scholarly journals NUMERICAL EVALUATION OF CURVATURE EFFECTS ON SHEAR STRESSES ACROSS ARTERIAL STENOSES

2002 ◽  
Vol 14 (04) ◽  
pp. 164-170 ◽  
Author(s):  
YANG-YAO NIU ◽  
WEI-KUANG CHU ◽  
LUNG-CHENG LEE ◽  
HSI-YU YU
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Arterial Walls ◽  
Curvature Effects ◽  
Newtonian Flows ◽  
Flow Features ◽  
Wall Shear ◽  
Arterial Stenoses

In this study, Newtonian flows passing through three-dimensional curved and straight axissymmetrical stenotic tubes are investigated. The geometry effects and Reynolds numbers of 100, 200, 400, and 600 on the formation of the shear rate over arterial walls are studied. It is noted that geometric effects on flow features such as velocity profiles, pressure and wall shear stress distributions in the post-stenotic region are significant. The location of maximum wall shear stress is found to relate to the geometric effect much than the Reynolds number effect.

3D CFD Simulation of Water Hammer Through a 90° Bend: Applicability of URANS, 3D Effects and Unsteady Friction

2014 ◽  
Author(s):  
Stefan Riedelmeier ◽  
Stefan Becker ◽  
Eberhard Schlücker
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Water Hammer ◽  
Dynamics Simulation ◽  
Shear Stresses ◽  
Velocity Gradients ◽  
Wall Shear ◽  
The Impact

In most cases, the method of characteristics is used to calculate the propagation of water hammer in hydraulic systems due to the size of those pipings, although three-dimensional effects are known to occur. In order to investigate and quantify these effects, a three-dimensional computational fluid dynamics simulation of water hammer through a bend geometry was performed. For the resolution of the developing high spatial and temporal gradients an adequate mesh and suitable physical model was generated using a commercial code. The applicability of unsteady Reynolds-averaged Navier-Stokes simulation was evaluated considering the turbulent properties of the flow using results from the literature. Furthermore velocity, pressure, wall shear stress and vorticity distributions are presented. The effect of the 90° bend as three-dimensional element was identified and the impact on the flow field is presented. In the end, the annular effect is discussed. Due to the high forces of inertia in the boundary layer and the dominating viscous forces close to the wall, high velocity gradients are developing resulting in high wall shear stresses. It is shown that the viscous and turbulent transport of momentum in the radial direction reduces these velocity gradients and limits the maximum occurring wall shear stress.

scholarly journals Bicuspid Aortic Cusp Fusion Morphology Alters Aortic Three-Dimensional Outflow Patterns, Wall Shear Stress, and Expression of Aortopathy

Circulation ◽  
2014 ◽  
Vol 129 (6) ◽  
pp. 673-682 ◽  
Author(s):  
Riti Mahadevia ◽  
Alex J. Barker ◽  
Susanne Schnell ◽  
Pegah Entezari ◽  
Preeti Kansal ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Aortic Cusp ◽  
Wall Shear

Preston-Static Tubes for the Measurement of Wall Shear Stress

1994 ◽  
Vol 116 (3) ◽  
pp. 645-649 ◽  
Author(s):  
Josef Daniel Ackerman ◽  
Louis Wong ◽  
C. Ross Ethier ◽  
D. Grant Allen ◽  
Jan K. Spelt
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Convenient Method ◽  
Pipe Flow ◽  
Total Pressure ◽  
Static Pressure ◽  
Shear Stresses ◽  
Streamline Curvature ◽  
Syringe Needle ◽  
Wall Shear

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Requirements for Mesh Resolution in 3D Computational Hemodynamics

2000 ◽  
Vol 123 (2) ◽  
pp. 134-144 ◽  
Author(s):  
Sujata Prakash ◽  
C. Ross Ethier
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Velocity Fields ◽  
Shear Stresses ◽  
Large Artery ◽  
Mesh Independence ◽  
Wall Shear

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features. Here we examine, for a single arterial geometry, how velocity and wall shear stress patterns depend on mesh characteristics. A well-validated Navier-Stokes solver was used to simulate flow in an anatomically realistic human right coronary artery (RCA) using unstructured high-order tetrahedral finite element meshes. Velocities, wall shear stresses (WSS), and wall shear stress gradients were computed on a conventional “high-resolution” mesh series (60,000 to 160,000 velocity nodes) generated with a commercial meshing package. Similar calculations were then performed in a series of meshes generated through an adaptive mesh refinement (AMR) methodology. Mesh-independent velocity fields were not very difficult to obtain for both the conventional and adaptive mesh series. However, wall shear stress fields, and, in particular, wall shear stress gradient fields, were much more difficult to accurately resolve. The conventional (nonadaptive) mesh series did not show a consistent trend towards mesh-independence of WSS results. For the adaptive series, it required approximately 190,000 velocity nodes to reach an r.m.s. error in normalized WSS of less than 10 percent. Achieving mesh-independence in computed WSS fields requires a surprisingly large number of nodes, and is best approached through a systematic solution-adaptive mesh refinement technique. Calculations of WSS, and particularly WSS gradients, show appreciable errors even on meshes that appear to produce mesh-independent velocity fields.

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.

scholarly journals Numerical Simulation of Dispersed Particle-Blood Flow in the Stenosed Coronary Arteries

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Mongkol Kaewbumrung ◽  
Somsak Orankitjaroen ◽  
Pichit Boonkrong ◽  
Buraskorn Nuntadilok ◽  
Benchawan Wiwatanapataphee
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Shear Stress ◽  
Coronary Artery ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Stokes Equations ◽  
Spherical Shape ◽  
Shear Stresses ◽  
Wall Shear

A mathematical model of dispersed bioparticle-blood flow through the stenosed coronary artery under the pulsatile boundary conditions is proposed. Blood is assumed to be an incompressible non-Newtonian fluid and its flow is considered as turbulence described by the Reynolds-averaged Navier-Stokes equations. Bioparticles are assumed to be spherical shape with the same density as blood, and their translation and rotational motions are governed by Newtonian equations. Impact of particle movement on the blood velocity, the pressure distribution, and the wall shear stress distribution in three different severity degrees of stenosis including 25%, 50%, and 75% are investigated through the numerical simulation using ANSYS 18.2. Increasing degree of stenosis severity results in higher values of the pressure drop and wall shear stresses. The higher level of bioparticle motion directly varies with the pressure drop and wall shear stress. The area of coronary artery with higher density of bioparticles also presents the higher wall shear stress.

Inflammatory Response of Endothelial Cells to Wall Shear Stress in Three Dimensional Stenotic Models

2009 ◽  
Author(s):  
Leonie Rouleau ◽  
Joanna Rossi ◽  
Jean-Claude Tardif ◽  
Rosaire Mongrain ◽  
Richard L. Leask
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Realistic Model ◽  
In Vitro Models ◽  
Steady Flows ◽  
Wall Shear

Endothelial cells (ECs) are believed to respond differentially to hemodynamic forces in the vascular tree. Once atherosclerotic plaque has formed in a vessel, the obstruction creates complex spatial gradients in wall shear stress (WSS). In vitro models have used mostly unrealistic and simplified geometries, which cannot reproduce accurately physiological conditions. The objective of this study was to expose ECs to the complex WSS pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flows in straight dynamic controls and in idealized asymmetric stenosis models. Cell morphology was noticeably different in the regions with spatial WSS gradients, being more randomly oriented and of cobblestone shape. Inflammatory molecule expression was also altered by exposure to shear and endothelial nitric oxide synthase (eNOS) was upregulated by its presence. A regional response in terms of inflammation was observed through confocal microscopy. This work provides a more realistic model to study endothelial cell response to spatial and temporal WSS gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.

Radial Stagnation Flow on a Twisting Cylinder

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Patrick Weidman
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shooting Method ◽  
Azimuthal Velocity ◽  
Shear Stresses ◽  
Torsional Motion ◽  
Stagnation Flow ◽  
Strong Function ◽  
Stress Parameter ◽  
Wall Shear

The problem of stagnation-point flow impinging radially on a linearly twisting cylinder is considered. This advances previous work on the motion outside a cylinder undergoing linear torsional motion. The problem is governed by a Reynolds number R and a dimensionless torsion rate σ. Numerical calculations are carried out using the ODEINT program, and convergence of the shooting method is obtained using the MNEWT program. The radial and azimuthal wall shear stresses are found over a range of R and σ, and radial and azimuthal velocity profiles at σ={0,1,2} are presented for various values of R. The interesting feature is that the axial wall shear stress parameter f″(1) is a very weak function of σ while the azimuthal wall shear stress parameter g′(1) is a strong function of σ although both stress parameters are a strong function of R.

Three-dimensional vortical structures and wall shear stress in a curved artery model

2019 ◽  
Vol 31 (12) ◽  
pp. 121903 ◽  
Author(s):  
Christopher Cox ◽  
Mohammad Reza Najjari ◽  
Michael W. Plesniak
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Vortical Structures ◽  
Curved Artery ◽  
Wall Shear
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