EXPERIMENTAL DATA SET NO. 8: STRATIFIED FLOW, PART II: INTERFACIAL AND WALL SHEAR STRESS

As two important parameters, the velocity of disturbance wave and the wall shear stress in annular flow are very important to solve the closed equations of the mechanical model for annular flow. In this study, the disturbance wave velocity and wall shear stress of annular flow in a vertical narrow rectangular channel with a cross section of 70 mm × 2 mm were studied. According to the experimental results, it is found that the wave velocity and wall shear stress of disturbance wave increase with increasing gas phase velocity and liquid phase velocity. Also, existing correlations for predicting the velocity of disturbance wave were summarized and evaluated using the current experimental data. A new correlation for wall shear stress based on the disturbance wave velocity has been proposed. Compared with the existing correlation for predicting wall shear stress, this new correlation can well predict the current experimental data and MAPE is only 7.32%.

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Numerical investigation of semifilled-pipe flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.956 ◽

2021 ◽

Vol 932 ◽

Author(s):

Julian Brosda ◽

Michael Manhart

Keyword(s):

Shear Stress ◽

Free Surface ◽

Wall Shear Stress ◽

Turbulent Flow ◽

Pipe Flow ◽

Flow Characteristics ◽

Streamwise Vorticity ◽

Reynolds Stresses ◽

Data Set ◽

Wall Shear

This study describes turbulent flow in a semifilled pipe with a focus on its secondary currents. To the authors’ knowledge, we provide the first highly resolved data-set for semifilled-pipe flow using direct numerical simulation. The flow parameters range from $Re_\tau =115$ , just maintaining turbulence, to moderate turbulent flow at $Re_\tau =460$ . Some of the main flow characteristics are in line with previously published results from experiments, such as the velocity-dip phenomenon, the main secondary flow and the qualitative distribution of the Reynolds stresses in the core of the flow. We observe some flow phenomena which have not yet been reported in the literature so far for this type of flow. Among those is the inner secondary cell in the mixed corner between the free surface and the pipe's wall, which plays a major role in the distribution of the wall shear stress along the perimeter. We observe that the position and extension of the inner vortex scale with the wall shear stress and those of the outer vortex scale with outer variables. For the first time, we present and discuss distributions of the complete Reynolds stress tensor and its anisotropy which gives rise to the generation of mean streamwise vorticity in a small region in the mixed corners of the pipe. Mean secondary kinetic energy, however, is generated at the free surface around the stagnation point between the inner and outer vortices. This generation mechanism is in line with a vortex dynamics mechanism proposed in the literature.

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Effects of transmural pressure and wall shear stress on LDL accumulation in the arterial wall: a numerical study using a multilayered model

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01281.2006 ◽

2007 ◽

Vol 292 (6) ◽

pp. H3148-H3157 ◽

Cited By ~ 45

Author(s):

Nanfeng Sun ◽

Nigel B. Wood ◽

Alun D. Hughes ◽

Simon A. M. Thom ◽

X. Yun Xu

Keyword(s):

Experimental Data ◽

Shear Stress ◽

Wall Shear Stress ◽

Arterial Wall ◽

Numerical Study ◽

Transmural Pressure ◽

Diffusion Reaction ◽

Model Parameters ◽

Optimization Approach ◽

Wall Shear

The accumulation of low-density lipoprotein (LDL) is recognized as one of the main contributors in atherogenesis. Mathematical models have been constructed to simulate mass transport in large arteries and the consequent lipid accumulation in the arterial wall. The objective of this study was to investigate the influences of wall shear stress and transmural pressure on LDL accumulation in the arterial wall by a multilayered, coupled lumen-wall model. The model employs the Navier-Stokes equations and Darcy's Law for fluid dynamics, convection-diffusion-reaction equations for mass balance, and Kedem-Katchalsky equations for interfacial coupling. To determine physiologically realistic model parameters, an optimization approach that searches optimal parameters based on experimental data was developed. Two sets of model parameters corresponding to different transmural pressures were found by the optimization approach using experimental data in the literature. Furthermore, a shear-dependent hydraulic conductivity relation reported previously was adopted. The integrated multilayered model was applied to an axisymmetric stenosis simulating an idealized, mildly stenosed coronary artery. The results show that low wall shear stress leads to focal LDL accumulation by weakening the convective clearance effect of transmural flow, whereas high transmural pressure, associated with hypertension, leads to global elevation of LDL concentration in the arterial wall by facilitating the passage of LDL through wall layers.

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Flow Pattern and Frictional Losses in Pulsating Pipe Flow : Part 5, Wall Shear Stress and Flow Pattern in a Laminar Flow

Bulletin of JSME ◽

10.1299/jsme1958.24.75 ◽

1981 ◽

Vol 24 (187) ◽

pp. 75-81 ◽

Cited By ~ 28

Author(s):

Munekazu OHMI ◽

Manabu IGUCHI ◽

Tateo USUI

Keyword(s):

Shear Stress ◽

Laminar Flow ◽

Wall Shear Stress ◽

Flow Pattern ◽

Pipe Flow ◽

Frictional Losses ◽

Flow Part ◽

Wall Shear

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Local and Global Geometric Influence on Steady Flow in Distal Anastomoses of Peripheral Bypass Grafts

Journal of Biomechanical Engineering ◽

10.1115/1.2073507 ◽

2005 ◽

Vol 127 (7) ◽

pp. 1087-1098 ◽

Cited By ~ 35

Author(s):

S. Giordana ◽

S. J. Sherwin ◽

J. Peiró ◽

D. J. Doorly ◽

J. S. Crane ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Steady Flow ◽

Bypass Graft ◽

Peripheral Resistance ◽

Potential Contribution ◽

Data Set ◽

Peripheral Bypass ◽

Wall Shear

We consider the effect of geometrical configuration on the steady flow field of representative geometries from an in vivo anatomical data set of end-to-side distal anastomoses constructed as part of a peripheral bypass graft. Using a geometrical classification technique, we select the anastomoses of three representative patients according to the angle between the graft and proximal host vessels (GPA) and the planarity of the anastomotic configuration. The geometries considered include two surgically tunneled grafts with shallow GPAs which are relatively planar but have different lumen characteristics, one case exhibiting a local restriction at the perianastomotic graft and proximal host whilst the other case has a relatively uniform cross section. The third case is nonplanar and characterized by a wide GPA resulting from the graft being constructed superficially from an in situ vein. In all three models the same peripheral resistance was imposed at the computational outflows of the distal and proximal host vessels and this condition, combined with the effect of the anastomotic geometry, has been observed to reasonably reproduce the in vivo flow split. By analyzing the flow fields we demonstrate how the local and global geometric characteristics influences the distribution of wall shear stress and the steady transport of fluid particles. Specifically, in vessels that have a global geometric characteristic we observe that the wall shear stress depends on large scale geometrical factors, e.g., the curvature and planarity of blood vessels. In contrast, the wall shear stress distribution and local mixing is significantly influenced by morphology and location of restrictions, particular when there is a shallow GPA. A combination of local and global effects are also possible as demonstrated in our third study of an anastomosis with a larger GPA. These relatively simple observations highlight the need to distinguish between local and global geometric influences for a given reconstruction. We further present the geometrical evolution of the anastomoses over a series of follow-up studies and observe how the lumen progresses towards the faster bulk flow of the velocity in the original geometry. This mechanism is consistent with the luminal changes in recirculation regions that experience low wall shear stress. In the shallow GPA anastomoses the proximal part of the native host vessel occludes or stenoses earlier than in the case with wide GPA. A potential contribution to this behavior is suggested by the stronger mixing that characterizes anastomoses with large GPA.

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Measurements of Velocity and Wall Shear Stress Inside a PTFE Vascular Graft Model Under Steady Flow Conditions

Journal of Biomechanical Engineering ◽

10.1115/1.2796079 ◽

1997 ◽

Vol 119 (2) ◽

pp. 187-194 ◽

Cited By ~ 44

Author(s):

F. Loth ◽

S. A. Jones ◽

D. P. Giddens ◽

H. S. Bassiouny ◽

S. Glagov ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Flow Field ◽

Steady Flow ◽

Axial Length ◽

Ptfe Graft ◽

Flow Conditions ◽

Data Set ◽

Stress Region ◽

Wall Shear

The flow field inside a model of a polytetrafluoroethylene (PTFE) canine artery end-to-side bypass graft was studied under steady flow conditions using laser-Doppler anemometry. The anatomically realistic in vitro model was constructed to incorporate the major geometric features of the in vivo canine anastomosis geometry, most notably a larger graft than host artery diameter. The velocity measurements at Reynolds number 208, based on the host artery diameter, show the flow field to be three dimensional in nature. The wall shear stress distribution, computed from the near-wall velocity gradients, reveals a relatively low wall shear stress region on the wall opposite to the graft near the stagnation point approximately one artery diameter in axial length at the midplane. This low wall shear stress region extends to the sidewalls, suture lines, and along the PTFE graft where its axial length at the midplane is more than two artery diameters. The velocity distribution inside the graft model presented here provides a data set well suited for validation of numerical solutions on a model of this type.

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Abstract 15940: Wall Shear Stress and Vorticity in Atrial Fibrillation, Pulmonary Hypertension, and Normal Atrial Anatomy Models

Circulation ◽

10.1161/circ.142.suppl_3.15940 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

David R Rutkowski ◽

Alexey Glukhov ◽

Alejandro Roldán-Alzate

Keyword(s):

Atrial Fibrillation ◽

Blood Flow ◽

Pulmonary Hypertension ◽

Shear Stress ◽

Wall Shear Stress ◽

Pulmonary Veins ◽

Atrial Volume ◽

Atrial Wall ◽

Data Set ◽

Wall Shear

Introduction: Atrial fibrillation (AF) is a common cardiac rhythm disorder that is often comorbid with pulmonary hypertension (PH) and other conditions associated with abnormal atrial pressure and/or volume overload. In the setting of atrial dilation, mechanoelectric feedback has been linked to the development of ectopic beats that trigger paroxysmal AF mainly originating from pulmonary veins (PVs). However, the precise mechanisms remain poorly understood. Here, we aimed to characterize atrial wall shear stress (WSS) and vorticity in the left atrium of AF, healthy, and at-risk for AF (PH) patient models to develop predictors of AF risk. Methods: Magnetic resonance imaging and computed tomography data (10 AF, 10 PH, and 10 healthy volunteers) were obtained retrospectively. The left atria were manually segmented from each data set. Four-dimensional flow MRI was performed on one patient to derive PV flow data. The 30 atrial geometries and PV flow conditions were used to run numerical blood flow simulations, and atrial WSS and blood flow vorticity were analyzed. Results: As seen in Figure 1, wall shear stress was highest near the PV roots and on the posterior atrial wall, the most common sources of AF triggers. Average WSS and vorticity were significantly lower in PH patients than in both the healthy (p=0.003(WSS), p=0.011(vorticity)) and AF (p=0.046(WSS), p=0.069(vorticity)) groups. Both WSS (r=-0.66) and vorticity (r=-0.68) were moderately correlated to atrial volume in the PH group. Atrial volume was significantly larger in PH (p<0.001) and AF (p<0.001) groups than in the healthy group. Conclusions: The larger atrial volumes of PH and AF patients lead to altered flow profiles and less frequently flow jet impingement on the atrial wall models, leading to abnormal vorticity and WSS profiles. These long term flow abnormalities may influence the development and/or localization of electrical abnormalities and AF; although further study is needed to confirm this hypothesis.

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