On quasi-steady laminar flow separation in the upper airways

2009 ◽  
Vol 25 (5) ◽  
pp. 447-461 ◽  
Author(s):  
A. Van Hirtum ◽  
J. Cisonni ◽  
X. Pelorson
Keyword(s):  
Laminar Flow ◽  
Flow Separation ◽  
Upper Airways ◽  
Steady Laminar

Wakes behind a prolate spheroid in crossflow

2012 ◽  
Vol 701 ◽  
pp. 98-136 ◽  
Author(s):  
George K. El Khoury ◽  
Helge I. Andersson ◽  
Bjørnar Pettersen
Keyword(s):  
Laminar Flow ◽  
Circular Cylinder ◽  
Flow Separation ◽  
Equatorial Plane ◽  
Major Axis ◽  
Prolate Spheroid ◽  
Transitional Flow ◽  
Meridional Plane ◽  
Axis Switching ◽  
Steady Laminar

AbstractViscous laminar flow past a prolate $(L/ d= 6)$ spheroid has been investigated numerically at seven different Reynolds numbers; $\mathit{Re}= 50, 75, 100, 150, 200, 250$ and $300$. In contrast to all earlier investigations, the major axis of the spheroid was oriented perpendicular to the free stream flow. As expected, the flow field in the wake showed a strong resemblance of that observed behind a finite-length circular cylinder, yet had features observed in the axisymmetric wake behind a sphere. The following different flow regimes were observed in the present computational study: (i) steady laminar flow with massive flow separation and symmetry about the equatorial and the meridional planes at $\mathit{Re}= 50$; (ii) steady laminar flow with massive flow separation and symmetry about the equatorial and the meridional plane at $\mathit{Re}= 75$, but the flow in the equatorial plane did no longer resemble the steady wake behind a circular cylinder; (iii) unsteady laminar flow with Strouhal number $0. 109$ and symmetry about the equatorial plane at $\mathit{Re}= 100$; (iv) unsteady laminar flow with two distinct frequencies and without any planar symmetries at $\mathit{Re}= 200$; (v) transitional flow with a dominant shedding frequency $\mathit{St}= 0. 151$ and without any spatial symmetries at $\mathit{Re}= 300$. For all but the two lowest $\mathit{Re}$ hairpin vortices were alternately shed from the two sides of the spheroid and resulted in a ladder-like pattern of oppositely oriented vortex structures, in contrast with the single-sided shedding in the wake of a sphere. The contour of the very-near-wake mimicked the shape of the prolate spheroid. However, $15d$ downstream the major axis of the wake became aligned with the minor axis of the spheroid. This implies that an axis switching occurred some $10d$ downstream, i.e. the cross-section of the wake evolved such that the major and minor axes interchanged at a certain downstream location. This peculiar phenomenon has frequently been reported to arise for elliptical and rectangular jets, whereas observations of axis switching for asymmetric wakes are scarce.

scholarly journals Anomalous mobility of a driven active particle in a steady laminar flow

2018 ◽  
Vol 30 (26) ◽  
pp. 264002 ◽  
Author(s):  
F Cecconi ◽  
A Puglisi ◽  
A Sarracino ◽  
A Vulpiani
Keyword(s):  
Laminar Flow ◽  
Active Particle ◽  
Steady Laminar

Steady Laminar Flow through Twisted Pipes: Fluid Flow in Square Tubes

1981 ◽  
Vol 103 (4) ◽  
pp. 785-790 ◽  
Author(s):  
J. H. Masliyah ◽  
K. Nandakumar
Keyword(s):  
Laminar Flow ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Dissipation Term ◽  
Axial Velocity Profile ◽  
Secondary Motion ◽  
Qualitative Nature ◽  
Flow Through ◽  
Steady Laminar

The Navier-Stokes equation in a rotating frame of reference is solved numerically to obtain the flow field for a steady, fully developed laminar flow of a Newtonian fluid in a twisted tube having a square cross-section. The macroscopic force and energy balance equations and the viscous dissipation term are presented in terms of variables in a rotating reference frame. The computed values of friction factor are presented for dimensionless twist ratios, (i.e., length of tube over a rotation of π radians normalized with respect to half the width of tube) of 20, 10, 5 and 2.5 and for Reynolds numbers up to 2000. The qualitative nature of the axial velocity profile was observed to be unaffected by the swirling motion. The secondary motion was found to be most important near the wall.

Laminar Flow on Endothelial Cells Suppresses eNOS O-GlcNAcylation to Promote eNOS Activity

2021 ◽  
Author(s):  
Sarah Basehore ◽  
Samantha Bohlman ◽  
Callie Weber ◽  
Swathi Swaminathan ◽  
Yuji Zhang ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Endothelial Cells ◽  
Shear Stress ◽  
Laminar Flow ◽  
No Production ◽  
Disturbed Flow ◽  
Enos Activity ◽  
Enos Phosphorylation ◽  
Steady Laminar ◽  
In Cells

Rationale: In diabetic animals as well as high glucose cell culture conditions, endothelial nitric oxide synthase (eNOS) is heavily O-GlcNAcylated, which inhibits its phosphorylation and nitric oxide (NO) production. It is unknown, however, whether varied blood flow conditions, which affect eNOS phosphorylation, modulate eNOS activity via O-GlcNAcylation-dependent mechanisms. Objective: The goal of this study was to test if steady laminar flow, but not oscillating disturbed flow, decreases eNOS O-GlcNAcylation, thereby elevating eNOS phosphorylation and NO production. Methods and Results: Human umbilical vein endothelial cells (HUVEC) were exposed to either laminar flow (20 dynes/cm2 shear stress) or oscillating disturbed flow (4{plus minus}6 dynes/cm2 shear stress) for 24 hours in a cone-and-plate device. eNOS O-GlcNAcylation was almost completely abolished in cells exposed to steady laminar but not oscillating disturbed flow. Interestingly, there was no change in protein level or activity of key O-GlcNAcylation enzymes (OGT, OGA, or GFAT). Instead, metabolomics data suggest that steady laminar flow decreases glycolysis and hexosamine biosynthetic pathway (HBP) activity, thereby reducing UDP-GlcNAc pool size and consequent O-GlcNAcylation. Inhibition of glycolysis via 2-deoxy-2-glucose (2-DG) in cells exposed to disturbed flow efficiently decreased eNOS O-GlcNAcylation, thereby increasing eNOS phosphorylation and NO production. Finally, we detected significantly higher O-GlcNAcylated proteins in endothelium of the inner aortic arch in mice, suggesting that disturbed flow increases protein O-GlcNAcylation in vivo. Conclusions: Our data demonstrate that steady laminar but not oscillating disturbed flow decreases eNOS O-GlcNAcylation by limiting glycolysis and UDP-GlcNAc substrate availability, thus enhancing eNOS phosphorylation and NO production. This research shows for the first time that O-GlcNAcylation is regulated by mechanical stimuli, relates flow-induced glycolytic reductions to macrovascular disease, and highlights targeting HBP metabolic enzymes in endothelial cells as a novel therapeutic strategy to restore eNOS activity and prevent EC dysfunction in cardiovascular disease.

Converting steady laminar flow to oscillatory flow through a hydroelasticity approach at microscales

Lab on a Chip ◽  
2012 ◽  
Vol 12 (1) ◽  
pp. 60-64 ◽  
Author(s):  
H. M. Xia ◽  
Z. P. Wang ◽  
W. Fan ◽  
A. Wijaya ◽  
W. Wang ◽  
...  
Keyword(s):  
Laminar Flow ◽  
Oscillatory Flow ◽  
Flow Through ◽  
Steady Laminar
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