Physiological Flow Studies in Exact-Replica Atherosclerotic Carotid Bifurcations

2003 ◽  
Author(s):  
J. Bale-Glickman ◽  
K. Selby ◽  
D. Saloner ◽  
O¨. Savas¸
Keyword(s):  
Chaotic Behavior ◽  
Three Dimensional ◽  
Carotid Bifurcation ◽  
Flow Patterns ◽  
Shear Stresses ◽  
Multiple Sources ◽  
Complex Flow ◽  
Physiological Flow ◽  
Image Velocimetry ◽  
Recirculation Zones

Some results from a series of physiological flow experiments in a model of an atherosclerotic carotid bifurcation are presented. The flow model exactly replicates the lumen of the plaque excised intact from a patient with severe carotid atherosclerosis. Flow visualization (FV) and particle image velocimetry (PIV) are employed as the tools for this study. The complex internal geometry of the diseased artery combined with the pulsatile input flows gives rise to complex flow patterns. The flow fields are highly three-dimensional and chaotic with details varying from cycle to cycle. These flow patterns also include internal jets, three-dimensional shear layers, numerous separation/recirculation zones and stagnation lines. The vorticity and streamline maps confirm this complex and three-dimensional nature of the flow. Planar streamline maps show the three-dimensional flow by the multiple sources/sinks throughout the model. Wall shear stresses (WSS) are estimated to range form about −7 Pa to 34 Pa at the stenotic neck over time with the peak at peak systolic. These WSS also exhibit chaotic behavior during pulsatile flow cycles.

Experimental Flow Studies in Exact-Replica Phantoms of Atherosclerotic Carotid Bifurcations Under Steady Input Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 38-48 ◽  
Author(s):  
J. Bale-Glickman ◽  
K. Selby ◽  
D. Saloner ◽  
O¨. Savas¸
Keyword(s):  
Three Dimensional ◽  
Carotid Bifurcation ◽  
Reynolds Numbers ◽  
Flow Fields ◽  
Shear Stresses ◽  
Treatment Technique ◽  
Input Flow ◽  
Stagnation Points ◽  
Topological Features ◽  
Recirculation Zones

Extensive flow studies are conducted in two carotid bifurcation flow phantoms. These phantoms exactly replicate the lumen of the plaque excised intact from two patients with severe carotid atherosclerosis. The input flow into the phantom’s common carotid artery is steady. Novel scanning techniques for flow visualization and particle image velocimetry are used. In addition, a novel boundary treatment technique is employed in velocimetry to extract first order accurate velocity gradients at walls. The data show that the flow fields are highly three-dimensional. Numerous separation and recirculation zones dominate the flow domain, except at the lowest Reynolds numbers. The separation regions are often so severe that highly directed internal jets form. At high Reynolds numbers, the flows become unsteady and chaotic, even though the input flow is steady. Flow fields have large regions of energetic flow and almost stagnant recirculation zones. These recirculation zones range in size from the full size of the arteries to zones within crevasses smaller than 1 mm. Velocity field and streamline patterns conform well to the lumen geometry. The streamlines are highly tortuous. Stagnation points correlate well with the topological features of the stenosis. Vorticity maps confirm the highly complex and three dimensional nature of the flow. Wall shear stresses at the stenoses are estimated to be on the order of 10 Pa. These studies conclusively show that the nature of the flow in the diseased bifurcation is primarily dictated by the lumen geometry.

scholarly journals Computational Fluid Dynamics (CFD) as a Tool for Investigating Self-Organized Ascending Bubble-Driven Flow Patterns in Champagne Glasses

Foods ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 972
Author(s):  
Fabien Beaumont ◽  
Gérard Liger-Belair ◽  
Guillaume Polidori
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Bubble Column ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Complex Flow ◽  
Self Organized ◽  
Laser Tomography ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd

Champagne glasses are subjected to complex ascending bubble-driven flow patterns, which are believed to enhance the release of volatile organic compounds in the headspace above the glasses. Based on the Eulerian–Lagrangian approach, computational fluid dynamics (CFD) was used in order to examine how a column of ascending bubbles nucleated at the bottom of a classical champagne glass can drive self-organized flow patterns in the champagne bulk and at the air/champagne interface. Firstly, results from two-dimensional (2D) axisymmetric simulations were compared with a set of experimental data conducted through particle image velocimetry (PIV). Secondly, a three-dimensional (3D) model was developed by using the conventional volume-of-fluid (VOF) multiphase method to resolve the interface between the mixture’s phases (wine–air). In complete accordance with several experimental observations conducted through laser tomography and PIV techniques, CFD revealed a very complex flow composed of surface eddies interacting with a toroidal flow that develops around the ascending bubble column.

Characteristics of 3D Turbulent Wall Jets and Offset Jets With Small Offset Ratios

2009 ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Three Dimensional ◽  
Symmetry Plane ◽  
Shear Stresses ◽  
Wall Jets ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
Turbulent Wall Jets ◽  
The Mean ◽  
Turbulent Wall ◽  
Proper Orthogonal

This paper reports an experimental study of turbulent three-dimensional generic wall jets and offset jets. The jets were created from a long circular pipe. A particle image velocimetry technique was used to conduct velocity measurements in the symmetry plane of the jet. From these measurements, the salient features of the flows are reported in terms of the mean velocities, turbulence intensities and Reynolds shear stresses. The energy spectra and profiles of reconstructed turbulence intensities and Reynolds shear stresses from low order proper orthogonal decomposition modes are also reported.

Targeted Particle Tracking in Computational Models of Human Carotid Bifurcations

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Ian Marshall
Keyword(s):  
Healthy Volunteer ◽  
Carotid Artery ◽  
Flow Region ◽  
Carotid Bifurcation ◽  
Flow Patterns ◽  
External Carotid ◽  
Complex Flow ◽  
Imaging Science ◽  
Carotid Bulb ◽  
Human Carotid

A significant and largely unsolved problem of computational fluid dynamics (CFD) simulation of flow in anatomically relevant geometries is that very few calculated pathlines pass through regions of complex flow. This in turn limits the ability of CFD-based simulations of imaging techniques (such as MRI) to correctly predict in vivo performance. In this work, I present two methods designed to overcome this filling problem, firstly, by releasing additional particles from areas of the flow inlet that lead directly to the complex flow region (“preferential seeding”) and, secondly, by tracking particles both “downstream” and “upstream” from seed points within the complex flow region itself. I use the human carotid bifurcation as an example of complex blood flow that is of great clinical interest. Both idealized and healthy volunteer geometries are investigated. With uniform seeding in the inlet plane (in the common carotid artery (CCA)) of an idealized bifurcation geometry, approximately half the particles passed through the internal carotid artery (ICA) and half through the external carotid artery. However, of those particles entering the ICA, only 16% passed directly through the carotid bulb region. Preferential seeding from selected regions of the CCA was able to increase this figure to 47%. In the second method, seeding of particles within the carotid bulb region itself led to a very high proportion (97%) of pathlines running from CCA to ICA. Seeding of particles in the bulb plane of three healthy volunteer carotid bifurcation geometries led to much better filling of the bulb regions than by particles seeded at the inlet alone. In all cases, visualization of the origin and behavior of recirculating particles led to useful insights into the complex flow patterns. Both seeding methods produced significant improvements in filling the carotid bulb region with particle tracks compared with uniform seeding at the inlet and led to an improved understanding of the complex flow patterns. The methods described may be combined and are generally applicable to CFD studies of fluid and gas flow and are, therefore, of relevance in hemodynamics, respiratory mechanics, and medical imaging science.

scholarly journals Flow instabilities in a graft anastomosis: A study of the instantaneous velocity fields

2001 ◽  
Vol 215 (6) ◽  
pp. 579-587 ◽  
Author(s):  
C J Bates ◽  
D M O'Doherty ◽  
D Williams
Keyword(s):  
Intimal Hyperplasia ◽  
Bypass Graft ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Instantaneous Velocity ◽  
Working Fluid ◽  
Shear Stresses ◽  
Complex Flow ◽  
Image Velocimetry ◽  
Arterial Bypass Graft

The major cause of arterial bypass graft failure is intimal hyperplasia. Fluctuating wall shear stresses in the graft, which are associated with disturbed flow, are believed to be important factors in the development and localization of intimal hyperplasia. This study, based upon water as the working fluid, has investigated the flow structure inside a 30° Y-junction with different fillet radii at the intersection between the graft and the host artery at various Reynolds numbers and distal outlet segment (DOS) to proximal outlet segment (POS) flow ratios. The structure of the flow has been investigated experimentally using particle image velocimetry (PIV). The two-dimensional instantaneous velocity fields confirm the existence of a very complex flow, especially in the toe and heel regions for the different fillet radii and clearly identify features such as sinks, sources, vortices and strong time dependency.

Conceptual Design of an Adaptive Wind Tunnel for the Generation of Unsteady Complex Flow Patterns

2005 ◽  
Author(s):  
Richard Kirkman ◽  
Meredith Metzger
Keyword(s):  
Wind Tunnel ◽  
Virtual Environments ◽  
Conceptual Design ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Mesh Size ◽  
Flow Patterns ◽  
Complex Flow ◽  
Tunnel Design ◽  
Wind Tunnel Design

The present paper describes the conceptual design of a three-dimensional adaptive wind tunnel capable of generating complex, unsteady flow fields in a relatively compact physical domain. The design involves multiple, independently controllable vents located around the periphery of a semi-enclosed facility. Desired flow patterns at target areas within the facility are produced by actively steering the inlet flow via appropriately adjusting the magnitude and direction of the air flow entering from each vent. The present study is motivated by a desire to incorporate tactile wind sensation into CAVE-like virtual environments, thereby increasing the overall sense of immersion in the virtual reality. The present wind tunnel design concept may also have potential application to laboratory studies of such problems as unsteady aerodynamics. Results in the present study include examples of two flow patterns obtained from numerical simulations using Fluent. Results from a companion parametric study analyzing the sensitivity of the numerical solution to mesh size and tolerance are also provided. In addition, the feasibility of using a linear-based control strategy to generate prescribed flow patterns within the wind tunnel is discussed.

Experimental Investigation on the Thermal and Flow Characteristics in the IRWST Under Spraying of the Steam From Automatic Depressurization System in AP1000 Plant

2016 ◽  
Author(s):  
Daogang Lu ◽  
Yuhao Zhang ◽  
Zhongyi Wang ◽  
Guanghao Wu ◽  
Qiong Cao
Keyword(s):  
Thermal Stratification ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Convection Flow ◽  
Water Storage Tank ◽  
Image Velocimetry ◽  
Large Tank ◽  
Coolant System

In AP1000 plant, the automatic depressurization system (ADS) works to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the In-containment Refueling Water Storage Tank (IRWST) in the LOCA conditions. In particular, for the AP1000 plant, both the IRWST and ADS spargers are specially designed, and the ADS spargers are located in one corner of the IRWST. All the factors lead to the special and complicated thermal and flow behavior in the IRWST, which in turn have great influences on the condensation effects of the ejected steam. In the present work, an overall scaled-down IRWST and ADS sparger models are built to study the condensation and mixing phenomena in the accidental depressurization events in AP1000. Thermocouples matrix with more than 200 T-type sheathed thermocouples are utilized to measure the three dimensional temperature in the large tank. The Particle Image Velocimetry (PIV) is employed for the measurement of the natural convection flow velocity. Based on the experimental data, the local spraying flow patterns, flow behavior, and thermal stratification phenomena in IRWST etc. are analyzed. The results indicate that the spraying steam condensation flow patterns are closely related to the subcooling degree in the IRWST. In addition, the stratification number is developed to evaluate the thermal stratification extent in the IRWST, which indicates that only part of the fluid are used efficiently for condensing the spraying steam directly.

scholarly journals Flow patterns in three-dimensional porcine epicardial coronary arterial tree

2007 ◽  
Vol 293 (5) ◽  
pp. H2959-H2970 ◽  
Author(s):  
Yunlong Huo ◽  
Thomas Wischgoll ◽  
Ghassan S. Kassab
Keyword(s):  
Scaling Laws ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Diameter Ratio ◽  
Complex Flow ◽  
Arterial Tree ◽  
Main Trunk ◽  
Flow Divider ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

The branching pattern of epicardial coronary arteries is clearly three-dimensional, with correspondingly complex flow patterns. The objective of the present study was to perform a detailed hemodynamic analysis using a three-dimensional finite element method in a left anterior descending (LAD) epicardial arterial tree, including main trunk and primary branches, based on computed tomography scans. The inlet LAD flow velocity was measured in an anesthetized pig, and the outlet pressure boundary condition was estimated based on scaling laws. The spatial and temporal wall shear stress (WSS), gradient of WSS (WSSG), and oscillatory shear index (OSI) were calculated and used to identify regions of flow disturbances in the vicinity of primary bifurcations. We found that low WSS and high OSI coincide with disturbed flows (stagnated, secondary, and reversed flows) opposite to the flow divider and lateral to the junction orifice of the main trunk and primary branches. High time-averaged WSSG occurs in regions of bifurcations, with the flow divider having maximum values. Low WSS and high OSI were found to be related through a power law relationship. Furthermore, zones of low time-averaged WSS and high OSI amplified for larger diameter ratio and high inlet flow rate. Hence, different focal atherosclerotic-prone regions may be explained by different physical mechanism associated with certain critical levels of low WSS, high OSI, and high WSSG, which are strongly affected by the diameter ratio. The implications of the flow patterns for atherogenesis are enumerated.

scholarly journals Quasi-three-dimensional numerical model for flow through flexible, rigid, submerged and non-submerged vegetation

2003 ◽  
Vol 5 (3) ◽  
pp. 189-202 ◽  
Author(s):  
K. S. Erduran ◽  
V. Kutija
Keyword(s):  
Eddy Viscosity ◽  
Stokes Equations ◽  
Correction Term ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Beam Theory ◽  
Shear Stresses ◽  
Complex Flow ◽  
Drag Forces ◽  
Major Interest

The effects of the resistance caused by vegetation on flow velocity and water depth has become a major interest for ecologists and those who deal with river restoration projects. Some numerical and experimental works have been performed to analyse and formulate the drag effects induced by vegetation. Here we introduce a quasi-three-dimensional (Q3D) numerical solution, which is constructed by coupling the finite volume solution of the two-dimensional shallow water equations with a finite difference solution of Navier–Stokes equations for vertical velocity distribution. The drag forces are included in both sets of equations. Turbulence shear stresses are computed in two alternative ways: the parabolic eddy viscosity approach with a correction term introduced in this study, and a combination of the eddy viscosity and mixing length theories in the vertical direction. In order to deal with flexible vegetation, a cantilever beam theory is used to compute the deflection of the vegetation. The model COMSIM (complex flow simulations) has been developed and applied in experimental cases. The results are shown to be satisfactory.

PREDICTION OF COMPLEX FLOW PATTERNS IN INTRACRANIAL ATHEROSCLEROTIC DISEASE USING COMPUTATIONAL FLUID DYNAMICS

Neurosurgery ◽  
2007 ◽  
Vol 61 (4) ◽  
pp. 842-852 ◽  
Author(s):  
Clemens M. Schirmer ◽  
Adel M. Malek
Keyword(s):  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Atherosclerotic Disease ◽  
High Shear ◽  
Cfd Analysis ◽  
Stent Angioplasty ◽  
Complex Flow ◽  
Intracranial Atherosclerotic Disease

Abstract OBJECTIVE Although carotid and vertebral intracranial atherosclerotic disease (ICAD) can lead to both hemodynamic insufficiency and thromboembolism, its fluid dynamic properties remain undefined because of its intricate features and complex three-dimensional geometry. We used computational fluid dynamic (CFD) analysis to model the hemodynamics of symptomatic ICAD lesions. METHODS Nine ICAD lesions (six carotid, two vertebral, one middle cerebral) underwent high-resolution catheter-based digital rotational angiography. The reconstructed three-dimensional volumes of the target lesions were segmented and used to generate hybrid computational meshes. Dynamic pulsatile CFD analysis was performed using a non-Newtonian shear-dependent model of blood's viscosity. RESULTS CFD results revealed complex flow patterns within ICAD lesions with midstenotic shear rates of greater than 19,000/s, sufficiently high to induce high-shear platelet activation. Vorticity and helicity within the stenoses were followed by sudden deceleration with formation of vortex cores. Pressure gradients were significant mostly at greater than 75% stenosis with a mean time-averaged drop of 27.2 ±17.8 mmHg. Unlike the smoothly-varying helicity imparted by the three-dimensional anatomy of the intracranial circulation, poststenotic regions of ICAD lesions showed significant and rapidly fluctuating helicity and vorticity patterns, which may contribute to the propagation of platelets activated by the high shear region within the stenosis throat. Stent angioplasty restored the hemodynamic profile of ICAD lesions to within contralateral controls. CONCLUSION Patient-based symptomatic ICAD lesions studied using CFD analysis appear to harbor a hemodynamically pathological environment that favors the activation, aggregation and distal embolization of platelets and is reversed by endovascular stent angioplasty.

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