Flow Measurements in a Human Femoral Artery Model With Reverse Lumen Curvature

1988 ◽  
Vol 110 (4) ◽  
pp. 300-309 ◽  
Author(s):  
L. H. Back ◽  
M. R. Back ◽  
E. Y. Kwack ◽  
D. W. Crawford
Keyword(s):  
Steady Flow ◽  
Femoral Artery ◽  
Flow Simulation ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Reverse Direction ◽  
Flow Measurements ◽  
Left Femoral Artery ◽  
Lesion Localization ◽  
Made In

Flow visualization and wall pressure measurements were made in a smooth reverse curvature model that conformed to the gentle “s” shape of a left femoral artery angiogram of a patient in a clinical trial. Observed lesion localization at the inner (lesser) curvatures appeared to be associated with secondary flows in the wall vicinity directed toward the inner curvatures that tended to reverse direction in the flow entering the reverse curvature region. Moderate flow resistance increases of about 20 percent above the Poiseuille flow relation were found at the higher physiological Reynolds numbers Re above about 600–700 and thus Dean numbers for steady flow. For pulsatile flow simulation, flow resistances did not increase up to the largest Re of 470 tested. Apparently, the large variations in velocity during the cardiac cycle disrupted the stronger secondary flow patterns observed at the higher Reynolds numbers for steady flow.

Flow Measurements in an Atherosclerotic Curved, Tapered Femoral Artery Model of Man

1988 ◽  
Vol 110 (4) ◽  
pp. 310-319 ◽  
Author(s):  
L. H. Back ◽  
E. Y. Kwack ◽  
D. W. Crawford
Keyword(s):  
Flow Simulation ◽  
Reynolds Numbers ◽  
Flow Measurements ◽  
Pressure Drops ◽  
Physiological Conditions ◽  
Curvature Effects ◽  
Smooth Model ◽  
Lesion Localization ◽  
Flow Resistances

Flow visualization and pressure measurements were made for physiological conditions in a model derived from a femoral angiorgram of a patient with lesion localization on the inner curvature wall and with vessel taper. Effects of curvature and taper were evaluated separately in other curved, tapered, smooth and straight, tapered, smooth models. Double helical secondary flow patterns were modified by plaque on the inner wall, and flow separations were observed between plaques at higher flow rates and Reynolds numbers. Pressure drop data for the plaque simulation model were similar in trend with Reynolds number as for the smooth model, but flow resistances were 25 to 40 percent higher. Significant pressure drops were measured due to the mild taper which could be estimated from momentum considerations, and smaller increased pressure drops were found due to curvature effects at the higher Dean numbers. Flow resistances for in vivo pulsatile flow simulation were about 10 percent higher than for steady flow for the plaque model, whereas no differences were observed for the smooth model.

A Quasi-Unsteady Study on Wake Interaction of Turbine Stator and Rotor Cascades

1995 ◽  
Vol 117 (4) ◽  
pp. 553-561 ◽  
Author(s):  
A. Yamamoto ◽  
R. Murao ◽  
Y. Suzuki ◽  
Y. Aoi
Keyword(s):  
Suction Side ◽  
Secondary Flows ◽  
Relative Location ◽  
Flow Measurements ◽  
Tip Leakage ◽  
Turbine Stator ◽  
Wake Interaction ◽  
In Series ◽  
Cascade Interaction ◽  
Made In

Detailed flow measurements were made to study cascade interaction of turbine stator and rotor, using two linear cascades installed in series. The upstream cascade was moved to several places in the cascade pitchwise direction in order to change the relative location between the two cascades, and measurements were made in the downstream cascade. The result shows that the net total pressure loss generated in the downstream cascade becomes maximum when wakes of the upstream cascade pass the suction side of the downstream cascade passage, while the tip leakage loss generated in the downstream cascade does not change with the relative location of the cascades. The upstream cascade wakes interact with the secondary flows and most strongly with the endwall flow in the downstream cascade passage, making the loss distributions in the cascades fairly unsteady.

Pressure Gradient and Leading Edge Effects on the Corner Boundary Layer

1979 ◽  
Vol 30 (3) ◽  
pp. 471-484 ◽  
Author(s):  
M. Zamir ◽  
A.D. Young
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flow Direction ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Flat Plates ◽  
Low Reynolds Numbers ◽  
Small Incidence ◽  
Made In

SummaryResults are presented of velocity and pressure measurements made in the initially laminar boundary layer in a streamwise corner formed by two flat plates at 90° to each other set at various incidences. The leading edges of the plates were sharp in contrast to earlier tests with an aerofoil type leading edge. It was found impossible to obtain a steady enough flow for useful measurements to be made at zero incidence and pressure gradient, a small incidence associated with a favourable pressure gradient was necessary. This is believed to be because of the development of separation bubbles at the sharp leading edge at very small incidences due to small variations of flow direction to be expected in a wind tunnel. The profiled nose used in earlier tests afforded flow conditions much closer to the ideal theoretical model involving zero pressure gradient, but it is argued that any nose however shaped may introduce disturbances in the form of characteristic secondary flows that may well determine the downstream response of the boundary layer. In any case the corner flow is highly unstable at all but very low Reynolds numbers, and in the absence of a region of favourable pressure gradient a Reynolds number in terms of distance downstream of the leading edge greater than about 105is unlikely to be attained in practice with the flow remaining smooth and laminar.

Measurements on turbulent vortices in a cylinder wake

1966 ◽  
Vol 294 (1438) ◽  
pp. 319-342 ◽  
Keyword(s):  
Inner Core ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Core Region ◽  
Circular Cylinders ◽  
Cylinder Wake ◽  
Hot Wire ◽  
Mean Flow ◽  
Flow Measurements ◽  
Made In

The wakes of circular cylinders were explored by means of hot wire anemometers in the range of Reynolds numbers based on diameter of from 10 3 to 4 x 10 4 . The vortex strength was determined and its variation with distance downstream and with Reynolds number was investigated. The vortex strengths agree with those obtained by application of Roshko’s (1954) method to our mean flow measurements. The vortex velocity distribution assumed was that of Hoffman & Joubert (1963) which was found to agree with our measurements when slight adjustments were made in the inner core region. Vortex paths, the formation region and three dimensional effects are also discussed.

A Quasi Unsteady Study on Wake Interaction of Turbine Stator and Rotor Cascades

1994 ◽  
Author(s):  
Atsumasa Yamamoto ◽  
Rin-ichi Murao ◽  
Yuji Suzuki ◽  
Yoshihiro Aoi
Keyword(s):  
Suction Side ◽  
Secondary Flows ◽  
Relative Location ◽  
Flow Measurements ◽  
Tip Leakage ◽  
Turbine Stator ◽  
Wake Interaction ◽  
In Series ◽  
Cascade Interaction ◽  
Made In

Detailed flow measurements were made to study cascade interaction of turbine stator and rotor, by using two linear cascades installed in series. The upstream cascade was traversed at several times in the cascade pitchwise direction in order to change the relative location between the two cascades, and measurements were made in the downstream cascade. The result shows that the net total pressure loss generated in the downstream cascade becomes maximum when wakes of the upstream cascade pass the suction side of the downstream cascade passage, while the tip leakage loss generated in the downstream cascade does not change with the relative location th cascades. The upstreaof born cascade wakes interact with the secondary flows, and most strongly with the endwall flow in the downstream cascade passage, making the loss distributions in both cascades fairly unsteady.

Comparative Arterial Antithrombotic Activity of Clopidogrel and Acetyl Salicylic Acid in the Pig

1992 ◽  
Vol 68 (05) ◽  
pp. 500-505 ◽  
Author(s):  
Ch M Samama ◽  
Ph Bonnin ◽  
M Bonneau ◽  
G Pignaud ◽  
E Mazoyer ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Femoral Artery ◽  
Bleeding Time ◽  
Ex Vivo ◽  
Flow Reduction ◽  
Cyclic Flow ◽  
Left Femoral Artery ◽  
Before And After ◽  
The Right ◽  
Induced Aggregation

SummaryWe investigated the comparative antithrombotic properties of clopidogrel, an analogue of ticlopidine, and aspirin, using the Folts' model on femoral arteries in 22 pigs. On each animal, clopidogrel or aspirin were used to treat the thrombotic process on the left femoral artery and to prevent this process on the right femoral artery. Sequentially: an injury and stenosis were carried out on the left femoral artery; the thrombotic process was monitored with a Doppler during a 30-min observation period for cyclic flow reductions or permanent cessation of flow; after the first cyclic flow reduction occurred, clopidogrel (5 mg kg-1) or aspirin (2.5, 5, 100 mg kg-1) were injected intravenously; if cyclic flow reductions were abolished, epinephrine (0.4 µg kg-1 min-1) was injected to try to restore cyclic flow reductions and/or permanent cessation of flow; then injury and stenosis were applied on the right femoral artery. Before and after injection of clopidogrel or aspirin, ear immersion bleeding times and ex-vivo platelet aggregation were performed. Clopidogrel (n = 7) abolished cyclic flow reductions in all animals and epinephrine did not restore any cyclic flow reduction. On the right femoral artery, cyclic flow reductions were efficiently prevented, even for two injuries. Basal bleeding time (5 min 28) was lengthened (>15 min, 30 min after clopidogrel and remained prolonged even after 24 h). ADP-induced platelet aggregation was inhibited (more than 78%). Comparatively, aspirin had a moderate and no dose-dependent effect. Aspirin 2.5 mg kg-1 (n = 6) abolished cyclic flow reductions in 2 animals, CFR reoccurred spontaneously in one animal and epinephrine restored it in a second animal. Aspirin 5 mg kg-1 (n = 6) abolished cyclic flow reductions in only 3 animals and epinephrine always restored it. Aspirin 100 mg kg-1 (n = 3) was unable to abolish cyclic flow reductions. On the right femoral artery, aspirin did not significantly prevent cyclic flow reductions which occurred in all animals after one (n = 14) or two injuries (n = 1), except for one animal. Basal bleeding time was lengthened but it shortened rapidly, reaching its basal value after 24 h. ADP-induced aggregation was not significantly inhibited, whereas arachidonic acid induced aggregation was always inhibited. Clopidogrel appears as a more potent antithrombotic drug than aspirin in this model, in treating and preventing spontaneous or epinephrine-induced cyclic flow reductions and lengthening bleeding time.

scholarly journals Focusing of Particles in a Microchannel with Laser Engraved Groove Arrays

Biosensors ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 263
Author(s):  
Tianlong Zhang ◽  
Yigang Shen ◽  
Ryota Kiya ◽  
Dian Anggraini ◽  
Tao Tang ◽  
...  
Keyword(s):  
Open Space ◽  
Lateral Displacement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Particle Sedimentation ◽  
Nanoparticle Separation ◽  
Wide Range ◽  
Fs Laser ◽  
Channel Bottom ◽  
Myoblast Cells

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

scholarly journals On the Scope of Lagrangian Vortex Methods for Two-Dimensional Flow Simulations and the POD Technique Application for Data Storing and Analyzing

Entropy ◽  
2021 ◽  
Vol 23 (1) ◽  
pp. 118
Author(s):  
Kseniia Kuzmina ◽  
Ilia Marchevsky ◽  
Irina Soldatova ◽  
Yulia Izmailova
Keyword(s):  
Flow Simulation ◽  
Internal Flow ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Vortex Methods ◽  
Flow Simulations ◽  
Additional Information ◽  
Two Dimensional Flow ◽  
Different Shapes ◽  
Problem Formulations

The possibilities of applying the pure Lagrangian vortex methods of computational fluid dynamics to viscous incompressible flow simulations are considered in relation to various problem formulations. The modification of vortex methods—the Viscous Vortex Domain method—is used which is implemented in the VM2D code developed by the authors. Problems of flow simulation around airfoils with different shapes at various Reynolds numbers are considered: the Blasius problem, the flow around circular cylinders at different Reynolds numbers, the flow around a wing airfoil at the Reynolds numbers 104 and 105, the flow around two closely spaced circular cylinders and the flow around rectangular airfoils with a different chord to the thickness ratio. In addition, the problem of the internal flow modeling in the channel with a backward-facing step is considered. To store the results of the calculations, the POD technique is used, which, in addition, allows one to investigate the structure of the flow and obtain some additional information about the properties of flow regimes.

scholarly journals Steady flow separation patterns in a 45 degree junction

2000 ◽  
Vol 411 ◽  
pp. 1-38 ◽  
Author(s):  
C. ROSS ETHIER ◽  
SUJATA PRAKASH ◽  
DAVID A. STEINMAN ◽  
RICHARD L. LEASK ◽  
GREGORY G. COUCH ◽  
...  
Keyword(s):  
Flow Separation ◽  
Stokes Equations ◽  
Bypass Graft ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Measured Velocity ◽  
Curved Tube

Numerical and experimental techniques were used to study the physics of flow separation for steady internal flow in a 45° junction geometry, such as that observed between two pipes or between the downstream end of a bypass graft and an artery. The three-dimensional Navier–Stokes equations were solved using a validated finite element code, and complementary experiments were performed using the photochromic dye tracer technique. Inlet Reynolds numbers in the range 250 to 1650 were considered. An adaptive mesh refinement approach was adopted to ensure grid-independent solutions. Good agreement was observed between the numerical results and the experimentally measured velocity fields; however, the wall shear stress agreement was less satisfactory. Just distal to the ‘toe’ of the junction, axial flow separation was observed for all Reynolds numbers greater than 250. Further downstream (approximately 1.3 diameters from the toe), the axial flow again separated for Re [ges ] 450. The location and structure of axial flow separation in this geometry is controlled by secondary flows, which at sufficiently high Re create free stagnation points on the model symmetry plane. In fact, separation in this flow is best explained by a secondary flow boundary layer collision model, analogous to that proposed for flow in the entry region of a curved tube. Novel features of this flow include axial flow separation at modest Re (as compared to flow in a curved tube, where separation occurs only at much higher Re), and the existence and interaction of two distinct three-dimensional separation zones.

Self-sealing, Large Bore Arterial Punctures: A Counterintuitive New Phenomenon

2002 ◽  
Vol 124 (4) ◽  
pp. 342-346
Author(s):  
Blayne A. Roeder ◽  
Charles F. Babbs ◽  
William E. Schoenlein ◽  
Klod Kokini ◽  
Farshid Sadeghi
Keyword(s):  
Cardiac Catheterization ◽  
Femoral Artery ◽  
Standard Technique ◽  
Needle Insertion ◽  
Catheter Removal ◽  
Intraluminal Pressure ◽  
Modified Technique ◽  
Modeling Studies ◽  
Made In ◽  
Flap Valve

The human femoral artery can bleed dangerously following the removal of a catheter during cardiac catheterization. In this study, a modified technique of needle insertion, simply inserting the needle bevel-down instead of the standard bevel-up approach, was tested as a means to reduce bleeding after catheter removal. Large bore needle punctures were made in surgically exposed arteries of anesthetized pigs using either a standard technique (45 degree approach, bevel up) or a modified technique (25 degree approach, bevel down). For half the punctures, topical phenylephrine solution (1 mg/ml) was applied to the adventitia of the artery to cause constriction. Median bleeding rates were reduced from 81 to less than 1 ml/min/100 mmHg intraluminal pressure by the modified technique with application of phenylephrine. In most cases zero bleeding, that is self-sealing, of the arteries occurred. It is postulated that a flap-valve of tissue created by the modified technique produced this self-sealing behavior. Sophisticated modeling studies are needed to fully understand this new phenomenon.

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