Grid resolution requirement for resolving rare and high intensity wall-shear stress events in direct numerical simulations

2021 ◽  
Vol 6 (5) ◽  
Author(s):  
Xiang I. A. Yang ◽  
Jiarong Hong ◽  
Myoungkyu Lee ◽  
Xinyi L. D. Huang
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
High Intensity ◽  
Direct Numerical Simulations ◽  
Grid Resolution ◽  
Wall Shear

Direct numerical simulations of turbulent flows over superhydrophobic surfaces

2009 ◽  
Vol 620 ◽  
pp. 31-41 ◽  
Author(s):  
MICHAEL B. MARTELL ◽  
J. BLAIR PEROT ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Slip Velocity ◽  
Direct Numerical Simulations ◽  
Superhydrophobic Surfaces ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Wall Shear

Direct numerical simulations (DNSs) are used to investigate the drag-reducing performance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air–water interface. Slip velocities, wall shear stresses and Reynolds stresses are considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of Reτ ≈ 180. For the largest microfeature spacing studied, an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is found to be nearly 40%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress but is offset by a slip velocity that increases with increasing microfeature spacing.

scholarly journals Acute Stent-Induced Endothelial Denudation: Biomechanical Predictors of Vascular Injury

2021 ◽  
Vol 8 ◽  
Author(s):  
Claire Conway ◽  
Farhad R. Nezami ◽  
Campbell Rogers ◽  
Adam Groothuis ◽  
James C. Squire ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Vascular Injury ◽  
Ex Vivo ◽  
Circumferential Stress ◽  
Arterial Injury ◽  
Stent Design ◽  
Endothelial Denudation ◽  
Wall Shear

Recent concern for local drug delivery and withdrawal of the first Food and Drug Administration-approved bioresorbable scaffold emphasizes the need to optimize the relationships between stent design and drug release with imposed arterial injury and observed pharmacodynamics. In this study, we examine the hypothesis that vascular injury is predictable from stent design and that the expanding force of stent deployment results in increased circumferential stress in the arterial tissue, which may explain acute injury poststent deployment. Using both numerical simulations and ex vivo experiments on three different stent designs (slotted tube, corrugated ring, and delta wing), arterial injury due to device deployment was examined. Furthermore, using numerical simulations, the consequence of changing stent strut radial thickness on arterial wall shear stress and arterial circumferential stress distributions was examined. Regions with predicted arterial circumferential stress exceeding a threshold of 49.5 kPa compared favorably with observed ex vivo endothelial denudation for the three considered stent designs. In addition, increasing strut thickness was predicted to result in more areas of denudation and larger areas exposed to low wall shear stress. We conclude that the acute arterial injury, observed immediately following stent expansion, is caused by high circumferential hoop stresses in the interstrut region, and denuded area profiles are dependent on unit cell geometric features. Such findings when coupled with where drugs move might explain the drug–device interactions.

Steady Flow in an Aneurysm Model: Correlation Between Fluid Dynamics and Blood Platelet Deposition

1996 ◽  
Vol 118 (3) ◽  
pp. 280-286 ◽  
Author(s):  
D. Bluestein ◽  
L. Niu ◽  
R. T. Schoephoerster ◽  
M. K. Dewanjee
Keyword(s):  
Fluid Dynamics ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Recirculation Zone ◽  
Blood Platelet ◽  
Platelet Deposition ◽  
Order Of Magnitude ◽  
Wall Shear ◽  
Aneurysm Model

Laminar and turbulent numerical simulations of steady flow in an aneurysm model were carried out over Reynolds numbers ranging from 300 to 3600. The numerical simulations are validated with Digital Particle Image Velocimetry (DPIV) measurements, and used to study the fluid dynamic mechanisms that characterize aneurysm deterioration, by correlating them to in vitro blood platelet deposition results. It is shown that the recirculation zone formed inside the aneurysm cavity creates conditions that promote thrombus formation and the viability of rupture. Wall shear stress values in the recirculation zone are around one order of magnitude less than in the entrance zone. The point of reattachment at the distal end of the aneurysm is characterized by a pronounced wall shear stress peak. As the Reynolds number increases in laminar flow, the center of the recirculation region migrates toward the distal end of the aneurysm, increasing the pressure at the reattachment point. Under fully turbulent flow conditions (Re = 3600) the recirculation zone inside the aneurysm shrinks considerably. The wall shear stress values are almost one order of magnitude larger than those for the laminar cases. The fluid dynamics mechanisms inferred from the numerical simulation were correlated with measurements of blood platelet deposition, offering useful explanations for the different morphologies of the platelet deposition curves.

Numerical simulations of maternal blood flows in the human placenta: estimation of the wall shear stress exerted on the syncytiotrophoblast

Placenta ◽  
2014 ◽  
Vol 35 (9) ◽  
pp. A105
Author(s):  
Edouard Lecarpentier ◽  
Mrugank Bhatt ◽  
Thierry Fournier ◽  
Abdul Barakat ◽  
Vassilis Tsatsaris
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Human Placenta ◽  
Maternal Blood ◽  
Blood Flows ◽  
Wall Shear

scholarly journals Low- and High-Drag Intermittencies in Turbulent Channel Flows

Entropy ◽  
2020 ◽  
Vol 22 (10) ◽  
pp. 1126 ◽  
Author(s):  
Rishav Agrawal ◽  
Henry C.-H. Ng ◽  
Ethan A. Davis ◽  
Jae Sung Park ◽  
Michael D. Graham ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Reynolds Shear Stress ◽  
Frequency Of Occurrence ◽  
Time Duration ◽  
Wall Shear ◽  
Conditional Events ◽  
Duration Criterion

Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low- and high-drag events in Newtonian fluid flows, at Reτ=uτh/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed “hibernating” and “hyperactive”, respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk’s maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.

A Numerical Simulation of Flow in a Two-Dimensional End-to-Side Anastomosis Model

1993 ◽  
Vol 115 (1) ◽  
pp. 112-118 ◽  
Author(s):  
D. A. Steinman ◽  
Bach Vinh ◽  
C. Ross Ethier ◽  
M. Ojha ◽  
R. S. C. Cobbold ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Intimal Hyperplasia ◽  
Cardiac Cycle ◽  
Numerical Code ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Spatial Gradients ◽  
Wall Shear

In order to understand the possible role that hemodynamic factors may play in the pathogenesis of distal anastomotic intimal hyperplasia, we carried out numerical simulations of the flow field within a two-dimensional 45 degree rigid-walled end-to-side model anastomosis. The numerical code was tested and compared with experimental (photochromic dye tracer) studies using steady and near-sinusoidal waveforms, and agreement was generally very good. Using a normal human superficial femoral artery waveform, numerical simulations indicated elevated instantaneous wall shear stress magnitudes at the toe and heel of the graft-host junction and along the host artery bed. These sites also experienced highly variable wall shear stress behavior over the cardiac cycle, as well as elevated spatial gradients of wall shear stress. These observations provide additional evidence that intimal hyperplasia may be correlated to wall shear stresses over the cardiac cycle, high wall shear stress gradients, or a combination of the three. The limitations of the present work (especially in regard to the two-dimensional nature of the flow simulations) are discussed, and results are compared to previous observations about distal anastomotic intimal hyperplasia.

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