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.

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.

The Effect of Angle and Flow Rate Upon Hemodynamics in Distal Vascular Graft Anastomoses: A Numerical Model Study

1994 ◽  
Vol 116 (3) ◽  
pp. 331-336 ◽  
Author(s):  
Ding-Yu Fei ◽  
James D. Thomas ◽  
Stanley E. Rittgers
Keyword(s):  
Numerical Model ◽  
Stagnation Point ◽  
Arterial Wall ◽  
Artery Bypass ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
In Vivo Studies ◽  
Stagnation Points

Flow in distal end-to-side anastomoses of iliofemoral artery bypass grafts was simulated using a steady flow, three-dimensional numerical model. With the proximal artery occluded, anastomotic angles were varied over 20, 30, 40, 45, 50, 60 and 70 deg while the inlet Reynolds numbers were 100 and 205. Fully developed flow in the graft became somewhat skewed toward the inner wall with increasing angle for both Reynolds numbers. Separated flow regions were seen along the inner arterial wall (toe region) for angles ≥ 60 deg at Re = 100 and for angles ≥ 45 deg at Re = 205 while a stagnation point existed along the outer arterial wall (floor region) for all cases which moved downstream relative to the toe of the anastomosis with decreasing angles. Normalized shear rates (NSR) along the arterial wall varied widely throughout the anastomotic region with negative values seen in the separation zones and upstream of the stagnation points which increased in magnitude with angle. The NSR increased with distance downstream of the stagnation point and with magnitudes which increased with the angle. Compared with observations from chronic in vivo studies, these results appear to support the hypothesis of greater intimal hyperplasia occurring in regions of low fluid shear.

Characteristics of Turbulent Three-Dimensional Wall Jets

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
M. Agelin-Chaab ◽  
M. F. Tachie
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Orthogonal Decomposition ◽  
The Self ◽  
Shear Stresses ◽  
Spread Rate ◽  
Similar Region ◽  
Self Similar ◽  
Proper Orthogonal

Three-dimensional turbulent wall jet was investigated using a particle image velocimetry technique. Three Reynolds numbers based on the jet exit velocity and diameter of 5000, 10,000, and 20,000 were studied. Profiles of the mean velocities, turbulence intensities, and Reynolds shear stresses as well as two-point velocity correlations and proper orthogonal decomposition analyses were used to document the salient features of the wall jets. The decay and spread rates are independent of Reynolds numbers in the self-similar region. The estimated values of 1.15, 0.054, and 0.255 for the decay rate, wall-normal spread rate, and lateral spread rate, respectively, are within the range of values reported in the literature. The two-point correlation analysis showed that the inclination of the streamwise velocity correlation contours in the inner layer is 11±3 deg in the wall region, which is similar to those of canonical turbulent boundary layers. The results from the proper orthogonal decomposition indicate that low-order modes contribute more to the turbulence statistics in the self-similar region than in the developing region. The Reynolds shear stresses are the biggest benefactors of the low-order mode contribution while the wall-normal turbulence intensities are the least.

Global stability of multiple solutions in plane sudden-expansion flow

2012 ◽  
Vol 702 ◽  
pp. 378-402 ◽  
Author(s):  
Daniel Lanzerstorfer ◽  
Hendrik C. Kuhlmann
Keyword(s):  
Secondary Flow ◽  
Mirror Symmetry ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Secondary Flows ◽  
Sudden Expansion ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Large Expansion

AbstractThe two-dimensional, incompressible flow in a plane sudden expansion is investigated numerically for a systematic variation of the geometry, covering expansion ratios (steps-to-outlet heights) from $0. 25$ to $0. 95$. By means of a three-dimensional linear stability analysis global temporal modes are scrutinized. In a symmetric expansion the primary bifurcation is stationary and two-dimensional, breaking the mirror symmetry with respect to the mid-plane. The secondary asymmetric flow experiences a secondary instability to different three-dimensional modes, depending on the expansion ratio. For a moderately asymmetric expansion only one of the two secondary flows (the connected branch) is realized at low Reynolds numbers. Since the perturbed secondary flow does not deviate much from the symmetric secondary flow, both secondary stability boundaries are very close to each other. For very small and very large expansion ratios an asymptotic behaviour is found for suitably scaled critical Reynolds numbers and wavenumbers. Representative instabilities are analysed in detail using an a posteriori energy transfer analysis to reveal the physical nature of the instabilities. Depending on the geometry, pure centrifugal and elliptical amplification processes are identified. We also find that the basic flow can become unstable due to the effects of flow deceleration, streamline convergence and high shear stresses, respectively.

scholarly journals NONSYMMETRIC BRANCHING OF FLUID FLOWS IN 3D VESSELS

2018 ◽  
Vol 59 (4) ◽  
pp. 533-561
Author(s):  
N. C. OVENDEN ◽  
F. T. SMITH
Keyword(s):  
Three Dimensional ◽  
Fluid Flows ◽  
Outer Wall ◽  
Reynolds Numbers ◽  
Arbitrary Cross Section ◽  
Shear Stresses ◽  
Flux Change ◽  
End Pressures ◽  
Branching Flow ◽  
Unsteady Effects

Nonsymmetric branching flow through a three-dimensional (3D) vessel is considered at medium-to-high flow rates. The branching is from one mother vessel to two or more daughter vessels downstream, with laminar steady or unsteady conditions assumed. The inherent 3D nonsymmetry is due to the branching shapes themselves, or the differences in the end pressures in the daughter vessels, or the incident velocity profiles in the mother. Computations based on lattice-Boltzmann methodology are described first. A subsequent analysis focuses on small 3D disturbances and increased Reynolds numbers. This reduces the 3D problem to a two-dimensional one at the outer wall in all pressure-driven cases. As well as having broader implications for feeding into a network of vessels, the findings enable predictions of how much swirling motion in the cross-plane is generated in a daughter vessel downstream of a 3D branch junction, and the significant alterations provoked locally in the shear stresses and pressures at the walls. Nonuniform incident wall-shear and unsteady effects are examined. A universal asymptotic form is found for the flux change into each daughter vessel in a 3D branching of arbitrary cross-section with a thin divider.

Recirculation Zones in a Cylindrical Container

1998 ◽  
Vol 120 (4) ◽  
pp. 680-684 ◽  
Author(s):  
Craig C. Jahnke ◽  
Daniel T. Valentine
Keyword(s):  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Cylindrical Container ◽  
Characteristic Parameters ◽  
Stagnation Points ◽  
Rotation Rates ◽  
Columnar Vortex ◽  
Axis Of Rotation ◽  
Recirculation Zones ◽  
End Wall

The flow field induced inside a cylindrical container by the rotation of the two end walls is described. It is shown that stagnation points leading to separation bubbles occur on the axis of rotation and/or the bottom end wall for certain ranges of the characteristic parameters; the Reynolds number, the aspect ratio of the container, and the ratio of the rotation rates of the end walls. Flow fields in a container of aspect ratio 2.0 are examined for Reynolds numbers from 100 to 3000 and ratios of the rotation rates of the top and bottom end walls from −0.10 to 1.0. For a range of ratios of the rotation rates of the top and bottom end walls and Reynolds numbers it is shown that ring vortices surrounding a columnar vortex core exist.

Characteristics of a Single Sensor Fiber-Coupled 3D PIV for Reacting Flow-Fields

2021 ◽  
Author(s):  
Cal Rising ◽  
Jonathan Reyes ◽  
Kareem Ahmed
Keyword(s):  
High Speed ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Flow Fields ◽  
Velocity Fields ◽  
Diagnostic Approach ◽  
Reacting Flow ◽  
Shear Stresses ◽  
Piv Measurement ◽  
Single Sensor

Abstract Tomographic particle image velocimetry (Tomo-PIV) has become a standard tool for capturing a three-dimensional velocity fields in non-reacting flows. However, the diagnostic approach can become costly and challenging to implement when extended to applications which require high-speed cameras. This limitation has led to the use of fiber wound bundles to allow for multiple views to be captured on a single camera sensor. Additionally, employing this diagnostic approach on reacting flow fields becomes more complex as the introduction of the flame causes additional luminosity and optical distortion which impacts the particle field reconstruction. The current work seeks to validate and determine the limitations when utilizing a single sensor fiber coupled approach for capturing Tomo-PIV data on a reacting flow-field. A premixed propane (C3H8) and air Bunsen burner flame is utilized to examine if the single sensor approach can meet the parameters for acceptable reconstruction based on previous research. The resulting velocity fields are then compared to a traditional PIV measurement to assess the deviation of the single sensor approach from a standard velocimetry measurement approach. It is demonstrated that there is strong agreement between the velocity and vorticity for the average flow-fields, however when comparing the Reynolds Shear Stresses a significant deviation is revealed. The deviation is attributed to strong velocity fluctuations occurring within the instantaneous Tomo-PIV data, which creates a significant divergence between the measurement techniques on an instantaneous basis. This demonstrates that while the approach can obtain reliable velocity and vorticity statistics, there is significant limitations in calculating second-order turbulence statistics. Thus, revealing that there is a tradeoff between the ability to extract the full velocity gradient tensor and the extent of the turbulence related analysis which can be reliably performed.

scholarly journals Flow characteristics analysis for flow past the porous spheres: wake structures and drag force coefficients

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Likun Ma ◽  
Sina Kashanj ◽  
Shuliang Xu ◽  
Mao Ye ◽  
David Nobes
Keyword(s):  
Flow Characteristics ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Solid Sphere ◽  
Flow Fields ◽  
Stagnation Points ◽  
Flow Past ◽  
Characteristics Analysis ◽  
Permeable Sphere ◽  
Porous Spheres

Flow past a permeable sphere is different from that of a solid sphere due to the penetration of the fluid within porous structures, which can arise a change of flow fields. In this work, flow past porous spheres with Darcy numbers (Da) ranging from [0,10−3 ] were measured using planar Particle Image Velocimetry (PIV). The whole flow fields, including both leading edge and trailing edge, were captured at six different Reynolds numbers (Re) varying from 400 to 1400. Time-average flow fields were calculated based on instantaneous flow fields within fully-developed stages. Local minimum method was used to search for stagnation point positions. The results show positions of stagnation points are nearly proportional to the logarithm of Re. For most porous spheres, positions of stagnation points are extended to farther downstream positions than that of a solid sphere. However, at some certain Darcy numbers, ranging from 5 ∗ 10−6 to 2 ∗ 10−5, positions of stagnation points are closer to the sphere centers than that of an impermeable one.

Imaging of platinum-shadowed macromolecular complexes in dark field

1984 ◽  
Vol 42 ◽  
pp. 146-147
Author(s):  
D.W. Andrews ◽  
F.P. Ottensmeyer
Keyword(s):  
Thin Film ◽  
Three Dimensional ◽  
Average Diameter ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Macromolecular Complexes ◽  
Average Mass ◽  
Topological Features ◽  
Projection Images

Shadowing with heavy metals has been used for many years to enhance the topological features of biological macromolecular complexes. The three dimensional features present in directionaly shadowed specimens often simplifies interpretation of projection images provided by other techniques. One difficulty with the method is the relatively large amount of metal used to achieve sufficient contrast in bright field images. Thick shadow films are undesirable because they decrease resolution due to an increased tendency for microcrystalline aggregates to form, because decoration artefacts become more severe and increased cap thickness makes estimation of dimensions more uncertain.The large increase in contrast provided by the dark field mode of imaging allows the use of shadow replicas with a much lower average mass thickness. To form the images in Fig. 1, latex spheres of 0.087 μ average diameter were unidirectionally shadowed with platinum carbon (Pt-C) and a thin film of carbon was indirectly evaporated on the specimen as a support.

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