Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session G25: Biofluids: Respiratory Flows |
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Chair: Alexandra Techet, MIT Room: 304 |
Monday, November 23, 2015 8:00AM - 8:13AM |
G25.00001: 3D Spray Droplet Distributions in Sneezes Alexandra Techet, Barry Scharfman, Lydia Bourouiba 3D spray droplet clouds generated during human sneezing are investigated using the Synthetic Aperture Feature Extraction (SAFE) method, which relies on light field imaging (LFI) and synthetic aperture (SA) refocusing computational photographic techniques. An array of nine high-speed cameras are used to image sneeze droplets and tracked the droplets in 3D space and time (3D + T). An additional high-speed camera is utilized to track the motion of the head during sneezing. In the SAFE method, the raw images recorded by each camera in the array are preprocessed and binarized, simplifying post processing after image refocusing and enabling the extraction of feature sizes and positions in 3D + T. These binary images are refocused using either additive or multiplicative methods, combined with thresholding. Sneeze droplet centroids, radii, distributions and trajectories are determined and compared with existing data. The reconstructed 3D droplet centroids and radii enable a more complete understanding of the physical extent and fluid dynamics of sneeze ejecta. These measurements are important for understanding the infectious disease transmission potential of sneezes in various indoor environments. [Preview Abstract] |
Monday, November 23, 2015 8:13AM - 8:26AM |
G25.00002: A computational model that simulates mucociliary clearance in the bronchial tree, and a concomitant study on energetics and optimality Michail Manolidis, Daniel Isabey, Bruno Louis, James Grotberg, Marcel Filoche Systemic deterministic models of mucociliary clearance in the bronchial tree are currently scarce. While analytical/computational efforts have focused on microscopic modeling of mucociliary propulsion, macroscopic approaches have been restricted mainly to stochastic methods. We present an analytical/computational model that simulates mucociliary clearance in macroscopic physical domains. The analytical foundations of the model are based on a Stokes flow assumption, whereby, in addition to viscous forces originating in ciliary forcing, the role of surface tension is also considered. The governing equations are solved computationally on a three-dimensional surface mesh. Flow is simulated in an anatomically/geometrically representative bifurcation of the bronchial tree. The directionality of ciliary forcing in our model is optimized in order to maintain near-uniform mucus film thickness throughout the flow field. Based on the optimized version of the model, energetic considerations, as well as aspects of optimality in nature are analyzed and presented. [Preview Abstract] |
Monday, November 23, 2015 8:26AM - 8:39AM |
G25.00003: Effect of kinematics and flexibility on the pumping dynamics of an array of oscillating plates Farhad Saffaraval, Ken Kiger A robotic array of two-dimensional oscillating plates was constructed to examine the net pumping produced over a transition from viscous to inertia dominated flows. The actuators consist of single rigid plates or multiple rigid segments connected with a thin polymer film to provide for a specified degree of flexibility. The parameters for the study include: 1) inter-gill phase difference, 2) asymmetry of the protraction/retraction stroke speeds, and 3) the presence of a one-way elastic hinge. PIV measurements were conducted to examine the unsteady two-dimensional flow field at a sufficient resolution to provide measurements of the net pumped flow rate, energy dissipation, and pumping efficiency. Preliminary results at a Reynolds number of 15 show that the introduction of asymmetric flexibility under synchronous actuation of a sinusoidal waveform provides an increasing flow rate with increased flexibility. Introduction of an asymmetric stroke kinematics, however, appears to nullify the improvement effect of flexibility, with rigid and flexible gills providing comparable levels of pumping performance when using the same stroke pattern. Using a combination of stroke phasing and asymmetric kinematics shows further enhancement beyond the use of either individually. [Preview Abstract] |
Monday, November 23, 2015 8:39AM - 8:52AM |
G25.00004: Investigation of mucus transport in an idealized lung airway model using multiphase CFD analysis Rahul Rajendran, Arindam Banerjee Mucus, a Bingham fluid is transported in the pulmonary airways by consistent beating of the cilia and exhibits a wide range of physical properties in response to the core air flow and various pathological conditions. A better understanding of the interfacial instability is required as it plays a crucial role in gas transport, mixing, mucus clearance and drug delivery. In the current study, mucus is modelled as a Newtonian fluid and the two phase gas-liquid flow in the airways is investigated using an inhomogeneous Eulerian-Eulerian approach. The complex interface between the phases is tracked using the conventional VOF (Volume of Fluid) method. Results from our CFD simulations which are performed in idealized single and double bifurcation geometries will be presented and the influence of airflow rate, mucus layer thickness, mucus viscosity, airway geometry (branching {\&} diameter) and surface tension on mucus flow behavior will be discussed. Mean mucus layer thickness, pressure drop due to momentum transfer {\&} increased airway resistance, mucus transport speed and the flow morphology will be compared to existing experimental and theoretical data. [Preview Abstract] |
Monday, November 23, 2015 8:52AM - 9:05AM |
G25.00005: A Computational Approach for Capturing Topological Changes during the Splitting of Liquid Plug by a Pulmonary Bifurcation Benjamin Vaughan, James Grotberg There are certain medical treatments that involve the introduction of exogenous liquids in the lungs. These liquids can form plugs within the airways that may then propagate throughout the branching network of the lungs. The propagation through the pulmonary branches can cause the liquid plugs to split. The understanding this splitting process is important for effective administration of various treatments such as surfactant replacement therapy. A significant complication in modeling the splitting process is the possibility of a topological change where the two air fingers defining the leading and trailing meniscus split into a topologically distinct configuration that consists of two liquid plugs bounded by three air fingers (one trailing and two leading). To study this process, we introduce a two-dimensional computational model that captures the propagation and splitting of a liquid plug along with the topological changes. This model consists of a finite element solver coupled with a narrow band level set approach for tracking the air/liquid interface and is shown to be efficient in capturing the full splitting process and allows for the estimation of the ratio of the resulting plugs to each other after the original plug has been split. [Preview Abstract] |
Monday, November 23, 2015 9:05AM - 9:18AM |
G25.00006: Role of Topological Heterogeneity on the Fate of Inhaled Aerosols in the Pulmonary Acinus Philipp Hofemeier, Kenichiro Koshiyama, Shigeo Wada, Josue Sznitman Particle transport, and ultimately deposition outcomes, in the acinar region of the lungs are intrinsically coupled with local the shape and morphology of the airways and alveolar cavities (Hofemeier and Sznitman, 2015). Thus, it is paramount to capture the complexity and heterogeneity of the acinar environment in order to predict realistic aerosol dynamics. Recently, Koshiyama and Wada (2015) introduced an algorithm to generate acinar models with space-filling heterogeneous alveolar structures to mimic realistic in vivo environments. Their model is able to reproduce the characteristic polyhedral shape and size of alveolar cavities as well as the length and branching angles of the connecting airways. Here, we utilize for the first time such acinar models as the basis for numerical simulations of respiratory acinar flows and particle transport. By generating and modeling various heterogeneous multi-generation acinar models, we aim to shed light on the role of spatial acinar heterogeneity on particle deposition fate, as a function of inhaled particle size and breathing maneuvers. The present studies are a first step towards predicting realistic acinar deposition patterns indicative for whole lung statistics as well as inter-acinar differences. [Preview Abstract] |
Monday, November 23, 2015 9:18AM - 9:31AM |
G25.00007: Experimental evolution of sprays in a lung model Javier Burguete, Alberto Aliseda We present the first results of an experiment conceived to observe the evolution of sprays inside the lungs. We have built a model that covers the first 6 generations (from the trachea to segmental bronchi of 5th generation). This setup is placed on a wind tunnel, and the flow inside the model is induced by a vacuum pump that emulates the breathing process using a valve. We inject a previously determined distribution of particles (water droplets), whose average diameter can be modified. Then, we measure the droplet distribution in different branches and compare how the droplet distribution is modified at each generation. The parameters that control the behavior are the average diameter of the original distribution, the airflow rate inside the model and the frequency of the breathing cycle. [Preview Abstract] |
Monday, November 23, 2015 9:31AM - 9:44AM |
G25.00008: 3D Model of Surfactant Replacement Therapy. James Grotberg, Cheng-Feng Tai, Marcel Filoche Surfactant Replacement Therapy (SRT) involves instillation of a liquid-surfactant mixture directly into the lung airway tree. Though successful in neonatal applications, its use in adults had early success followed by failure. We present the first mathematical model of 3D SRT where a liquid plug propagates through the tree from forced inspiration. In two separate modeling steps, the plug first deposits a coating film on the airway wall which subtracts from its volume, a ``coating cost''. Then the plug splits unevenly at the airway bifurcation due to gravity. The steps are repeated until a plug ruptures or reaches the tree endpoint alveoli/acinus. The model generates 3D images of the resulting acinar distribution and calculates two global indexes, efficiency and homogeneity. Simulating published literature, the earlier successful adult SRT studies show comparatively good index values, while the later failed studies do not. Those unsuccessful studies used smaller dose volumes with higher concentration mixtures, apparently assuming a well mixed compartment. The model shows that adult lungs are not well mixed in SRT due to the coating cost and gravity effects. Returning to the higher dose volume protocols could save many thousands of lives annually in the US. [Preview Abstract] |
Monday, November 23, 2015 9:44AM - 9:57AM |
G25.00009: Aerosol transport and deposition efficiency in the respiratory airways Laura Nicolaou, Tamer Zaki Prediction of aerosol deposition in the respiratory system is important for improving the efficiency of inhaled drug delivery and for assessing the toxicity of airborne pollutants. Particle deposition in the airways is typically described as a function of the Stokes number based on a reference flow timescale. This choice leads to significant scatter in deposition data since the velocity and length scales experienced by the particles as they are advected through the flow deviate considerably from the reference values in many sections of the airways. Therefore, the use of an instantaneous Stokes number based on the local properties of the flow field is proposed instead. We define the effective Stokes number as the time-average of the instantaneous value. Our results demonstrate that this average, or effective, Stokes number can deviate significantly from the reference value particularly in the intermediate Stokes number range. In addition, the effective Stokes number shows a very clear correlation with deposition efficiency, and is therefore a more appropriate parameter to describe aerosol transport. [Preview Abstract] |
Monday, November 23, 2015 9:57AM - 10:10AM |
G25.00010: Respiratory flows during early childhood: Computational models to examine therapeutic aerosols in the developing airways. Janna Tenenbaum-Katan, Philipp Hofemeier, Josué Sznitman Inhalation therapy is the cornerstone of early-childhood respiratory treatments, as well as a rising potential for systemic drug delivery and pulmonary vaccination. As such, indispensable understanding of respiratory flow phenomena, coupled with particle transport at the deep regions of children's lungs is necessary to attain efficient targeting of aerosol therapy. However, fundamental research of pulmonary transport is overwhelmingly focused on adults. In our study, we have developed an anatomically-inspired computational model of representing pulmonary acinar regions at several age points during a child's development. Our numerical simulations examine respiratory flows and particle deposition maps within the acinar model, accounting for varying age dependant anatomical considerations and ventilation patterns. Resulting deposition maps of aerosols alter with age, such findings might suggest that medication protocols of inhalation therapy in young children should be considered to be accordingly amended with the child's development. Additionally to understanding basic scientific concepts of age effects on aerosol deposition, our research can potentially contribute practical guidelines to therapy protocols, and its' necessary modifications with age. [Preview Abstract] |
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