The Role of Pressure-Velocity Correlation in Oscillatory Flow Between a Pair of Bluff Bodies

2005 ◽  
pp. 481-490
Author(s):  
Shinnosuke Obi ◽  
Norihiko Tokai ◽  
Keita Sakai
Keyword(s):  
Oscillatory Flow ◽  
Bluff Bodies ◽  
Velocity Correlation

Discovery of Side- and Shear-Dependent miRNAs and mRNAs in Human Aortic Valvular Endothelial Cells

2011 ◽  
Author(s):  
Casey J. Holliday ◽  
Randall F. Ankeny ◽  
Hanjoong Jo ◽  
Robert M. Nerem
Keyword(s):  
Endothelial Cells ◽  
Aortic Valve ◽  
Oscillatory Flow ◽  
Expression Profiles ◽  
Flow Conditions ◽  
Expression Of Genes ◽  
Inflammatory Phenotype ◽  
Cardiovascular Pathologies ◽  
Laminar Shear

Aortic valve (AV) disease is diagnosed by severe symptoms, such as calcification, and typically treated by AV replacement and repair surgeries. The mechanism by which AV disease occurs, specifically the role of the endothelium remains relatively unknown. It is known that disease preferentially occurs on the fibrosa, or aortic side, where it is exposed to disturbed, oscillatory flow, whereas the ventricularis, or side facing the left ventricle, experiences pulsatile, laminar shear and remains non-calcified [1, 2]. Research shows that regulation of miRNAs, short nucleotide segments targeting mRNAs, coincides with cardiovascular pathologies [3] though expression profiles of miRNAs and the mRNAs they modulate in human AV endothelial cells (HAVECs) have not been reported. We hypothesize that disturbed flow conditions present on the fibrosa stimulate ECs to modify expression of genes and miRNAs to induce a pro-inflammatory phenotype.

scholarly journals A Lagrangian-Based Approach for Determining Trajectories Taxonomy and Turbulence Regimes

2007 ◽  
Vol 37 (6) ◽  
pp. 1584-1609 ◽  
Author(s):  
Volfango Rupolo
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Eddy Diffusivity ◽  
General Circulation Models ◽  
Velocity Correlation ◽  
Velocity Correlation Function ◽  
Different Shapes ◽  
Surface Drifters ◽  
Current Systems

Abstract The use of the ratio between the acceleration and velocity time scales y = Ta/Tυ to separate Lagrangian trajectories in homogeneous classes is proposed. In fact, when analyzing subsurface floats data in the Atlantic Ocean and surface drifters data in the world’s ocean basins, it is observed that trajectories having different values of y are characterized by different shapes, correlation, and dispersal properties. In particular, trajectories having similar values of the acceleration and velocity time scales clearly show the influence of eddies and are characterized by an oscillating velocity correlation function. It is shown here that this trajectory screening is a useful procedure to rationalize the analysis of real Lagrangian trajectories and to avoid a mixture of different regimes, when averaging quantities. The mean statistical quantities computed averaging on quasi-homogeneous datasets put in evidence the role of the coherent structures in the dispersion properties, both in time and in the main oceanic current systems. These results are discussed in the context of the parameterization of eddy diffusivity in general circulation models.

Vortex shedding from bluff bodies in oscillatory flow: A report on Euromech 119

1980 ◽  
Vol 99 (2) ◽  
pp. 225-245 ◽  
Author(s):  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Bluff Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Unidirectional Flow ◽  
Low Reynolds Number Flows ◽  
Wide Range ◽  
Bluff Body Flow ◽  
Reynolds Number Flows

European Mechanics Colloquium number 119 was held at Imperial College on 16–18 July 1979, when the subject of vortex shedding from bodies in unidirectional flow and oscillatory flow, was discussed. A wide range of experimental work was presented including low-Reynolds-number flows around circular cylinders, the influence of disturbances on bluff body flow, the measurement of fluctuating forces and the influence of oscillations of the stream. About a third of the 33 papers presented concentrated on theoretical aspects and the majority of these were concerned with the ‘method of discrete vortices’.

On Flame Stabilization by Bluff-Bodies

1980 ◽  
Vol 102 (1) ◽  
pp. 209-214 ◽  
Author(s):  
K. M. Kundu ◽  
D. Banerjee ◽  
D. Bhaduri
Keyword(s):  
Heat Exchange ◽  
Recirculation Zone ◽  
Flame Stabilization ◽  
Flame Stability ◽  
Bluff Bodies

Flame stabilization by bluff-bodies has been investigated to highlight the role of recirculation zone on the phenomenon. It has been observed that close correlations exist between heat exchange from recirculation zone and flame stability as controlled by recirculation strength.

On the Role of Correlation Between Instantaneous Velocity and Pressure-Gradient in Large-Scale Turbulence

2003 ◽  
Author(s):  
Shinnosuke Obi
Keyword(s):  
Pressure Gradient ◽  
Reynolds Stress ◽  
Large Scale ◽  
Stress Component ◽  
Turbulent Transport ◽  
Velocity Correlation ◽  
Gradient Diffusion ◽  
Scale Turbulence ◽  
The Individual

Turbulent transport of Reynolds stress by triple moment of fluctuating velocity and pressure-velocity correlation are evaluated from a DNS for wake of a rectangular cylinder located in a uniform flow. The turbulent diffusion transport of turbulent kinetic energy hardly correlates with its gradient vector, indicating that the generally accepted gradient diffusion model is inadequate. It is inferred that the separate modeling of the individual Reynolds stress component provides a better possibility for modeling the turbulent transport in this flow, because of the strong departure from the equilibrium state of turbulence. The possibility of the direct modeling of the pressure gradient-velocity correlation is discussed.

scholarly journals Chemokines and Growth Factors Produced by Lymphocytes in the Incompetent Great Saphenous Vein

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Ewa Grudzińska ◽  
Sławomir Grzegorczyn ◽  
Zenon P. Czuba
Keyword(s):  
Growth Factors ◽  
Growth Factor ◽  
Saphenous Vein ◽  
Oscillatory Flow ◽  
Great Saphenous Vein ◽  
Upper Limbs ◽  
Colony Stimulating Factor ◽  
Gm Csf ◽  
Stimulating Factor

The role of cytokines in the pathogenesis of chronic venous disease (CVD) remains obscure. It has been postulated that oscillatory flow present in incompetent veins causes proinflammatory changes. Our earlier study confirmed this hypothesis. This study is aimed at assessing chemokines and growth factors (GFs) released by lymphocytes in patients with great saphenous vein (GSV) incompetence. In 34 patients exhibiting reflux in GSV, blood was derived from the cubital vein and from the incompetent saphenofemoral junction. In 12 healthy controls, blood was derived from the cubital vein. Lymphocyte culture with and without stimulation by phytohemagglutinin (PHA) was performed. Eotaxin, interleukin 8 (IL-8), macrophage inflammatory protein 1 A and 1B (MIP-1A and MIP-1B), interferon gamma-induced protein (IP-10), monocyte chemoattractant protein-1 (MCP-1), interleukin 5 (IL-5), fibroblast growth factor (FGF), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), platelet-derived growth factor-BB (PDGF-BB), and vascular endothelial growth factor (VEGF) were assessed in culture supernatants by a Bio-Plex assay. Higher concentrations of eotaxin and G-CSF were revealed in the incompetent GSV, compared with the concentrations in the patients’ upper limbs. The concentrations of MIP-1A and MIP-1B were higher in the CVD group while the concentration of VEGF was lower. In the stimulated cultures, the concentration of G-CSF proved higher in the incompetent GSV, as compared with the patients’ upper limbs. Between the groups, the concentration of eotaxin was higher in the CVD group, while the IL-5 and MCP-1 concentrations were lower. IL-8, IP-10, FGF, GM-CSF, and PDGF-BB did not reveal any significant differences in concentrations between the samples. These observations suggest that the concentrations of chemokines and GFs are different in the blood of CVD patients. The oscillatory flow present in incompetent veins may play a role in these changes. However, the role of cytokines in CVD requires further study.

scholarly journals On the recirculating flow of three-dimensional asymmetric bluff bodies

2020 ◽  
Vol 61 (12) ◽  
Author(s):  
Antoine Legeai ◽  
Olivier Cadot
Keyword(s):  
Bluff Body ◽  
Reference Model ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Recirculating Flow ◽  
Bistable Dynamics ◽  
Geometrical Variation ◽  
Static Instability ◽  
State Selection

Abstract The paper investigates the role of geometrical asymmetric modifications of a rectangular flat-backed body on the properties of the recirculating flow at a Reynolds number $$Re=1.8\times 10^5$$ R e = 1.8 × 10 5 . The reference model has two reflectional symmetries denoted $$s_y$$ s y and $$s_z$$ s z in both spanwise directions. The flow is subjected to the static instability that leads to two mirrored wake states breaking the symmetry $$s_y$$ s y . Two families of geometrical variation of the fore-body and after-body are studied, each breaking one of the reflectional symmetries of the reference model. Geometrical modifications that preserve $$s_y$$ s y evidence possibilities of bistable dynamics suppression although the static instability persists. Geometrical modifications that do not preserve $$s_y$$ s y produces a large unbalance of both wake states in accordance to recent observations on real cars (Bonnavion et al. in J Wind Eng Ind Aerodyn 184:77–89, 2019). Results offer perspectives for potential drag reduction induced by appropriate coupling of bluff body geometry and wake state selection. Graphic abstract

Abstract 570: Cystathionine γ-Lyase Modulates Flow-dependent Vascular Remodeling

2016 ◽  
Vol 36 (suppl_1) ◽  
Author(s):  
Shuai Yuan ◽  
Arif Yurdagul ◽  
Jonette M Green ◽  
Sibile Pardue ◽  
Christopher G Kevil ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Vascular Remodeling ◽  
Oscillatory Flow ◽  
Carotid Arteries ◽  
Dependent Manner ◽  
Disturbed Flow ◽  
Sulfane Sulfur ◽  
Nitrite Level

Disturbed flow causes endothelial dysfunction and development of atherosclerotic lesions. The gaseous signaling molecule H 2 S and cystathionine γ-lyase (CSE), its major enzymatic source in the vasculature, protect against cardiovascular diseases including atherosclerosis, peripheral artery disease, and cardiac ischemia in a nitric oxide (NO) dependent manner. Therefore, we sought to investigate the role of CSE in the endothelial response to disturbed flow. Wild-type C57Bl/6 (WT) and CSE knockout (CSE-/-) mice underwent partial carotid ligation to induce disturbed flow in the left carotid with the right carotid serving as an internal control. Additionally, endothelial cells isolated from WT and CSE-/- mice were exposed to oscillatory flow, a model of disturbed flow, in vitro. While disturbed flow decreased endothelial CSE mRNA expression, CSE protein expression showed strong induction under disturbed flow conditions both in vitro and in vivo. This induction correlated with enhanced free sulfide and sulfane sulfur production in WT but not in CSE-/- mice. Intimal mRNA isolated 2 days post-ligation showed increased VCAM-1 and ICAM-1 expression in WT mice which was prevented in CSE-/- mice. Similarly, endothelial cells isolated from CSE-/- mice show reduced NF-B activation and proinflammatory gene expression in response to oscillatory flow in vitro. Morphometric analysis of carotid arteries collected 7 days post-ligation revealed reduced macrophage infiltration and medial thickening in the ligated carotid of CSE-/- mice. Interestingly, ligation increased the carotid nitrite level in WT mice but not in CSE-/- mice. However, nitrite level of the non-ligated carotid was significantly higher in the CSE-/- mice compared to WT mice. Shear induced phosphorylation of eNOS Ser1179 in vitro was not different between WT and CSE knockout endothelial cells, suggesting alternative regulatory mechanisms. Collectively, CSE in mouse carotid arteries plays a critical role in flow dependent vascular remodeling, which may be mediated by CSE derived free sulfide and sulfane sulfur. CSE deficiency completely inhibits disturbed flow-induced NF-κB activation and macrophage recruitment, consistent with the role of inflammation in vascular remodeling.

Role of Slip Velocity on the Oscillatory Flow of Blood Through a Porous Vessel in the Presence of Heat Source and Chemical Reaction

2014 ◽  
Vol 30 (2) ◽  
pp. 209-218 ◽  
Author(s):  
A. Sinha ◽  
G. C. Shit
Keyword(s):  
Magnetic Field ◽  
Chemical Reaction ◽  
Slip Velocity ◽  
Oscillatory Flow ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Suction Velocity ◽  
Heat Generation Or Absorption ◽  
Nicolson Scheme

ABSTRACTOf concern in this paper is a problem motivated towards studying the influence of slip velocity on heat and mass transfer in the unsteady flow of blood through a porous vessel, when the lumen of the vessel has turned into a porous structure with internal heat generation or absorption in the presence of chemical reaction. It is assumed that the influence of a uniform magnetic field acts normal to the flow and the permeability of the porous medium fluctuates with time. The suction velocity is also taken to be oscillates periodically. The problem is solved numerically by using Crank-Nicolson scheme. The computational results are presented graphically for the velocity, temperature and concentration distribution as well as the variation of skin-friction co-efficient, Nusselt number and Sherwood number for various values of the parameters involved in this analysis. The study reveals that the flow is appreciably influenced by the presence of a magnetic field and slip velocity.

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