Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D16: Biofluids: Arteries |
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Chair: Michael Plesniak, The George Washington University Room: 28B |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D16.00001: Detection of multi-scale secondary flow structures using anisotropic 2D Ricker wavelets in a bent tube model for curved arteries Daniel H. Plesniak, Kartik V. Bulusu, Michael W. Plesniak Interpretation of complex flow patterns observed in this study of a model curved artery required characterization of multiple, low-circulation secondary flow structures that were observed during the late systolic deceleration and diastolic phases under physiological inflow conditions. Phase-locked, planar vorticity PIV data were acquired at various cross-sectional locations of the 180-degree bent tube model. High circulation, deformed Dean- and Lyne-type vortices were observed during early stages of deceleration, while several smaller scale, highly deformed, low-circulation vortical patterns appeared in the core and near-wall regions during late systolic deceleration and diastolic phases. Due to the multiplicity of vortical scales and shapes, anisotropic 2D Ricker wavelets were used for coherent structure detection in a continuous wavelet transform algorithm (PIVlet 1.2). Our bio-inspired study is geared towards understanding whether optimizing the shape of the wavelet kernel will enable better resolution of several low-circulation, multi-scale secondary flow morphologies and whether new insights into the dynamics of arterial secondary flow structures can accordingly be gained. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D16.00002: Perturbation-induced secondary flow structures due to fractured stents in arterial curvatures Kartik V. Bulusu, Christopher Popma, Leanne Penna, Michael W. Plesniak An in vitro experimental investigation of secondary flow structures was performed downstream of a model stent that embodied a ``Type-IV'' stent fracture, i.e. complete transverse fracture of elements and element displacement (of 3 diameters). One part of the fractured stent was located in the curved region of a test section comprised of a 180-degree bent tube, and the velocity field measured with PIV. Secondary flow morphologies downstream of the stent were identified with a continuous wavelet transform (CWT) algorithm (PIVlet 1.2) using a 2D Ricker wavelet. A comparison of wavelet transformed vorticity fields of fractured and unfractured model stents is presented under physiological inflow conditions. During systolic deceleration, a breakdown in symmetry of vortical structures occurred with the unfractured stent, but not with the fractured model stent. Potential mechanisms to explain the differences in secondary flow morphologies include redirection of vorticity from the meridional plane of the bend to the normal plane and diffusion of vorticity. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D16.00003: A regime map for secondary flow structures under physiological and multi-harmonic inflow through a bent tube model for curved arteries Shannon M. Callahan, Kirin Caldwell, Kartik V. Bulusu, Michael W. Plesniak Secondary flow structures are known to affect wall shear stress, which is closely related to atherogenesis and drug particle deposition. A regime map provides a framework to examine phase-wise variations in secondary flow structures under physiological and multi-harmonic inflow waveforms under conditions of a fixed Womersley number (4.2) and curvature ratio (1/7). Experimental PIV data were acquired at the 90-degree location in a 180-degree curved test section of a bent tube model for curved arteries using a blood analog working fluid. Coherent structure detection was performed using a continuous wavelet transform algorithm (PIVlet 1.2) and further analysis was carried out by grouping similar secondary flow structures at a fixed secondary Reynolds numbers. Phase-locked, planar vorticity fields over one period of inflow waveform revealed size, structure and strength similarities in secondary flow morphologies during the acceleration and deceleration phases. The utility of the new regime map lies in the a priori identification of pulsatile secondary flow structures, eliminating the need for exhaustive experimentation or computing, requiring only flow rate measurements that are easily acquired under clinical conditions. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D16.00004: A viscoelastic model of shear-induced blood damage Gilad Arwatz, Alexander Smits The mechanisms responsible for blood damage (hemolysis) have been studied since the mid-1960s, and it is now widely accepted that the level of shear stress and exposure time play important roles. Several models for hemolysis have been previously proposed. However, these models are purely empirical and limited to a narrow range of shear stress and exposure time and mostly, they lack any physical basis. In this study, we propose a new non-dimensional model that captures the mechanics of the red blood cells breakdown by taking into account the viscoelastic nature of their membrane. We validate our model against experimental measurements of hemolysis caused by laminar shear stress ranging from 50Pa to 500 Pa and exposure times extending from 60 s to 300 s. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D16.00005: Volumetric lattice Boltzmann simulation for blood flow in aorta arteries Debanjan Deep, Huidan (Whitney) Yu, Shawn Teague Complicated moving boundaries pose a major challenge in computational fluid dynamics for complex flows, especially in the biomechanics of both blood flow in the cardiovascular system and air flow in the respiratory system where the compliant nature of the vessels can have significant effects on the flow rate and wall shear stress. We develop a computation approach to treat arbitrarily moving boundaries using a volumetric representation of lattice Boltzmann method, which distributes fluid particles inside lattice cells. A volumetric bounce-back procedure is applied in the streaming step while momentum exchange between the fluid and moving solid boundary are accounted for in the collision sub-step. Additional boundary-induced migration is introduced to conserve fluid mass as the boundary moves across fluid cells. The volumetric LBM (VLBM) is used to simulate blood flow in both normal and dilated aorta arteries. We first compare flow structure and pressure distribution in steady state with results from Navier-Stokes based solver and good agreements are achieved. Then we focus on wall stress within the aorta for different heart pumping condition and present quantitative measurement of wall shear and normal stress. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D16.00006: Patient specific flow dynamic simulations of flow in diseased coronary artery Carlos Moreno, Kiran Bhaganagar Patient specific simulations of patients belonging to type I: protruding, type II: ascending, type III: descending, and type IV: diffuse have been performed to understand the effect of inlet forcing frequency and amplitude on the wall shear stress (WSS). Numerical simulations are performed with unsteady flow conditions in a laminar regime. The results have revealed that at low amplitudes, the sensitivity of WSS to forcing frequency is strongly dependent on the patient type for same degree of stenosis. For all the types, the maximum WSS is observed in post-stenotic or the distal region of the stenosis, and WSS has lowest magnitude at the peak location of the stenosis. For higher pulsatile amplitude (a $>$ 1.0), WSS exhibits a strong sensitivity with forcing frequencies for all types. However, at higher forcing frequency the WSS exhibits nonlinear response to the inlet forcing frequency, which is strongly type dependent. The study clearly demonstrated differences between the intra-type flows are small compared to the inter-type flows. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D16.00007: Numerical Investigation of Heat Transfer and Flow Characteristics of non-Newtonian Blood Flow in Atherosclerosis Coronary Artery: the Effect of Magnetic Field Siavash Ghaffari, Shima Alizadeh, Mohammad Sadeq Karimi Temperature heterogeneity in plaque containing inflammatory cells can cause thermal stress, and accelerates rupture process. Activated inflammatory cells embedded in plaques release heat while the plaque is cooled by blood flow. In the present work, arterial wall temperature distribution of atherosclerotic Right Coronary in the presence of external uniform and multi-directional magnetic field is investigated by numerical methods. The rheology of the flowing blood is modeled by a generalized Power law model. An advanced coupled FEM-FVM algorithm is used to determine temperature distribution inside the artery. Transient Navier-Stokes and energy equations in 2D idealized arterial model of a bending artery coupled with Maxwell's equations are discretized using the Finite-Volume Method and solved by SIMPLE algorithm in curvilinear coordinate to analyze pulsatile blood flow, whereas the transient heat conduction equation in the plaque is solved simultaneously with these equations using Finite-Element Method. The plaque temperature, Nusselt Number and heat flux at the plaque/lumen interface is obtained for different states of magnetic field and different Power law indices (n) to investigate influence of produced electromagnetic force and blood viscosity on the cooling effect of blood. It is observed that how magnetic field and blood dilution modifies the temperature heterogeneity of plaque and decreases probability of rupture of Atherosclerotic plaque. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D16.00008: Wall Shear Stress in Aorta with Coarctation and Post-Stenotic Dilatation - Scale Resolved Simulation of Pulsatile Blood Flow Roland Gardhagen, Matts Karlsson Large eddy simulations of pulsating blood flow in an idealized model of a human aorta with a coarctation and a post-stenotic dilatation were conducted before and after treatment of the stenosis using Ansys Fluent. The aim was to study wall shear stress (WSS), which influences the function of endothelial cells, and turbulence, which may play a role in thrombus formation. Phase average values of WSS before the treatment revealed high shear in the stenosis at peak systole, as expected, but also at the end of the dilatation. In the dilatation backflow causes a negative peak. Diastolic WSS is characterized by low amplitude oscillations, which promotes atherogenesis. Also noticeable is the asymmetric pattern between the inner and outer sides of the vessel caused by the arch upstream of the stenosis. Thus, large spatial, temporal, and probably asymmetric WSS gradients in the already diseased region suggest increased risk for further endothelial dysfunction. This reflects a complex, partly turbulent, flow pattern that may disturb the blood flow in the abdominal aorta. After treatment of the stenosis, but not the dilatation, fluctuations of velocity and WSS were still found, thus harmful flow conditions still exist. [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D16.00009: Blood flow characteristics in the aortic arch Lisa Prahl Wittberg, Stevin van Wyk, Mihai Mihaiescu, Laszlo Fuchs, Ephraim Gutmark, Philippe Backeljauw, Iris Gutmark-Little The purpose with this study is to investigate the flow characteristics of blood in the aortic arch. Cardiovascular diseases are associated with specific locations in the arterial tree. Considering atherogenesis, it is claimed that the Wall Shear Stress (WSS) along with its temporal and spatial gradients play an important role in the development of the disease. The WSS is determined by the local flow characteristics, that in turn depends on the geometry as well as the rheological properties of blood. In this numerical work, the time dependent fluid flow during the entire cardiac cycle is fully resolved. The Quemada model is applied to account for the non-Newtonian properties of blood, an empirical model valid for different Red Blood Cell loading. Data obtained through Cardiac Magnetic Resonance Imaging have been used in order to reconstruct geometries of the the aortic arch. Here, three different geometries are studied out of which two display malformations that can be found in patients having the genetic disorder Turner's syndrome. The simulations show a highly complex flow with regions of secondary flow that is enhanced for the diseased aortas. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D16.00010: Fluid-structure interaction analysis on the effect of vessel wall hypertrophy and stiffness on the blood flow in carotid artery bifurcation Sang Hoon Lee, Hyoung Gwon Choi, Jung Yul Yoo The effect of artery wall hypertrophy and stiffness on the flow field is investigated using three-dimensional finite element method for simulating the blood flow. To avoid the complexity due to the necessity of additional mechanical constraints, we use the combined formulation which includes both the fluid and structural equations of motion into single coupled variational equation. A P2P1 Galerkin finite element method is used to solve the Navier-Stokes equations for fluid flow and arbitrary Lagrangian-Eulerian formulation is used to achieve mesh movement. The Newmark method is employed for solving the dynamic equilibrium equations for linear elastic solid mechanics. The pulsatile, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed with Womersley velocity profile at the inlet and constant pressure at the outlet. The study shows that the stiffness of carotid artery wall affects significantly the flow phenomena during the pulse cycle. Similarly, it is found that the flow field is also strongly influenced by wall hypertrophy. [Preview Abstract] |
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