Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session FF: Biofluids VI |
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Chair: Don Webster, Georgia Institute of Technology Room: Salt Palace Convention Center 151 G |
Monday, November 19, 2007 8:00AM - 8:13AM |
FF.00001: Mixing and Transport in the Small Intestine: A Lattice-Boltzmann Model Gino Banco, James Brasseur, Yanxing Wang, Amit Aliani, Andrew Webb The two primary functions of the small intestine are absorption of nutrients into the blood stream and transport of material along the gut for eventual evacuation. The primary transport mechanism is peristalsis. The time scales for absorption, however, rely on mixing and transport of molecules between the bulk flow and epithelial surface. Two basic motions contribute to mixing: peristalsis and repetitive segmental contraction of short segments of the gut. In this study we evaluate the relative roles of peristalsis vs. segmental contraction on the degree of mixing and time scales of nutrient transport to the epithelium using a two-dimensional model of flow and mixing in the small intestine. The model uses the lattice-Boltzmann framework with second-order moving boundary conditions and passive scalar (Sc = 10). Segmental and peristaltic contractions were parameterized using magnetic resonance imaging data from rat models. The Reynolds numbers (1.9), segment lengths (33 mm), max radii (2.75 mm) and occlusion ratios (0.33) were matched for direct comparison. Mixing is quantified by the rate of dispersion of scalar from an initial concentration in the center of the segment. We find that radial mixing is more rapid with segmental than peristaltic motion, that radial dispersion is much more rapid than axial, and that axial is comparable between the motions. [Preview Abstract] |
Monday, November 19, 2007 8:13AM - 8:26AM |
FF.00002: A Multiscale Lattice-Boltzmann Model of Macro-to-Micro Scale Transport Relevant to Gut Function Yanxing Wang, James Brasseur, Gino Banco Nutrient and pharmaceutical absorption in the small intestine involve coupled multiscale transport and mixing processes that span several orders of magnitude. We hypothesize that muscle-induced villi motions generate and control a ``micro-mixing layer'' that couples with macro-scale mixing to enhance molecular transport to and from the epithelium. In this work we developed a 2-D numerical method based on a multigrid strategy within the lattice-Boltzmann framework. We model a macro-scale cavity flow with microscale finger-like villi in pendular motion on the lower surface and evaluate the coupling between macro and micro-scale fluid motions, scalar mixing, and uptake of passive scalar at the villi surface. Preliminary results show that the moving villi can be effective mixers at the micro scale, especially when groups of villi move in a coordinated, but out-of-phase fashion. A time-evolving series of flow recirculation eddies are generated within a micro mixing layer that increase transport of passive scalar from the macro eddy to the surface by advection. Flow parameters such as frequency of pendular motion, spacing between villi and villi grouping, have strong influences on the behaviors of the micro-mixing layer and the efficiency of scalar transport. An extensive analysis is in process to quantify correlation between scalar mixing and flux, details of villi motion, and induced flow patterns. [Preview Abstract] |
Monday, November 19, 2007 8:26AM - 8:39AM |
FF.00003: Direct visualization of internal respiratory and food transport dynamics in insects Wah-Keat Lee, John Socha, Mark Westneat, Jon Harrison, James Waters Although the internal physiological dynamics of large species, especially humans, are well understood, this is not true for small millimeter-sized animals such as insects. Because of their size and in general, optically opaque exteriors, direct visualization of internal insect physiology has not been possible. As such, biologists have relied on indirect techniques, such as gas exchange or pressure measurements, coupled with histology/dissection, and external observations to infer internal dynamics. A new technique, x-ray phase-contrast imaging, have, for the first time, allowed direct visualization of the internal dynamics related to insect physiology. Compression of air sacs and trachea, and the uptake and transport of food in insects have been seen for the first time. These measurements have raised many questions and call for further theoretical research into these complex systems. [Preview Abstract] |
Monday, November 19, 2007 8:39AM - 8:52AM |
FF.00004: A Overset Grid Method for Fourth Order Evolution Equations of Human Tear Film K.L. Maki, R.J. Braun, T.A. Driscoll, A. Heryudono, P.E. King-Smith, P. Fast We developed an overset grid method to simulate the formation and relaxation of the human tear film over multiple blink cycles. We studied limiting cases of the absence and presence of insoluble surfactants on the film's free surface. The evolution is described by a single fourth order nonlinear partial differential equation that arises from lubrication theory on a domain whose length varies significantly with time. Numerical computations, found by implementing a finite difference based method of lines on a overset grid, explore the dynamics of the tear film including the effects of evaporation, gravity, intermolecular forces and reflex tearing. Comparison with in vivo measurements are made. [Preview Abstract] |
Monday, November 19, 2007 8:52AM - 9:05AM |
FF.00005: Single-Equation Models for the Tear Film in a Blink Cycle with Realistic Lid Motion A. Heryudono, R.J. Braun, T.A. Driscoll, K.L. Maki, L.P. Cook, P.E. King-Smith We model the tear film using two limits of the strength of the Marangoni effect for an insoluble surfactant: either it is completely ineffectual (stress free case) or very strong (uniform stretching limit). A single nonlinear partial differential equation (PDE) arises in either case from lubrication theory that governs film thickness over multiple blink cycles. Slip on the film bottom, viscosity and surface tension and a time-varying domain that mimics realistic movement of the upper eyelid are included. Dirichlet and third order boundary conditions are applied. The realistic lid motion, together with new choices for flux functions at the end ends and the ability to apply them, extends prior sinusoidal results. Numerical experiments indicate that a spectral collocation method based on the method of lines together with a backward differentiation-style ODE solver is more accurate and more efficient than our prior uniform grid finite-difference method. Numerical computations also yield results that agree in many respects with in vivo observations of the tear film under partial blink conditions. Partial blinks are shown to be effectively equivalent to a full blink by looking for periodic solutions as a function of closure fraction. [Preview Abstract] |
Monday, November 19, 2007 9:05AM - 9:18AM |
FF.00006: Groovy flow patterns in the fish ear Charlotte W. Kotas, Peter H. Rogers, Minami Yoda The dense, bony otoliths contained in the fish ear oscillate with respect to their surrounding tissue and endolymph in the presence of sound waves. How an otolith actually transduces this acoustically induced fluid motion into the hair cell displacements that the fish ``hears'' is not fully understood, however. The fluid flow created by the oscillation of the irregularly shaped otolith has both steady and unsteady components. Since most of the hair cells are next to a grooved area on the otolith, the sulcus, the otolith was modeled as a grooved spheroid oscillating in a quiescent Newtonian fluid. Particle-image velocimetry and pathline visualizations for the steady streaming flows within the groove are presented for oscillation at 0\r{ }--90\r{ } with respect to the body axis of symmetry $Re=2\pi f\,L^2/\nu =O(10-10^2)$, and $\varepsilon =s/L\approx 0.025-0.05$. Here, $\nu $ is the fluid kinematic viscosity, $L$ is a typical length based on the spheroid, and $f$ and $s$ are the oscillation frequency and amplitude, respectively. Results for bodies oscillated by multiple frequencies $f_{1}$ and $f_{2}$ along the same direction imply that the velocity fields are the superposition of those due to the component frequencies for small values of $\varepsilon $. [Preview Abstract] |
Monday, November 19, 2007 9:18AM - 9:31AM |
FF.00007: Quantifying the 3D Odorant Concentration Field Used by Actively Tracking Blue Crabs D.R. Webster, B.D. Dickman, J.L. Jackson, M.J. Weissburg Blue crabs and other aquatic organisms locate food and mates by tracking turbulent odorant plumes. The odorant concentration fluctuates unpredictably due to turbulent transport, and many characteristics of the fluctuation pattern have been hypothesized as useful cues for orienting to the odorant source. To make a direct linkage between tracking behavior and the odorant concentration signal, we developed a measurement system based the laser induced fluorescence technique to quantify the instantaneous 3D concentration field surrounding actively tracking blue crabs. The data suggest a correlation between upstream walking speed and the concentration of the odorant signal arriving at the antennule chemosensors, which are located near the mouth region. More specifically, we note an increase in upstream walking speed when high concentration bursts arrive at the antennules location. We also test hypotheses regarding the ability of blue crabs to steer relative to the plume centerline based on the signal contrast between the chemosensors located on their leg appendages. These chemosensors are located much closer to the substrate compared to the antennules and are separated by the width of the blue crab. In this case, it appears that blue crabs use the bilateral signal comparison to track along the edge of the plume. [Preview Abstract] |
Monday, November 19, 2007 9:31AM - 9:44AM |
FF.00008: The anatomy and internal aerodynamics of canine olfaction Brent Craven, Eric Paterson, Gary Settles High-resolution magnetic resonance imaging (MRI) scans of the nasal airway of a large dog reveal an intricate scrollwork of nasal conchae providing large surface area for heat, moisture, and odorant transfer. From these anatomical scans we reconstruct a 3-D surface model of the nasal passage and extract detailed morphometric data providing insight into the internal airflows of canine olfaction. A complicated airway network is revealed, wherein the branched maxilloturbinate and ethmoturbinate scrolls are structurally distinct. 3-D airway connectivity also reveals separate respiratory and olfactory flow paths. Knowing the approximate airflow rate and frequency of canine sniffing, we find Reynolds numbers that are, surprisingly, well below the turbulent-flow threshold. Finally, the internal aerodynamics and transport phenomena of canine olfaction are considered via non-dimensional analysis and initially-simple theoretical and computational models. (To appear in the Anatomical Record.) [Preview Abstract] |
Monday, November 19, 2007 9:44AM - 9:57AM |
FF.00009: Exposure assessment involving entrainment during human motion in the indoor environment David Marr, Ian Spitzer, Mark Glauser Recent experimental studies have shown the effects of motion on the human thermal plume (Settles). When utilizing low speed ventilation designs, this natural convection is a primary driving force of the flow. Interference with this flow reduces the effectiveness of a displacement design and therein reduces air quality and comfort levels in the indoor environment. Human motion has been found to increase mixing in a room (Mora and Gadgil) with displacement ventilation, a negative effect due to the nature of the design. This investigation is the culmination of PDA and PIV measurements around a thermal manikin and the direct impact seated human rotation has on air velocity, particle concentration and size associated with the thermal plume. This common indoor motion in a cubicle setting may assist in exposure studies and ventilation design to determine the effectiveness of displacement style ventilation in a near realistic setting. [Preview Abstract] |
Monday, November 19, 2007 9:57AM - 10:10AM |
FF.00010: Experiments on Dust Levitation due to Foot Motion Hiroshi Higuchi, Yoshihiro Kubota Near wall aerodynamics and dust levitation process from the floor due to human foot stomping and walking were investigated. Actual human foot kinematics was first recorded, and input to the laboratory experiment. At present, the foot movement was limited in the vertical direction without any ankle articulation. To focus on the aerodynamic effect on dust suspension and avoid the floor vibration, the model was stopped immediately before contacting the floor. Sole geometries ranged from a disk, an elongated flat plate to an indoor slipper. The suspended particle pattern showed the zone from which particles were suspended effectively. With the elongated plate and the shoe shape, strong directionality in particle suspension was shown associated with a concentrated area of vertical structure. Lateral streaks on the particle pattern were considered to be caused by vortex instabilities. The upward foot motion was also found to be effective in dust levitation from the floor. The time-dependent velocity field was measured with a PIV, and the particle concentration measurement with image analysis was conducted. Basic fluid dynamics as well as its practical implications will be addressed. [Preview Abstract] |
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