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.

scholarly journals Plaque morphology in acute symptomatic intracranial atherosclerotic disease

2020 ◽  
pp. jnnp-2020-325027
Author(s):  
Thomas W Leung ◽  
Li Wang ◽  
Xinying Zou ◽  
Yannie Soo ◽  
Yuehua Pu ◽  
...  
Keyword(s):  
Ischaemic Stroke ◽  
Three Dimensional ◽  
Morphological Features ◽  
Atherosclerotic Disease ◽  
Sensitivity Analyses ◽  
Plaque Morphology ◽  
Stroke Subtype ◽  
Anterior Circulation ◽  
Intracranial Atherosclerotic Disease ◽  
Ulcerative Lesions

BackgroundIntracranial atherosclerotic disease (ICAD) is globally a major ischaemic stroke subtype with high recurrence. Understanding the morphology of symptomatic ICAD plaques, largely unknown by far, may help identify vulnerable lesions prone to relapse.MethodsWe prospectively recruited patients with acute ischaemic stroke or transient ischaemic attack attributed to high-grade ICAD (60%–99% stenosis). Plaque morphological parameters were assessed in three-dimensional rotational angiography, including surface contour, luminal stenosis, plaque length/thickness, upstream shoulder angulation, axial/longitudinal plaque distribution and presence of adjoining branch atheromatous disease (BAD). We compared morphological features of smooth, irregular and ulcerative plaques and correlated them with cerebral ischaemic lesion load downstream in MRI.ResultsAmong 180 recruited patients (median age=60 years; 63.3% male; median stenosis=75%), plaque contour was smooth (51 (28.3%)), irregular (101 (56.1%)) or ulcerative (28 (15.6%)). Surface ulcers were mostly at proximal (46.4%) and middle one-third (35.7%) of the lesions. Most (84.4%) plaques were eccentric, and half had their maximum thickness over the distal end. Ulcerative lesions were thicker (medians 1.6 vs 1.3 mm; p=0.003), had steeper upstream shoulder angulation (56.2° vs 31.0°; p<0.001) and more adjoining BAD (83.3% vs 57.0%; p=0.033) than non-ulcerative plaques. Ulcerative plaques were significantly associated with coexisting acute and chronic infarcts downstream (35.7% vs 12.5%; adjusted OR 4.29, 95% CI 1.65 to 11.14, p=0.003). Sensitivity analyses in patients with anterior-circulation ICAD lesions showed similar results in the associations between the plaque types and infarct load.ConclusionsUlcerative intracranial atherosclerotic plaques were associated with vulnerable morphological features and had a higher cumulative infarct load downstream.

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.

The Role of Three-Dimensional Interactions in Fluidic Control of Shock-Induced Separation on a Transonic Turbine Blade

2015 ◽  
Author(s):  
Chiara Bernardini ◽  
Craig Sacco ◽  
Jeffrey P. Bons ◽  
Jen-Ping Chen ◽  
Francesco Martelli
Keyword(s):  
Fluid Dynamic ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Vortex Generator ◽  
Control Performance ◽  
Complex Flow ◽  
Discrete Vortex ◽  
Rans Simulations ◽  
Vortex Generator Jets ◽  
Highly Loaded

An experimental and numerical investigation is conducted to assess the fluid dynamic mechanisms of control by vortex-generator jets for shock-induced separation in a highly loaded low pressure turbine (LPT) blade. Two- and three-dimensional steady RANS computations are performed to evaluate their ability to reproduce the main features of such a complex flow. The test blade is part of a compressible LPT cascade that exhibits shock-induced separation at an exit Mach number of 0.8. Active flow control is implemented through a spanwise row of discrete vortex-generator jets (VGJs) located on the suction surface. The control performance of VGJs in these transonic conditions has an optimum blowing ratio beyond which losses increase. Three-dimensionalities in the flow field are established by discrete VGJ-boundary layer interaction as suggested by Particle-Image Velocimetry (PIV) acquisitions at different spanwise locations. Blade pressure distributions and wake total pressure losses are acquired to evaluate the control performance and compared with calculations. Two-dimensional numerical investigations by RANS simulations suggest that the effect of increased expansion over the passage is a product of massflow injection only. Three-dimensional RANS results are interrogated to give a more detailed representation of the flow features around the jets, such as the jet vortex dynamics and spanwise modulation of the potential field. The analysis of this experimental and numerical information identifies the mechanisms contributing to the performance of skewed jets for control of shock induced separation in a highly loaded LPT blade. The results provide indications on the accuracy of RANS simulations, identifying the challenges of using RANS (2D or 3D) to solve such complex flows.

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.

scholarly journals Whole-brain magnetic resonance imaging of plaque burden and lenticulostriate arteries in patients with different types of stroke

2019 ◽  
Vol 12 ◽  
pp. 175628641983329 ◽  
Author(s):  
Fang Wu ◽  
Qian Zhang ◽  
Kai Dong ◽  
Jiangang Duan ◽  
Xiaoxu Yang ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Vessel Wall ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Brain Magnetic Resonance Imaging ◽  
Atherosclerotic Disease ◽  
Plaque Burden ◽  
Control Group ◽  
Whole Brain ◽  
Intracranial Atherosclerotic Disease

Background: Large-vessel atherosclerotic disease is an important pathogenesis of deep-perforator infarction (DPI). However, altered vessel walls of intracranial large arteries and distribution of small arteries in DPI are unclear because of the limited resolution of current imaging techniques. In this study the intracranial plaque burden and lenticulostriate artery (LSA) distribution in patients with recent DPI and non-DPI using whole-brain vessel-wall imaging (WB-VWI) were investigated. Methods: A total of 44 patients with recent DPI (23 patients) or non-DPI (21 patients) due to intracranial atherosclerotic disease were prospectively enrolled. WB-VWI was performed in all the patients using a three-dimensional T1-weighted vessel-wall magnetic resonance technique. Hemispheres with DPI and non-DPI were considered as the DPI group and non-DPI group, respectively. Hemispheres without a history of stroke were the control group. The intracranial plaque burden was compared between the DPI and non-DPI groups. The number and length of visualized LSA branches among DPI, non-DPI, and control groups were also evaluated. Results: A total of 77 hemispheres were analyzed (23 in the DPI group, 21 in the non-DPI group, and 33 in the control group). Plaque burden was lower ( p = 0.047) in the DPI group (82.0 ± 45.9 mm3) compared with the non-DPI group (130.9 ± 90.3 mm3). There was a significant reduction ( p = 0.002) in length of visualized LSA branches in the DPI group (74.1 ± 21.7 mm) compared with the control group (104.6 ± 33.3 mm). Conclusions: WB-VWI enables the combination of vessel-wall and LSA imaging in one image setting, which can provide information about plaque burden and LSA distribution.

Thermo-Fluid-Dynamic Diagnostics in Multiple-Intersection Flow Network Using IR Thermometry and DPIV

2003 ◽  
Author(s):  
Herchang Ay ◽  
Chih-Hao Chou ◽  
Bing-Yi Chen
Keyword(s):  
Heat Transfer ◽  
Vascular System ◽  
Fluid Dynamic ◽  
Local Heat Transfer ◽  
Flow Patterns ◽  
Flow Networks ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Flip Flop ◽  
Flow Network

A multiple-intersecting flow network is common in biological and industrial systems such as the human vascular system, the internal coolant passage of turbine blade inside gas turbine engine, the liquid cooling channel inside electronic modules. An infrared thermovision system is used to map the detail local convective heat transfer coefficients for the multiple-intersection flow network consisting of a 30° intersection angle. In addition, a digital particle image velocimetry (DPIV) system had been developed to measure instantaneous and ensemble-averaged flow fields in the multiple-intersection flow networks. The flow at each intersection is characterizes by a collision of two flow streams, resulting in vortices on the two sides of the diamond-shaped pin in the post-intersecting region of the network. It is noticed that the vortex at one side increases, at the same time the vortex at the other side decreases with the flip-flop flow at the exit end of the flow network. The study also found the vortex ring places on interlacing surface of the downstream-half of the diamond-shaped pin between the two longitudinal rows. The complex flow patterns are found to play an important part in the local heat transfer performance. The main effort of the present study is attempt to interpret the DPIV measurement results to understand the detailed flow patterns inside the multiple-intersection flow networks and the heat transfer data using an infrared thermovision system.

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.

Design and Fabrication of a Constant Shear Microfluidic Network for Tissue Engineering

2004 ◽  
Vol 820 ◽  
Author(s):  
E.J. Weinberg ◽  
J.T. Borenstein ◽  
M.R. Kaazempur-Mofrad ◽  
B. Orrick ◽  
J.P. Vacanti
Keyword(s):  
Tissue Engineering ◽  
Blood Flow ◽  
Shear Stress ◽  
Endothelial Cell ◽  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cell Behavior

AbstractRecent progress in microfabrication of biodegradable materials has resulted in the development of a three-dimensional construct suitable for use as a scaffold for engineering blood vessel networks. These networks are designed to replicate the critical fluid dynamic properties of physiological systems such as the microcirculation within a vital organ. Ultimately, these 3D microvascular constructs will serve as a framework for population with organ-specific cells for applications in organ assist and organ replacement. This approach for tissue engineering utilizes highly engineered designs and microfabrication technology to assemble cells in three-dimensional constructs which have physiological values for properties such as mechanical strength, oxygen, nutrient and waste transport, and fluidic parameters such as flow volume and pressure.Three-dimensional networks with appropriate values for blood flow velocity, pressure drop and hematocrit distribution have been designed and fabricated using replica molding techniques, and populated with endothelial cells for long-term microfluidic cell culture. One critical aspect of the fluid dynamics of these systems is the shear stress exerted by blood flow at the walls of the vessel; a key parameter because of well-known mechanotransduction phenomena from mechanical shear forces which govern endothelial cell behavior. In this work, we report the design and construction of three-dimensional microfluidic constructs for tissue engineering which have uniform wall shear stress throughout the network. This type of control over the shear stress offers several advantages over earlier approaches, including more uniform seeding, more rapid achievement of confluent coatings, and better control over endothelial cell behavior for in vitro and in vivo studies.

scholarly journals The Effect of Depth on Drag During the Streamlined Glide: A Three-Dimensional CFD Analysis

2012 ◽  
Vol 33 (1) ◽  
pp. 55-62 ◽  
Author(s):  
Maria Novais ◽  
António Silva ◽  
Vishveshwar Mantha ◽  
Rui Ramos ◽  
Abel Rouboa ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Hydrodynamic Drag ◽  
Cfd Analysis ◽  
Three Dimensional Model ◽  
Commercial Code ◽  
Elite Level ◽  
Computation Fluid Dynamic

The Effect of Depth on Drag During the Streamlined Glide: A Three-Dimensional CFD AnalysisThe aim of this study was to analyze the effects of depth on drag during the streamlined glide in swimming using Computational Fluid Dynamics. The Computation Fluid Dynamic analysis consisted of using a three-dimensional mesh of cells that simulates the flow around the considered domain. We used the K-epsilon turbulent model implemented in the commercial code Fluent® and applied it to the flow around a three-dimensional model of an Olympic swimmer. The swimmer was modeled as if he were gliding underwater in a streamlined prone position, with hands overlapping, head between the extended arms, feet together and plantar flexed. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient and the drag force was calculated for velocities ranging from 1.5 to 2.5 m/s, in increments of 0.50m/s, which represents the velocity range used by club to elite level swimmers during the push-off and glide following a turn. The swimmer model middle line was placed at different water depths between 0 and 1.0 m underwater, in 0.25m increments. Hydrodynamic drag decreased with depth, although after 0.75m values remained almost constant. Water depth seems to have a positive effect on reducing hydrodynamic drag during the gliding. Although increasing depth position could contribute to decrease hydrodynamic drag, this reduction seems to be lower with depth, especially after 0.75 m depth, thus suggesting that possibly performing the underwater gliding more than 0.75 m depth could not be to the benefit of the swimmer.

scholarly journals Performance of Partial and Cavity Type Squealer Tip of a HP Turbine Blade in a Linear Cascade

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Levent Kavurmacioglu ◽  
Hidir Maral ◽  
Cem Berk Senel ◽  
Cengiz Camci
Keyword(s):  
Turbine Blade ◽  
Flow Structure ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Axial Flow ◽  
Numerical Calculations ◽  
Complex Flow ◽  
Parametric Generation ◽  
Linear Cascade ◽  
Blade Tip

Three-dimensional highly complex flow structure in tip gap between blade tip and casing leads to inefficient turbine performance due to aerothermal loss. Interaction between leakage vortex and secondary flow structures is the substantial source of that loss. Different types of squealer tip geometries were tried in the past, in order to improve turbine efficiency. The current research deals with comparison of partial and cavity type squealer tip concepts for higher aerothermal performance. Effects of squealer tip have been examined comprehensively for an unshrouded HP turbine blade tip geometry in a linear cascade. In the present paper, flow structure through the tip gap was comprehensively investigated by computational fluid dynamic (CFD) methods. Numerical calculations were obtained by solving three-dimensional, incompressible, steady, and turbulent form of the Reynolds-averaged Navier-Stokes (RANS) equations using a general purpose and three-dimensional viscous flow solver. The two-equation turbulence model, shear stress transport (SST), has been used. The tip profile belonging to the Pennsylvania State University Axial Flow Turbine Research Facility (AFTRF) was used to create an extruded solid model of the axial turbine blade. For identifying optimal dimensions of squealer rim in terms of squealer height and squealer width, our previous studies about aerothermal investigation of cavity type squealer tip were utilized. In order to obtain the mesh, an effective parametric generation has been utilized using a multizone structured mesh. Numerical calculations indicate that partial and cavity squealer designs can be effective to reduce the aerodynamic loss and heat transfer to the blade tip. Future efforts will include novel squealer shapes for higher aerothermal performance.

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