The Wall Shear Stress Vector: Methods for Characterising Truly Disturbed Flow

2012 ◽  
Author(s):  
Véronique Peiffer ◽  
Peter D. Weinberg ◽  
Spencer J. Sherwin
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Dynamic ◽  
Flow Characteristics ◽  
New Method ◽  
Molecular Signaling ◽  
Stress Vector ◽  
Cfd Simulations ◽  
Disturbed Flow ◽  
Wall Shear

Haemodynamic stresses acting on the arterial wall may play an important role in the initiation and development of atherosclerosis, and in particular are likely to explain its focal occurrence. Computational fluid dynamic (CFD) simulations of blood flow in arteries have been widely used to investigate this relation and a variety of metrics have been derived to link flow characteristics with lesion prevalence [1]. Although the initial focus was on the magnitude of the time-averaged wall shear stress (TAWSS), an oscillatory shear index (OSI) was subsequently introduced “to describe the shear stress acting in directions other than the direction of the temporal mean shear stress vector” [2]. Biological evidence suggests that flow without a definite direction, in contrast to shear with a clear direction (whether resulting from steady or pulsatile flow), causes sustained molecular signaling of pro-inflammatory and proliferative pathways [3]. Although the OSI has frequently been used to quantify the extent of disturbed flow, we emphasise that no singular metric can fully characterise the flow environment; in particular, we and other research groups [4] note that OSI and other similar metrics are unable to distinguish between simple uniaxial flows (which can be purely forward flowing or reversing) and multi-directional flows, which we term “truly disturbed”. We propose a new method that has this potential, and which complements existing metrics. The new method may help investigations of the importance of flow directionality.

scholarly journals Assessing Bioinspired Topographies for their Antifouling Potential Control Using Computational Fluid Dynamics (CFD)

2018 ◽  
Vol 152 ◽  
pp. 02004 ◽  
Author(s):  
Jacky Ling ◽  
Felicia Wong Yen Myan
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Extended Period ◽  
Slip Boundary Condition ◽  
Shear Stresses ◽  
Cfd Simulations ◽  
Potential Control ◽  
Slip Boundary ◽  
Computational Fluid Dynamics Cfd ◽  
Wall Shear

Biofouling is the accumulation of unwanted material on surfaces submerged or semi submerged over an extended period. This study investigates the antifouling performance of a new bioinspired topography design. A shark riblets inspired topography was designed with Solidworks and CFD simulations were antifouling performance. The study focuses on the fluid flow velocity, the wall shear stress and the appearance of vortices are to be noted to determine the possible locations biofouling would most probably occur. The inlet mass flow rate is 0.01 kgs-1 and a no-slip boundary condition was applied to the walls of the fluid domain. Simulations indicate that Velocity around the topography averaged at 7.213 x 10-3 ms-1. However, vortices were observed between the gaps. High wall shear stress is observed at the peak of each topography. In contrast, wall shear stress is significantly low at the bed of the topography. This suggests the potential location for the accumulation of biofouling. Results show that bioinspired antifouling topography can be improved by reducing the frequency of gaps between features. Linear surfaces on the topography should also be minimized. This increases the avenues of flow for the fluid, thus potentially increasing shear stresses with surrounding fluid leading to better antifouling performance.

Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Matthew D. Ford ◽  
Ugo Piomelli
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
High Frequency ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Disturbed Flow ◽  
Frequency Fluctuations ◽  
Wall Shear ◽  
Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

Distribution of Mass Transfer Rate and Wall Shear Stress Behind Simple Rectangular Stenosis in Pulsating Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 47-54 ◽  
Author(s):  
R. Yamaguchi
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Transfer Rate ◽  
Schmidt Number ◽  
Fluid Dynamic ◽  
Mass Transfer Rate ◽  
Pulsating Flow ◽  
Flow Through ◽  
Wall Shear

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.

Analysis of Flow and Wall Shear Stress in Curvature Induced Dorsal Aneurysms: Effect of Arterial Curvature

2009 ◽  
Author(s):  
Arun Ramu ◽  
Guo-Xiang Wang
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Dynamic ◽  
Cerebral Arteries ◽  
Cerebral Aneurysms ◽  
Morbidity Rate ◽  
Mortality And Morbidity ◽  
Wall Shear ◽  
Primary Velocity ◽  
The Impact

Intracranial aneurysms are abnormal enlargement in the walls of cerebral arteries. The rupture of aneurysms is the leading cause of subarachnoid hemorrhage (SAH), with a high mortality and morbidity rate. A majority of saccular cerebral aneurysms occur at sites of arterial bifurcations. However, a good percentage of aneurysms are curvature induced and are found along the cavernous arterial segment. The occurrence of such non branching aneurysms, clinically called dorsal aneurysms, can be related to the increased wall shear stress at the curved arteries. The rupture of aneurysms usually occurs at the dome region, which is subjected to reduced wall shear stress (wss) owing to low re-circulating flow. Hence it is important to understand the impact of arterial curvature on the WSS distribution along the dome of aneurysms. Previously, studies have not taken into account the aspect of low WSS along the dome region. In the present 3-d computational fluid dynamic approach, we investigate the impact of varying arterial curvature on spherical dorsal aneurysms. The primary velocity patterns, the WSS distribution along the dome of the aneurysm and the area of increased WSS have been quantified for steady flow conditions.

Entropy hemodynamics particle-fluid suspension model through eccentric catheterization for time-variant stenotic arterial wall: Catheter injection

2019 ◽  
Vol 16 (11) ◽  
pp. 1950164 ◽  
Author(s):  
Kh. S. Mekheimer ◽  
A. Z. Zaher ◽  
A. I. Abdellateef
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Distribution ◽  
Wall Shear Stress ◽  
Outer Cylinder ◽  
Flow Characteristics ◽  
Two Phase ◽  
Eccentric Cylinder ◽  
Wall Shear ◽  
Suspension Model

Catheterization has an imperative rule in heat transfer investigations, which are frequently applied to analyze and deal with the heart transfer studies. Here, the entering of a catheter adjusts the flow of the blood and it affects the hemodynamic status in the artery region. In practical clinical cases, catheters cannot be precisely concentric with the artery. The impartial of this work is to investigate the behavior of a blood streaming characteristics, in the case of injecting the catheter eccentrically all the way through a stenotic overlapping artery. In this paper, we consider the heat transfer within the presence of blood corpuscle which has been characterized by a macroscopic two-phase model (i.e. a suspension of erythrocytes in plasma). The model here considers the blood fluid as a liquid fluid with adjourned particles in the gap bounded by the eccentric cylinder. The inside cylinder is identically rigid demonstrating the movable thin catheter and kept at constant temperature, where the outer cylinder is a taper cylinder demonstrating the artery that has overlapping stenosis and it is cooled and maintained at zero temperature. The coupled differential equations for both fluid (plasma) and particle (erythrocyte) phases have been solved. The expressions for the flow characteristics, namely, the flow rate, the impedance (resistance to flow), the wall shear stress and the temperature distribution, have been derived. The model is very useful in medicine, where the hemodynamic speed is higher for eccentric case than that of concentric one. Also, the temperature distribution and the entropy generation in the state of eccentric position are higher than in the case of the concentric position. A significant increase in the magnitude of the impedance and the wall shear stress occurs for an increase in the hematocrit, C for diseased blood.

scholarly journals Investigation of blood flow through an artery in the presence of overlapping stenosis

2017 ◽  
Vol 14 (1) ◽  
pp. 39-46 ◽  
Author(s):  
K. Maruthi Prasad ◽  
S. Thulluri ◽  
M. V. Phanikumari
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Couple Stress ◽  
Flow Characteristics ◽  
Couple Stress Fluid ◽  
Flow Equations ◽  
Wall Shear ◽  
Fluid Parameters

The effects of an overlapping stenosis on blood flow characteristics in an artery have been studied. Blood has been represented by a couple stress fluid. The flow equations have been linearised and the expressions for pressure drop, resistance to the flow and wall shear stress have been derived. The results are shown graphically. It is observed that the resistance to the flow, pressure drop and wall shear stress increases with height and length of the stenosis. And it is noticed that the resistance to the flow and pressure drop decreases with couple stress fluid parameters. But wall shear stress increases with couple stress fluid parameters.

Spatial comparison between wall shear stress measures and porcine arterial endothelial permeability

2004 ◽  
Vol 286 (5) ◽  
pp. H1916-H1922 ◽  
Author(s):  
Heather A. Himburg ◽  
Deborah M. Grzybowski ◽  
Andrew L. Hazel ◽  
Jeffrey A. LaMack ◽  
Xue-Mei Li ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Evans Blue ◽  
Fluid Dynamic ◽  
Endothelial Permeability ◽  
Blue Dye ◽  
Evans Blue Dye ◽  
Wall Shear ◽  
And Function

A better understanding of how hemodynamic factors affect the integrity and function of the vascular endothelium is necessary to appreciate more fully how atherosclerosis is initiated and promoted. A novel technique is presented to assess the relation between fluid dynamic variables and the permeability of the endothelium to macromolecules. Fully anesthetized, domestic swine were intravenously injected with the albumin marker Evans blue dye, which was allowed to circulate for 90 min. After the animals were euthanized, silicone casts were made of the abdominal aorta and its iliac branches. Pulsatile flow calculations were subsequently made in computational regions derived from the casts. The distribution of the calculated time-dependent wall shear stress in the external iliac branches was directly compared on a point-by-point basis with the spatially varying in vivo uptake of Evans blue dye in the same arteries. The results indicate that in vivo endothelial permeability to albumin decreases with increasing time-average shear stress over the normal range. Additionally, endothelial permeability increases slightly with oscillatory shear index.

scholarly journals Identification of the haemodynamic environment permissive for plaque erosion

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Michael McElroy ◽  
Yongcheol Kim ◽  
Giampaolo Niccoli ◽  
Rocco Vergallo ◽  
Alexander Langford-Smith ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Dynamic ◽  
Stress Gradient ◽  
Plaque Erosion ◽  
Reference Segment ◽  
Stress Maximum ◽  
Relative Residence Time ◽  
Coronary Syndromes ◽  
Wall Shear

AbstractEndothelial erosion of atherosclerotic plaques is the underlying cause of approximately 30% of acute coronary syndromes (ACS). As the vascular endothelium is profoundly affected by the haemodynamic environment to which it is exposed, we employed computational fluid dynamic (CFD) analysis of the luminal geometry from 17 patients with optical coherence tomography (OCT)-defined plaque erosion, to determine the flow environment permissive for plaque erosion. Our results demonstrate that 15 of the 17 cases analysed occurred on stenotic plaques with median 31% diameter stenosis (interquartile range 28–52%), where all but one of the adherent thrombi located proximal to, or within the region of maximum stenosis. Consequently, all flow metrics related to elevated flow were significantly increased (time averaged wall shear stress, maximum wall shear stress, time averaged wall shear stress gradient) with a reduction in relative residence time, compared to a non-diseased reference segment. We also identified two cases that did not exhibit an elevation of flow, but occurred in a region exposed to elevated oscillatory flow. Our study demonstrates that the majority of OCT-defined erosions occur where the endothelium is exposed to elevated flow, a haemodynamic environment known to evoke a distinctive phenotypic response in endothelial cells.

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