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 BD: Biofluids I |
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Chair: Rajat Mital, George Washington University Room: Salt Palace Convention Center 151 A-C |
Sunday, November 18, 2007 10:34AM - 10:47AM |
BD.00001: In vivo measurement of blood flow in the vitelline network Christian Poelma, Peter Vennemann, Ralph Lindken, Jerry Westerweel The growth and adaptation of blood vessels is studied $in$ $vivo$ in the so-called vitelline network of a chick embryo. The vitelline network, a system of extra-embryonic blood vessels that transports nutrients from the yolk sac to the chick embryo, is an easily accessible model system for the study of human cardiovascular development and functioning. We present measurements obtained by means of scanning microscopic Particle Image Velocimetry. Using phase-locking, we can reconstruct the full three-dimensional flow as a function of the cardiac cycle. Typical reconstructed volumes are 0.4$\times$0.5$\times$0.2 mm$^3$ with a spatial resolution (i.e. vector spacing) of 6 $\mu m$. These hemodynamic measurements allow a study of the coupling between form and functioning of the blood vessels. Special attention is given to the local wall shear stress (WSS), an important physiological parameter that is thought to determine - to great extent - the adaptation of the vessels to changing conditions. The WSS can be estimated directly from the velocity gradient at the wall or from a fit to the blood velocity profile. The former method slightly underestimates the WSS (most likely due to lack of resolution) but is significantly easier to apply in the complex geometries under consideration. [Preview Abstract] |
Sunday, November 18, 2007 10:47AM - 11:00AM |
BD.00002: Investigation of Unsteady Secondary Flow Structures in a Curved Tube using MRI Velocimetry Sean Peterson, Chekema Prince, Vinay Pai, Joshly Varghese, Michael Plesniak Under certain conditions, pulsatile flow in a curved tube can exhibit secondary flow patterns which are remarkably different from the steady flow Dean's vortices at an equivalent mean Reynolds number. For instance at sufficiently high Womersley number ($\sim $15), viscous effects are limited to thin Stokes' layers, in which counter-rotating vortical structures are established. These structures induce a counter-rotating vortex pair within the core of the tube with a sense of rotation opposite to that of the steady flow Dean's vortices. In the present study, the axial and secondary flow development in a curved tube subjected to harmonic (sinusoidal) and physiologically-inspired pulsatile waveforms (representative of the cardiovascular circulation in the carotid artery) are investigated using Magnetic Resonance Imaging velocimetry over a range of Reynolds and Womersley numbers. The results are compared to measurements by more traditional experimental techniques such as PIV and LDV. The implications of disturbances introduced into the Stokes' layer, e.g. the structural members of stents, on the global secondary flow structure are discussed. [Preview Abstract] |
Sunday, November 18, 2007 11:00AM - 11:13AM |
BD.00003: Measurement of Velocity Profiles of in Vitro Blood Flow Using Micro Particle Image Velocimetry. F.J. Diez, M.M. Torregrosa, J. Torres, S. Pothos In vitro blood flow in microchannels was studied using micro-particle image Velocimetry (microPIV). Experimental measurements of blood flow in microvessels with internal diameter 10-1000 $\mu $m is a major challenge in biofluids. This is due to the fact that blood flow is composed of many constituents that behave as multiphase suspensions. MicroPIV measurements were taken in different microchannel configurations including straight square channels, T-channels, converging channels and an L channel for three fluid types: (1) de-ionized water as our based fluid, (2) with hematocrit ratio of 10{\%}, and (3) hematocrit ratio of 20{\%}. The hematocrit ratio (HR) is defined as the ratio of the volume of packed red cells to the total blood volume. 2D mean velocity profiles of blood flow at various depths in microchannels were obtained. In order to get the spatial distributions of these mean velocities, 100 instantaneous velocity fields were obtained, and ensemble-averaged for each condition. Typical two-dimensional Poiseuille flow with a parabolic velocity profile for the de-ionized water flow was observed while the profiles became blunter and could not be easily approximated by Poiseuille parabolic solution as we increased the hematocrit ratio. [Preview Abstract] |
Sunday, November 18, 2007 11:13AM - 11:26AM |
BD.00004: Shock formation and nonlinear dispersion in a microvascular network Oliver Jensen, Rares Pop, Sarah Waters, Giles Richardson Temporal and spatial fluctuations in capillary blood flow are a common feature of microvascular networks. Among many possible causes of instability, previous authors have suggested that the nonlinear rheological properties of capillary blood flow (notably the Farhaeus effect, the Farhaeus-Lindqvist effect and the phase separation effect at bifurcations) may be sufficient to generate temporal fluctuations even in very simple networks. We have simulated blood flow driven by a fixed pressure drop through a simple arcade network using coupled hyperbolic PDEs that incorporate empirical descriptions of these rheological effects; we solved these PDEs using a characteristic-based method. Our computations indicate that, under physiological conditions, there is a unique steady solution in an arcade network which is linearly stable and that plasma skimming suppresses the oscillatory decay of perturbations. In addition, we find that nonlinear perturbations to this flow develop shocks via the Farhaeus effect, providing a novel mechanism for nonlinear dispersion in microvascular networks. [Preview Abstract] |
Sunday, November 18, 2007 11:26AM - 11:39AM |
BD.00005: Womersley analysis for arbitrarily unsteady flow in elastic vessels G. Brereton, J. Slade, R. Meyer In the 1950's, Womersley developed a theoretical analysis of flow in elastic-walled vessels that is continuous and periodically unsteady. In this talk, we describe a similar analysis of flows that can have arbitrary non-periodic unsteadiness and are at some instant stationary, as are found in some of the smaller arteries. The resulting analytical flow relationships are compared with MRI measurements of flow-rate and of local-velocity time histories in the popliteal arteries of patients. They are found to be in good agreement over conditions that both precede and follow acute patient exercise. [Preview Abstract] |
Sunday, November 18, 2007 11:39AM - 11:52AM |
BD.00006: The numerical study of the deformed behavior of vesicles in a shear flow. Xiaobo Gong, Shu Takagi, Yoichiro Matsumoto Two types of vesicles, the liposome and red blood cell are modeled with the immersed boundary method. The lipid bilayer membrane model is adopted for the liposome, in which the Helfrich's (1973) bending energy model and the surface tension with tolerable dilation of surface area are used; the hyper-elastic model is used for the red blood cell, in which Hookean model for bending stress and Skalak's (1973) model for hyper-elastic in plane stress are adopted. The numerical result suggests that, because the hyper-elastic membrane of a red blood cell is ``stiffer'' than the lipid bilayer membrane of a liposome, the viscosity ratio between inside and outside the vesicle that the tumbling motion is observed is smaller for a red blood cell than for a liposome. The interactions of multiple liposome and red blood cells in the rectangular channel flow are presented and discussed. [Preview Abstract] |
Sunday, November 18, 2007 11:52AM - 12:05PM |
BD.00007: Computational framework for understanding flow in large vessels Shawn Shadden, Andrea Les, Charles Taylor It is widely accepted that hemodynamic flow structures, such as separation or recirculation, play an important role in the progression of vascular diseases and vascular remodeling. However understanding these flow structures and how they accompany biologic response is far from being well understood. Medical imaging can allow a qualitative understanding of the flow through large vessels, but obtaining quantitative information or parametric analysis inevitably requires computational models. We will present computations from patient- specific and idealized vascular models. These computations reveal complicated, three-dimensional flow structures. Previous simulations have often been under-resolved and the flow structures have not been sufficiently characterized. We will describe some of our progress on resolving these flow patterns, especially in regions susceptible to disease. [Preview Abstract] |
Sunday, November 18, 2007 12:05PM - 12:18PM |
BD.00008: Hemodynamics of Curved Vessels with Stenosis Michael E. Boghosian, Kevin W. Cassel In hemodialysis access, the brachiocephalic or upper-arm fistula has less than optimal functional rates. The cause of this reduced patency is stenosis due to intimal hyperplasia in the cephalic vein. Stenosis typically leads to thrombosis and ultimately failure of the fistula. To increase our understanding of this process, numerical simulations of the unsteady, two-dimensional, incompressible Navier-Stokes equations are solved for the flow in an infinite channel having curvature and stenosis. Physiologically relevant Reynolds numbers ranging from 300 to 1500 and stenosis percentages of 0, 25, 50, and 75 are modeled. The post-stenotic flow is characterized by strong shear layers and recirculation regions. The largest shear stresses are found just upstream of the stenosis apex. The maximum shear stress increases with increasing Reynolds number and percent stenosis. The results indicate that hemodynamic conditions in the vein after fistula creation combined with curvature of the cephalic arch lead to shear stresses that exceed normal physiological values (both minimum and maximum). In some cases, the shear stresses are sufficiently large to cause damage to the endothelium and possibly denudation. [Preview Abstract] |
Sunday, November 18, 2007 12:18PM - 12:31PM |
BD.00009: Direct Numerical Simulations of Whole Blood Robert MacMeccan, Jonathan Clausen, Paul Neitzel, Cyrus Aidun Hundreds of three-dimensional, deformable red blood cells and platelets are simulated at physiologic hematocrit using the recently developed lattice-Boltzmann--finite-element method. This method provides the efficiency and versatility to simulate large suspensions while accurately modeling biconcave red blood cells as elastic membranes with bending stiffness and an internal solution of hemoglobin. Bulk rheology of whole blood at continuum-level scales is quantitatively described with effective viscosity and shear-thinning behavior. Suspension microstructure and red-blood-cell deformation compares well with experimental measures. The local stress environment that platelets experience in whole blood is described as it pertains to shear-mediated platelet adhesion with 25{\%} of platelets experiencing a surface shear stress greater than twice the effective suspension stress. [Preview Abstract] |
Sunday, November 18, 2007 12:31PM - 12:44PM |
BD.00010: Experimental results of harmonically oscillating flexible and rigid flat plates. Jeremy Pena, Scott Hightower, James Allen, Paulo Ferreira de Sousa, Banavara Shashikanth The thrust produced by high aspect ratio oscillating flexible and rigid flat plates are measured using Particle Image Velocimetry over a range of Strouhal numbers in a the large water channel facility at New Mexico State University. Power input to the system was also measured. Results show that neutral/zero thrust is produced at a Strouhal number of 0.14 for all the plates. The thrust co-efficient for the stiff plates are superior to the flexible ones, however the efficiency of the flexible plates is order twice that of the stiff plates. The reason for this is that the flexible plate are resonating with the fluid. [Preview Abstract] |
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