scholarly journals Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

2020 ◽  
Vol 61 (2) ◽  
Author(s):  
Andreas Bauer ◽  
Maximilian Bopp ◽  
Suad Jakirlic ◽  
Cameron Tropea ◽  
Axel Joachim Krafft ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Transitional Flow ◽  
Flow Conditions ◽  
Wall Shear

Analysis of Laminar Mixed Convective Plumes Along Vertical Adiabatic Surfaces

1984 ◽  
Vol 106 (3) ◽  
pp. 552-557 ◽  
Author(s):  
K. V. Rao ◽  
B. F. Armaly ◽  
T. S. Chen
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Vertical Surface ◽  
Stream Velocity ◽  
Thermal Source ◽  
Flow Conditions ◽  
Velocity Overshoot ◽  
Wall Shear ◽  
Prandtl Numbers

Laminar mixed forced and free convection from a line thermal source imbedded at the leading edge of an adiabatic vertical surface is analytically investigated for the cases of buoyancy assisting and buoyancy opposing flow conditions. Temperature and velocity distributions in the boundary layer adjacent to the adiabatic surface are presented for the entire range of the buoyancy parameter ξ (x) = Grx/Rex5/2 from the pure forced (ξ(x) = 0) to the pure free (ξ(x) = ∞) convection regime for fluids having Prandtl numbers of 0.7 and 7.0. For buoyancy-assisting flow, the velocity overshoot, the temperature, and the wall shear stress increase as the plume’s strength increases. On the other hand, the velocity overshoot, the wall shear stress, and the temperature decrease as the free-stream velocity increases. For buoyancy opposing flow, the velocity and wall shear stress decrease but the temperature increases as the plume’s strength increases.

Time-dependent rheological behavior of blood at low shear in narrow vertical tubes

1993 ◽  
Vol 265 (2) ◽  
pp. H553-H561 ◽  
Author(s):  
C. Alonso ◽  
A. R. Pries ◽  
P. Gaehtgens
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shear Flow ◽  
Apparent Viscosity ◽  
Flow Behavior ◽  
Time Dependent ◽  
Flow Conditions ◽  
Wall Shear ◽  
Vertical Tubes ◽  
Low Shear

The time-dependent flow behavior of normal human blood after a sudden reduction of wall shear stress from 5,000 mPa to a low level (2-100 mPa) was studied during perfusion of vertical tubes (internal diam 28-101 microns) at constant driving pressures. Immediately after the implementation of low-shear flow conditions the concentration of red blood cells (RBCs) near the tube wall started to decrease, and marginal plasma spaces developed as a result of the assembly of RBC aggregates. This was associated with a time-dependent increase of flow velocity by up to 200% within 300 s, reflecting a reduction of apparent viscosity. These time-dependent changes of flow behavior increased strongly with decreasing wall shear stress and with increasing tube diameter. A correlation between the width of the marginal plasma layer and relative apparent viscosity was obtained for every condition of tube diameter, wall shear stress, and time. Time-dependent changes of blood rheological properties could be relevant in the circulation, where the blood is exposed to rapid and repeated transitions from high-shear flow conditions in the arterial and capillary system to low-shear conditions in the venous system.

scholarly journals Endothelial cells express a unique transcriptional profile under very high wall shear stress known to induce expansive arterial remodeling

2012 ◽  
Vol 302 (8) ◽  
pp. C1109-C1118 ◽  
Author(s):  
Jennifer M. Dolan ◽  
Fraser J. Sim ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Gene Expression ◽  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Plasminogen Activator ◽  
Transcriptional Profile ◽  
Arterial Remodeling ◽  
Flow Conditions ◽  
Wall Shear ◽  
Very High

Chronic high flow can induce arterial remodeling, and this effect is mediated by endothelial cells (ECs) responding to wall shear stress (WSS). To assess how WSS above physiological normal levels affects ECs, we used DNA microarrays to profile EC gene expression under various flow conditions. Cultured bovine aortic ECs were exposed to no-flow (0 Pa), normal WSS (2 Pa), and very high WSS (10 Pa) for 24 h. Very high WSS induced a distinct expression profile compared with both no-flow and normal WSS. Gene ontology and biological pathway analysis revealed that high WSS modulated gene expression in ways that promote an anti-coagulant, anti-inflammatory, proliferative, and promatrix remodeling phenotype. A subset of characteristic genes was validated using quantitative polymerase chain reaction: very high WSS upregulated ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin motif-1), PLAU (urokinase plasminogen activator), PLAT (tissue plasminogen activator), and TIMP3, all of which are involved in extracellular matrix processing, with PLAT and PLAU also contributing to fibrinolysis. Downregulated genes included CXCL5 and IL-8 and the adhesive glycoprotein THBS1 (thrombospondin-1). Expressions of ADAMTS1 and uPA proteins were assessed by immunhistochemistry in rabbit basilar arteries experiencing increased flow after bilateral carotid artery ligation. Both proteins were significantly increased when WSS was elevated compared with sham control animals. Our results indicate that very high WSS elicits a unique transcriptional profile in ECs that favors particular cell functions and pathways that are important in vessel homeostasis under increased flow. In addition, we identify specific molecular targets that are likely to contribute to adaptive remodeling under elevated flow conditions.

A study of wall shear stress in 12 aneurysms with respect to different viscosity models and flow conditions

2013 ◽  
Vol 46 (16) ◽  
pp. 2802-2808 ◽  
Author(s):  
Øyvind Evju ◽  
Kristian Valen-Sendstad ◽  
Kent-André Mardal
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Conditions ◽  
Viscosity Models ◽  
Wall Shear

In vitro measurements of velocity and wall shear stress in a novel sequential anastomotic graft design model under pulsatile flow conditions

2014 ◽  
Vol 36 (10) ◽  
pp. 1233-1245 ◽  
Author(s):  
Foad Kabinejadian ◽  
Dhanjoo N. Ghista ◽  
Boyang Su ◽  
Mercedeh Kaabi Nezhadian ◽  
Leok Poh Chua ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pulsatile Flow ◽  
Design Model ◽  
Flow Conditions ◽  
In Vitro Measurements ◽  
Wall Shear

Disturbed Flow and Flow-Accelerated Corrosion in Oil and Gas Production

1998 ◽  
Vol 120 (1) ◽  
pp. 72-77 ◽  
Author(s):  
K. D. Efird
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Oil And Gas ◽  
Steel Corrosion ◽  
Flow Conditions ◽  
Accelerated Corrosion ◽  
Disturbed Flow ◽  
Wall Shear ◽  
Flow Accelerated Corrosion

The effect of fluid flow on corrosion of steel in oil and gas environments involves a complex interaction of physical and chemical parameters. The basic requirement for any corrosion to occur is the existence of liquid water contacting the pipe wall, which is primarily controlled by the flow regime. The effect of flow on corrosion, or flow-accelerated corrosion, is defined by the mass transfer and wall shear stress parameters existing in the water phase that contacts the pipe wall. While existing fluid flow equations for mass transfer and wall shear stress relate to equilibrium conditions, disturbed flow introduces nonequilibrium, steady-state conditions not addressed by these equations, and corrosion testing in equilibrium conditions cannot be effectively related to corrosion in disturbed flow. The problem in relating flow effects to corrosion is that steel corrosion failures in oil and gas environments are normally associated with disturbed flow conditions as a result of weld beads, pre-existing pits, bends, flanges, valves, tubing connections, etc. Steady-state mass transfer and wall shear stress relationships to steel corrosion and corrosion testing are required for their application to corrosion of steel under disturbed flow conditions. A procedure is described to relate the results of a corrosion test directly to corrosion in an operation system where disturbed flow conditions are expected, or must be considered.

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

1997 ◽  
Vol 119 (2) ◽  
pp. 187-194 ◽  
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.

scholarly journals Oxygen release from arterioles with normal flow and no-flow conditions

2006 ◽  
Vol 100 (5) ◽  
pp. 1569-1576 ◽  
Author(s):  
Pedro Cabrales ◽  
Amy G. Tsai ◽  
Paul C. Johnson ◽  
Marcos Intaglietta
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Oxygen Release ◽  
Flow Conditions ◽  
Phosphorescence Quenching ◽  
Dextran 70 ◽  
Lower Oxygen ◽  
Arteriolar Wall ◽  
Wall Shear

The rate of oxygen release from arterioles (∼55 μm diameter) was measured in the hamster window chamber model during flow and no-flow conditions. Flow was stopped by microvascular transcutaneous occlusion using a glass pipette held by a manipulator. The reduction of the intra-arteriolar oxygen tension (Po2) was measured by the phosphorescence quenching of preinfused Pd-porphyrin, 100 μm downstream from the occlusion. Oxygen release from arterioles was found to be 53% greater during flow than no-flow conditions (2.6 vs. 1.7 × 10−5 ml O2·cm−2·s−1, P < 0.05). Acute hemodilution with dextran 70 was used to reduce vessel oxygen content, significantly increase wall shear stress (14%, P < 0.05), reduce Hct to 28.4% (SD 1.0) [vs. 48.8% (SD 1.8) at baseline], lower oxygen supply by the arterioles (10%, P < 0.05), and increase oxygen release from the arterioles (39%, P < 0.05). Hemodilution also increased microcirculation oxygen extraction (33% greater than nonhemodilution, P < 0.05) and oxygen consumption by the vessel wall, as shown by an increase in vessel wall oxygen gradient [difference in Po2 between the blood and the tissue side of the arteriolar wall, nonhemodiluted 16.2 Torr (SD 1.0) vs. hemodiluted 18.3 Torr (SD 1.4), P < 0.05]. Oxygen released by the arterioles during flow vs. nonflow was increased significantly after hemodilution (3.6 vs. 1.8 × 10−5 ml O2·cm−2·s−1, P < 0.05). The oxygen cost induced by wall shear stress, suggested by our findings, may be >15% of the total oxygen delivery to tissues by arterioles during flow in this preparation.

Wall Shear Stress and Differential Pressure in Large-Diameter Horizontal Multiphase Pipelines

2000 ◽  
Vol 122 (4) ◽  
pp. 193-197 ◽  
Author(s):  
Lisa C. Maley ◽  
W. Paul Jepson
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Transducer ◽  
Large Diameter ◽  
Pressure Fluctuations ◽  
Differential Pressure ◽  
Bubble Collapse ◽  
Flow Conditions ◽  
Differential Pressure Transducer ◽  
Wall Shear

When a slug is formed a mixing vortex is created which contains pulses of bubbles which are shot toward the bottom of the pipe where they may impact and collapse. Bubble collapse creates high localized pressure, temperature, and wall shear stress, which cause a reduction in corrosion inhibitor efficiency. The average wall shear stress can be calculated using a conventional equation. However, using a conventional equation will not give the fluctuations in wall shear stress, which can be significant for slug flow conditions. Wall shear stress instruments are generally not accurate for fluids other than water, therefore, it would be beneficial to develop a relationship between the fluctuations in wall shear stress and the fluctuations in differential pressure. A differential pressure transducer, which can be used with any fluid, can be used to measure the fluctuations in differential pressure and then translate those values to fluctuations in wall shear stress. This study shows that wall shear stress fluctuations are related to differential pressure fluctuations to the 1.16 power. [S0195-0738(00)00604-X]

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