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 M7: Biofluids: Respiratory Flows |
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Chair: Jessica Oakes, University of Califonia at Berkeley Room: 3012 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M7.00001: Experimental investigation of particle deposition mechanisms in the lung acinus using microfluidic models. Rami Fishler, Molly Mulligan, Yael Dubowski, Josue Sznitman In order to experimentally investigate particle deposition mechanisms in the deep alveolated regions of the lungs, we have developed a novel microfluidic device mimicking breathing acinar flow conditions directly at the physiological scale. The model features an anatomically-inspired acinar geometry with five dichotomously branching airway generations lined with periodically expanding and contracting alveoli. Deposition patterns of airborne polystyrene microspheres (spanning 0.1 $\mu $m to 2 $\mu $m in diameter) inside the airway tree network compare well with CFD simulations and reveal the roles of gravity and Brownian motion on particle deposition sites. Furthermore, measured trajectories of incense particles (0.1-1 $\mu $m) inside the breathing device show a critical role for Brownian diffusion in determining the fate of inhaled sub-micron particles by enabling particles to cross from the acinar ducts into alveolar cavities, especially during the short time lag between inhalation and exhalation phases. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M7.00002: Unsteady Oxygen Transfer in Space-Filling Models of the Pulmonary Acinus Philipp Hofemeier, Lihi Shachar-Berman, Marcel Filoche, Josue Sznitman Diffusional screening in the pulmonary acinus is a well-known physical phenomenon that results from the depletion of fresh oxygen in proximal acinar generations diffusing through the alveolar wall membranes and effectively creating a gradient in the oxygen partial pressure along the acinar airways. Until present, most studies have focused on steady-state oxygen diffusion in generic sub-acinar structures and discarded convective oxygen transport due to low Peclet numbers in this region. Such studies, however, fall typically short in capturing the complex morphology of acinar airways as well as the oscillatory nature of convecive acinar breathing. Here, we revisit this problem and solve the convective-diffusive transport equations in breathing 3D acinar structures, underlining the significance of convective flows in proximal acinar generations as well as recirculating alveolar flow patterns. In particular, to assess diffusional screening, we monitor time-dependent efficiencies of the acinus under cyclic breathing motion. Our study emphasizes the necessity of capturing both a dynamically breathing and anatomically-realistic model of the sub-acinus to characterize unsteady oxygen transport across the acinar walls. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M7.00003: Turbulent dispersivity under conditions relevant to airborne disease transmission between laboratory animals Siobhan Halloran, Anthony Wexler, William Ristenpart Virologists and other researchers who test pathogens for airborne disease transmissibility often place a test animal downstream from an inoculated animal and later determine whether the test animal became infected. Despite the crucial role of the airflow in modulating the pathogen transmission, to date the infectious disease community has paid little attention to the effect of airspeed or turbulence intensity on the probability of transmission. Here we present measurements of the turbulent dispersivity under conditions relevant to experimental tests of airborne disease transmissibility between laboratory animals. We used time lapse photography to visualize the downstream transport and turbulent dispersion of smoke particulates released from a point source downstream of a standard axial fan, thus mimicking the release and transport of expiratory aerosols exhaled by an inoculated animal. We demonstrate that the fan speed counterintuitively has no effect on the downstream plume width, a result replicated with a variety of different fan types and configurations. The results point toward a useful simplification in modeling of airborne disease transmission via fan-generated flows. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M7.00004: An immersed-boundary framework for patient-specific optimization of inhaled drug delivery Laura Nicolaou, Tamer Zaki Predictive numerical simulations have the potential to significantly enhance therapies for lung disease by providing a valuable clinical aid and a platform to optimize drug delivery. A difficult challenge, however, is the influence of inter-subject variations of the airway geometries and their impact on the airflow and aerosol deposition. A personalized approach to the treatment of respiratory diseases is therefore required. An in silico framework for patient-specific predictions of the flow and aerosol deposition in the respiratory airways is presented. The approach efficiently accommodates geometric variation and airway motion in order to optimize pulmonary drug delivery. A non-rigid registration method is adopted to construct dynamic airway models conforming to the patient's breathing. Accurate predictions of the flow in realistic airway geometries are computed using direct numerical simulations (DNS) with boundary conditions enforced using a robust, implicit immersed boundary (IB) method for curvilinear meshes. A Lagrangian particle-tracking scheme is adopted to model the transport and deposition of the aerosol particles in the airways. Examples of flow and aerosol deposition in realistic extrathoracic airways and of a patient-specific dynamic lung model are presented. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M7.00005: DNS and PIV Measurements of the Flow in a Model of the Human Upper Airway Yong Wang, Liran Oren, Epharim Gutmark, Said Elghobashi The flow in the human upper airway (HUA) is 3D, unsteady, undergoes transition from laminar to turbulent, and reverses its main direction about every two seconds. In order to enhance the understanding of the flow properties, both numerical and experimental studies are needed. In the present study, DNS results of the flow in a patient-specific model of HUA are compared with experimental data. The DNS solver uses the lattice Boltzmann method which was validated [1] for some canonical laminar and turbulent flows The experimental model was constructed from transparent silicone using a mold prepared by 3D printing. Velocity measurements were performed via high speed particle image velocimetry (HSPIV). The refractive index of the fluid used in the HUA experimental model matched the refractive index of the silicone. Both inspiration and expiration cases with several flow rates in the HUA are studied. The DNS velocity fields at several cross section planes are compared with the HSPIV measurements. The computed pressure and vorticity distributions will be also presented. \\[4pt] [1] Y. Wang {\&} S. Elghobashi, (2014). Respir Physiol Neurobiol., 193, 1--10. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M7.00006: Effect of cartilaginous rings on the fluid structures in a bifurcating tube Humberto Bocanegra Evans, Luciano Castillo Fluid dynamical models of the respiratory system typically represent the bronchial tree as a collection of smooth tube bifurcations, ignoring the presence of cartilaginous rings in the first few generations, i.e. trachea and main bronchi. While accurate in certain instances, this simplification may considerably affect the results when the issue at hand is the dispersion and deposition of particles within the respiratory tract. In this study, we use a refractive index-matched particle image velocimetry facility to obtain velocity data in a scaled model of a bifurcating corrugated tube. We will present data on the fluid characteristics and how these are affected by cartilaginous rings. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M7.00007: A Missing Puzzle Piece in Murray's Law: the Optimal Angle of Junctions Ruo-Qian Wang, Katherine Taylor, Amos G. Winter Branching flows are common in biological systems, such as the circulatory and respiratory systems of animals. The optimal radii of parent and daughter branches can be explained with Murray's law, which dictates that the sum of metabolic and pumping costs is minimized. Murray's Law can be used to determine the diameter of cascading channels but misses an important parameter: the angles of the branches. Past hydraulic studies have investigated the angle effect, but have not focused on whether this geometry follows Murray's Law; while a simple network optimization is able to show that at low Reynolds numbers a branch with a parent channel connecting to $n$ equally distant channels obeying Murray's Law has a minimum total head loss with a branching angle $\theta $, such that $\cos \theta =n^{-\frac{2}{3}}$, but it's not valid for high Reynolds number flows, which may experience separation and turbulence at the branches. The present study is focused on determining the optimal branch angle that complies with Murray's Law for moderate Reynolds numbers. Computational studies using Open FOAM and experiments using 3D printed branched channels will be presented. These results will be used to quantify the effect of Reynolds number on optimal branch geometry. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M7.00008: Physical principle of airway design in human lungs Keunhwan Park, Taeho Son, Wonjung Kim, Ho-Young Kim From an engineering perspective, lungs are natural microfluidic devices that extract oxygen from air. In the bronchial tree, airways branch by dichotomy with a systematic reduction of their diameters. It is generally accepted that in conducting airways, which air passes on the way to the acinar airways from the atmosphere, the reduction ratio of diameter is closely related to the minimization of viscous dissipation. Such a principle is formulated as the Hess-Murray law. However, in acinar airways, where oxygen transfer to alveolae occurs, the diameter reduction with progressive generations is more moderate than in conducting airways. Noting that the dominant transfer mechanism in acinar airways is diffusion rather than advection, unlike conducting airways, we construct a mathematical model for oxygen transfer through a series of acinar airways. Our model allows us to predict the optimal airway reduction ratio that maximizes the oxygen transfer in a finite airway volume, thereby rationalizing the observed airway reduction ratio in acinar airways. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M7.00009: Diurnal respiration of a termite mound Hunter King, Samuel Ocko, L. Mahadevan Many species of fungus-harvesting termites build largely empty, massive mound structures which protrude from the ground above their subterranean nests. It has been long proposed that the function of these mounds is to facilitate exchange of heat, humidity, and respiratory gases; this would give the colony a controlled climate in which to raise fungus and brood. However, the specific mechanism by which the mound achieves ventilation has remained a topic of debate, as direct measurement of internal air flows has remained difficult. By directly measuring these elusive, tiny flows with a custom sensor, we find that the mound architecture of the species Odontotermes obesus takes advantage of daily oscillations in ambient temperature to drive convection and gas transport. This contradicts previous theories, which point to internal metabolic heating and external wind as driving forces. Our result, a novel example of deriving useful work from a fluctuating scalar parameter, should contribute to better understanding insect swarm construction and possible development in passive human architecture, both of which have been spurred by previous research on termites. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M7.00010: Assessment of regional effects in pulmonary aerosol delivery using Direct Numerical Simulation (DNS) Stavros Kassinos, Fotos Stylianou, Pantelis Koullapis Recent computational studies have shown that the airflow in the upper human airways is turbulent during much of the respiratory cycle. One of the features of respiratory airflow that poses a challenge to computations based on Reynolds-Averaged Navier-Stokes (RANS) closures is the laminar-turbulent-laminar transition as the flow moves from the mouth through the glottis and down to the lower conducting airways. Turbulence and unsteadiness are expected at least through the first few bifurcations of the airways. In the case of inhaled medicines, and depending on the size of the particles in the formulation, airway bifurcations are areas of preferential deposition. Here, we use Direct Numerical Simulations (DNS) to examine aerosol deposition in the case of turbulent flow through a realistic representation of the tracheal bifurcation. We examine the flow characteristics in detail, including the turbulent structures and how they affect the deposition of particles of different sizes. DNS results are compared with RANS computations. [Preview Abstract] |
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