Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session GA: Hemodynamics II |
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Chair: Kerem Pekkan, Georgia Tech Room: Hilton Chicago Waldorf |
Monday, November 21, 2005 10:34AM - 10:47AM |
GA.00001: Patient-Specific Simulations of Reactivity in Models of the Pulmonary Vasculature: A 3-D Numerical Study with Fluid-Structure Interaction Kendall Hunter, Yanhang Zhang, Craig Lanning, D. Dunbar Ivy, Robin Shandas Insight into the progression of pulmonary hypertension may be obtained from thorough study of vascular flow during reactivity testing, an invasive diagnostic procedure which can dramatically alter vascular hemodynamics. Diagnostic imaging methods, however, are limited in their ability to provide extensive data. Here we present detailed flow and wall deformation results from simulations of pulmonary arteries undergoing this procedure. Patient-specific 3-D geometric reconstructions of the first four branches of the pulmonary vasculature were obtained clinically and meshed for use with computational software. Transient simulations in normal and reactive states were obtained from four such models were completed with patient-specific velocity inlet conditions and flow impedance exit conditions. A microstructurally based orthotropic hyperelastic model that simulates pulmonary artery mechanics under normotensive and hypoxic hypertensive conditions treated wall constitutive changes due to pressure reactivity and arterial remodeling. Pressure gradients, velocity fields, arterial deformation, and complete topography of shear stress were obtained. These models provide richer detail of hemodynamics than can be obtained from current imaging techniques, and should allow maximum characterization of vascular function in the clinical situation. [Preview Abstract] |
Monday, November 21, 2005 10:47AM - 11:00AM |
GA.00002: Analysis of flow characteristics in cerebral vasculature using stereo densitometry Gustaf M{\aa}rtensson, Michael S\"{o}derman, Tommy Andersson, Drazenko Babi\c{c}, Arne Johansson In an attempt to increase the amount of information available for the clinical evaluation of cerebral malformations, an attempt has been made to accurately predict hemodynamic flow quantities from stereo densitometric data. A high-speed x-ray registration of the injection of contrast agent in a chosen vessel is mapped on to a three-dimensional reconstruction of the vasculature that has been obtained from a rotational run of the x-ray suite. Bulk flow properties of the flow may thus be calculated by registering the arrival of contrast agent fronts to consecutive positions along the axis of the vessel. The methodology was tested for both idealised laminar cases in straight pipes, as well as with considerably more challenging in vivo cases of aneurysms. A preliminary analysis of the experimental validation runs have shown that bulk flow properties were in quantitative agreement with those measured using the techniques outline above. The evaluation of the in vivo cases, which lack other in vivo measurements for comparison, yielded plausible flow characteristics. [Preview Abstract] |
Monday, November 21, 2005 11:00AM - 11:13AM |
GA.00003: The Hemodynamics of Total Cavo-Pulmonary Connection Anatomies Chang Wang, Anvar Gilmanov, Liang Ge, Fotis Sotiropoulos, Ajit Yoganathan The single ventricle is a congenital heart defect in which the right side of the heart is hypoplastic or totally absent. This anomaly results in mixing of the oxygenated and deoxygenated blood in the single ventricle, reducing the amount of oxygen transferred to the body. In U.S. two in 1000 babies are born with a single ventricle heart defect. Palliative surgical treatments are performed in stages as the child grows. The last stage is the total cavo-pulmonary connection (TCPC), which bypasses the right side of the heart and the single ventricle drives blood throughout the pulmonary and systemic circulations. We simulate the flow in two TCPC anatomies using a sharp-interface, hybrid Cartesian/Immersed Boundary approach. The computed solutions are compared with PIV in-vitro experiments and analyzed in detail to elucidate the richness of the hemodynamics in the surgically create pouch region where the inferior and superior vena cava flows collide and bifurcate into the left and right pulmonary arteries. The effect of the connection anatomy on the flow dynamics will also be discussed. [Preview Abstract] |
Monday, November 21, 2005 11:13AM - 11:26AM |
GA.00004: A Computational Study of Energy Efficiency and Pressure Losses in the Total Cavopulmonary Connection Alison Marsden, Irene Vignon-Clementel, Jeffrey Feinstein, Charles Taylor The total cavopulmonary connection (TCPC) is an operation performed to treat single ventricle congenital heart defects. The superior and inferior vena cavae are connected to the pulmonary arteries in a t-shaped junction, separating the systemic and pulmonary circulations. In this work, we hypothesize that the effects of respiration and exercise cause significant hemodynamic disturbances and energy loss. Time- dependent, 3-D blood flow simulations are performed using a custom finite element solver and patient specific geometry. Blood flow features, pressure, and energy losses are analyzed at rest and with increasing flow rates to simulate exercise conditions. Resistance boundary conditions are enforced at the pulmonary artery outlets. Energy efficiency is high at rest but drops substantially with maximal exercise. Flow vortices increase in intensity with respiration and exercise, explaining higher energy dissipation when compared to rest. Pressure drop and energy loss in the TCPC are small at rest but increase to significant levels, even at moderate exercise. We conclude that the effects of respiration and exercise should be incorporated in models to provide realistic evaluations of TCPC performance, and for future work in optimizing TCPC geometry. [Preview Abstract] |
Monday, November 21, 2005 11:26AM - 11:39AM |
GA.00005: TeraGrid Simulations of Blood Flow in Human Arterial Tree Suchuan Dong, Leopold Grinberg, Alexander Yakhot, Spencer Sherwin, George Karniadakis We employ a hybrid approach to model interactions of blood flow in different regions of human cardiovascular network: using 3D detailed fluid dynamics within sites of interest such as artery bifurcations and a reduced set of 1D equations to model waveform coupling between sites of interest. Highly scalable algorithms enable us to conduct arterial tree simulations with realistic human artery geometries on the TeraGrid, the largest computational grid in the US. We conduct coupled cross-site computations over supercomputers distributed across the continent. The algorithms and some results will be presented. [Preview Abstract] |
Monday, November 21, 2005 11:39AM - 11:52AM |
GA.00006: Pulsatile flows in pipes with finite curvature Sarah Waters, Jennifer Siggers Motivated by the study of blood flow in a curved artery, we consider fluid flow through a curved pipe of uniform curvature, $\delta$, driven by a prescribed pulsatile axial pressure gradient. The pipe has finite (as opposed to asymptotically small) curvature, and we determine the effects of both the centrifugal and Coriolis forces on the flow. The flow is parameterised by $\delta$, the Dean number $D$, the Womersley number $\alpha$, and a secondary streaming Reynolds number $R_s$. Asymptotic solutions are developed for the cases when $D\ll1$, $R_s\ll1$ and $\delta\ll1$ using regular perturbations techniques, and also when $\alpha\gg1$ using matched asymptotic expansions. For intermediate values of the governing parameters a pseudospectral code is used to obtain numerical solutions. For flows driven by a purely oscillatory pressure gradient ($D=0$) we identify three distinct classes of stable solutions corresponding to periodic symmetric, periodic asymmetric, and quasi-periodic asymmetric. The transition between solutions is dependent on the value of $\delta$, indicating that finite curved pipes exhibit a qualitatively different solution structure from curved pipes with asymptotically small curvature. We then determine the effect of a non-zero steady component of the pressure gradient ($D\neq 0$) and show that for certain parameter values, when $D$ is above a critical value the periodic asymmetric solutions regain spatial symmetry. The effects of finite curvature can lead to substantial quantitative differences in the wall shear stress distribution, and we discuss the physiological implications. [Preview Abstract] |
Monday, November 21, 2005 11:52AM - 12:05PM |
GA.00007: Fluid flow and dissipation in intersecting counter-flow pipes Kerem Pekkan, Prasad Dasi, Chang Wang, Diane deZelicourt, Fotis Sotiropoulos, Ajit Yoganathan Intersecting pipe junctions are common in industrial and biomedical flows. For the later application, standard surgical connections of vessel lumens results a ``+'' shaped topology through a side-to-side or end-to-side anastomosis. Our earlier experimental/computational studies have compared different geometries quantifying the hydrodynamic power loss through the junction where dominant coherent structures are identified. In this study we have calculated the contribution of these structures to the total energy dissipation and its spatial distribution in the connection. A large set of idealized models are studied in which the basic geometric configuration is parametrically varied (from side-to-side to end-to-side anastomosis) which quantified the strength of the secondary flows and coherent structures as a function of the geometric configuration. Steady-state, 3D, incompressible computations are performed using the commercial CFD code FIDAP with unstructured tetrahedral grids. Selected cases are compared with the in-house code results (in Cartesian and structured grids). Grid verification and experimental validation with flow-vis and PIV are presented. Identifying the dissipation hot-spots will enable a targeted inverse design of the junction by reducing the degree of optimization with a focused parameter space. [Preview Abstract] |
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