, 10 and 15 Hz; a constant tidal volume of 50 ml and various compliance ratios (1, 4 and 10). The results are compared to computations that use traditional boundary conditions (such as pre-specified flow and constant pressure), experimental and gamma scintgraphy results. While traditional pre-specified mass fraction boundary condition failed to capture the Pendelluft flow at regional lung units that are observed in experiments, our modified resistance-compliance based pressure boundary condition was successful in predicting this feature. The impact of compliance ratio and frequency on phase-delay at different lung sections and its effect on secondary flow and turbulence will also be presented. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G16.00004: Effect of morphological variability on particle deposition in idealized human airways Eleanor Lin, Jorge A. Bernate, Daniel A. Parada San Martin, Yuzo Makitani, Eric S. G. Shaqfeh, Gianluca Iaccarino This study is focused on the effects of variability in airway morphology on particle deposition in the lungs, which in turn impacts disease inception and drug delivery. We generated a parameterized geometry of the human airway derived from Lola: a realistic geometry obtained from CT scans (Zhang et. al J AEROSOL SCI 46, 34 (2012)). The upper airway geometry is parameterized using an elliptic model from Xi and Longest (ANN BIOMED ENG 35,560 (2007)), with the glottis modified to a realistic triangular shape, based on measurements taken from Lola. The trachea and bronchi are generated using rules adapted from Kitaoka et. al. (J Appl Physiol 87, 2207-2217 (1999)), with the first 3 generations closely matching those of Lola. We perform simulations corresponding to a full breathing cycle and illustrate the preferential deposition in each generation. In addition, we compared the deposition features in the idealized geometry to those from simulations in the original scanned airways. Perturbations are then applied to the parameterized geometry to study the effects of morphological variability on deposition patterns. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G16.00005: Renal hemodynamics: the influence of the renal artery ostium flow diverter Jenn Stroud Rossmann, Scott Albert, Robert Balaban The recently identified renal artery ostium flow diverter may preferentially direct blood flow to the renal arteries, and may also influence flow patterns and recirculation known to be involved in atherogenesis. Three-dimensional computational fluid dynamics (CFD) simulations of steady and pulsatile blood flow are performed to investigate the influence of diverter size and position, and vascular geometry, on the flow patterns and fluid mechanical forces in the neighborhood of the diverter. CFD results show that the flow diverter does affect the blood distribution: depending on the diverter's position, the flow to the renal arteries may be increased or reduced. The results of simulations also show the diverter's effect on the Wall Shear Stress (WSS) distribution, and suggest that the diverter contributes to an atherogenic environment in the abdominal aorta, while being atheroprotective in the renal arteries themselves. These results support previous clinical findings, and suggest directions for further clinical study. The results of this work have direct implications in understanding the physiological significance of the diverter, and its potential role in the pathophysiological development of atherosclerosis. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G16.00006: Simulation of the flow field and particle deposition in a realistic geometry of the human airways Jorge A. Bernate, Eleanor Lin, Eric S.G. Shaqfeh, Gianluca Iaccarino Using the dynamic Smagorinsky sub-grid scale model, we carry out Large Eddie Simulations (LES) of the flow field in a realistic geometry reconstructed from a CT scan of an adult male human subject (Zhang et. al J AEROSOL SCI 46, 34 (2012)). The geometry comprises the oral cavity, larynx, trachea, and bronchi extending to generations 6 to 9. The computed time-averaged flow field is validated with magnetic resonance velocimetry (MRV) measurements obtained in a 3D printed model of the realistic geometry (Andrew J. Banko, Filippo Coletti, Daniele Schiavazzi, Christopher J. Elkins, John K. Eaton, submitted to this conference). The comparison is done at a constant inspiratory flow rate of 60 L/min, at which turbulence is expected to develop. Probing the mean flow, we compare integral factors quantifying the ventilation, the shape of stream-wise velocity profile, and the strength of secondary flows in different branches. Via simulations, we also characterize the unsteadiness of the flow, focusing on the dynamics of the laryngeal jet and its effect on the structure of the flow field and particle deposition patterns. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G16.00007: An image-based automatic mesh generation and numerical simulation for a population-based analysis of aerosol delivery in the human lungs Shinjiro Miyawaki, Merryn H. Tawhai, Eric A. Hoffman, Ching-Long Lin The authors propose a method to automatically generate three-dimensional subject-specific airway geometries and meshes for computational fluid dynamics (CFD) studies of aerosol delivery in the human lungs. The proposed method automatically expands computed tomography (CT)-based airway skeleton to generate the centerline (CL)-based model, and then fits it to the CT-segmented geometry to generate the hybrid CL-CT-based model. To produce a turbulent laryngeal jet known to affect aerosol transport, we developed a physiologically-consistent laryngeal model that can be attached to the trachea of the above models. We used Gmsh to automatically generate the mesh for the above models. To assess the quality of the models, we compared the regional aerosol distributions in a human lung predicted by the hybrid model and the manually generated CT-based model. The aerosol distribution predicted by the hybrid model was consistent with the prediction by the CT-based model. We applied the hybrid model to 8 healthy and 16 severe asthmatic subjects, and average geometric error was 3.8{\%} of the branch radius. The proposed method can be potentially applied to the branch-by-branch analyses of a large population of healthy and diseased lungs. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G16.00008: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 9:44AM - 9:57AM |
G16.00009: A Comparative Study of Airflow and Odorant Deposition in the Mammalian Nasal Cavity Joseph Richter, Christopher Rumple, Allison Ranslow, Andrew Quigley, Benison Pang, Thomas Neuberger, Michael Krane, Blaire Van Valkenburgh, Brent Craven The complex structure of the mammalian nasal cavity provides a tortuous airflow path and a large surface area for respiratory air conditioning, filtering of inspired contaminants, and olfaction. Due to the small and contorted structure of the nasal turbinals, nasal anatomy and function remains poorly understood in most mammals. Here, we utilize high-resolution MRI scans to reconstruct anatomically-accurate models of the mammalian nasal cavity. These data are used to compare the form and function of the mammalian nose. High-fidelity computational fluid dynamics (CFD) simulations of nasal airflow and odorant deposition are presented and used to compare olfactory function across species (primate, rodent, canine, feline, ungulate). [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G16.00010: Convective-diffusive particle transport in pulmonary acinar models Philipp Hofemeier, Josue Sznitman Much of our understanding of the transport and deposition of fine inhaled particles ($\leq1~\mu$m) in the deep regions of the lungs results from numerical simulations that revolve around the central assumption that fine aerosols are mainly influenced by local convective airflows. Recently, it has been noted that aerosol transport in the pulmonary acinus relies however on the complex coupling between convective, diffusive processes, as captured by the appropriate dimensionless particle numbers (Sznitman, {\it J. Biomech.}, 2013). It is anticipated that for particles in the range of 0.5~--~1~$\mu$m, the coupling of intrinsic particle motion with acinar flow fields ultimately governs deposition outcomes. In an effort to address the influence of convective-diffusive mechanisms on aerosol transport and deposition, we present a detailed investigation of fine particle transport in the absence and presence of stochastic Brownian motion. Further, we study systematically the effects of particle properties (e.g., diameter) as well as acinar lung generation on the ensemble statistics of inhaled fine particles and their deposition. Our findings reveal the intimate coupling between local acinar flow structures and intrinsic particle motion leading to complex irreversible aerosol kinematics. [Preview Abstract] |
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