Vortex Generation in Pulsatile Flow Through Arterial Bifurcation Models Including the Human Carotid Artery

1988 ◽  
Vol 110 (3) ◽  
pp. 166-171 ◽  
Author(s):  
Takayoshi Fukushima ◽  
Tatsuji Homma ◽  
Kiyohito Harakawa ◽  
Noriyuki Sakata ◽  
Takehiko Azuma
Keyword(s):  
Steady Flow ◽  
Pulsatile Flow ◽  
Separation Bubble ◽  
Vortex Formation ◽  
Flow Distribution ◽  
Horseshoe Vortex ◽  
Helical Flow ◽  
Elastic Tube ◽  
Recirculating Flow ◽  
Flow Through

Visualization experiments were performed to elucidate the complicated flow pattern in pulsatile flow through arterial bifurcations. Human common carotid arteries, which were made transparent, and glass-models simulating Y- and T-shaped bifurcations were used. Pulsatile flow with wave forms similar to those of arterial flow was generated with a piston pump, elastic tube, airchamber, and valves controlling the outflow resistance. Helically recirculating flow with a pattern similar to that of the horseshoe vortex produced around wall-based protuberances in circular tubes was observed in pulsatile flow through all the bifurcations used in the present study. This flow type, which we shall refer to as the horseshoe vortex, has also been demonstrated to occur at the human common carotid bifurcation in steady flow with Reynolds numbers above 100. Time-varying flows also produced the horseshoe vortex mostly during the decelerating phase. Fluid particles of dye solution approaching the bifurcation apex diverged, divided into two directions perpendicularly, and then showed helical motion representing the horseshoe vortex formation. While this helical flow was produced, the stagnation points appeared on the wall upstream of the apex. Their position was dependent upon the flow distribution ratio between the branches in the individual arteries. The region affected by the horseshoe vortex was smaller during pulsatile flow than during steady flow. Lowering the Reynolds number together with the Womersley number weakened the intensity of helical flow. A separation bubble, resulting from the divergence or wall roughness, was observed at the outer or inner wall of the branch vessels and made the flow more complicated.

CFD Analysis Comparing Steady Flow and Pulsatile Flow Through the Aorta and its Main Branches

2016 ◽  
Author(s):  
John D. Martin
Keyword(s):  
Blood Flow ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Close Association ◽  
Beating Heart ◽  
Pressure Data ◽  
Heart Model ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Very High

A computational fluid dynamics (CFD) study has been done comparing pulsatile and non-pulsatile blood flow through the aortic arch and its main branches. The pulsatile flow was to mimic the blood flow due to a beating heart and the non-pulsatile or steady flow was to mimic cardiopulmonary bypass (CPB). The purpose of the study was too narrow in on possible reasons CPB may contribute to the development of atherosclerosis. The main focus of the study was to look at the wall shear stress (WSS) values due to their close association with the development of atherosclerosis. In addition velocity and pressure data were also analyzed. The results of this study showed a stark contrast between the WSS values between the CPB model and the beating heart model. The CPB model did not have any points of oscillating WSS combined with the fact that there were regions of very high and very low constant WSS values in comparison with the beating heart analysis suggests that there may be potential for atherosclerotic development or plaque buildup within the artery. The beating heart model showed a range of WSS values within the aorta that were much lower overall compared with the CPB model.

Analysis of Fully Developed Unsteady Viscous Flow in a Curved Elastic Tube Model to Provide Fluid Mechanical Data for Some Circulatory Path-Physiological Situations and Assist Devices

1979 ◽  
Vol 101 (2) ◽  
pp. 114-123 ◽  
Author(s):  
K. B. Chandran ◽  
R. R. Hosey ◽  
D. N. Ghista ◽  
V. W. Vayo
Keyword(s):  
Shear Stress ◽  
Unsteady Flow ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Patterns ◽  
Elastic Tube ◽  
Flow Component ◽  
Flow Response ◽  
Elastic Tubes ◽  
Flow Components

The unsteady and steady flow components of pulsatile flow response, to an experimentally monitored representative pressure pulse, are computed to provide fluid mechanical data for the etiology of arteriosclerosis at arterial curvature sites and for the design analysis of some extracorporeal dialysis and oxygenatory systems. The unsteady flow component of pulsatile flow in curved elastic tubes is simulated by the superposition of the first six Fourier components of a derived oscillatory flow solution of a viscous, incompressible fluid through an elastic tube of small curvature. The computer flow patterns, wall shear stress and hoop and axial stresses in the wall, due to unsteady and steady flow components of pulsatile flow response, are compared and their implications are discussed. The results show that the unsteady component yields shear stress of an order of magnitude greater than the steady flow, but the steady flow component has a greater variation in the shear stress distribution over a cross section. The steady and unsteady flow patterns are presented for several values of the tube diameters and curvature parameters typical of major arteries in the human circulatory system. The flow pattern and the stress variations could also prove useful in the design of extracorporeal systems such as dialysis machines and oxygenators.

Experimental Investigation of Pulsatile Flow Through Prosthetic Heart Valves

2013 ◽  
Author(s):  
Oleksandr Barannyk ◽  
Satya Karri ◽  
Peter Oshkai
Keyword(s):  
Flow Visualization ◽  
Pulsatile Flow ◽  
Flow Instability ◽  
Artificial Heart Valve ◽  
Prosthetic Heart Valves ◽  
Aortic Sinus ◽  
Vortical Structures ◽  
Recirculating Flow ◽  
Viscous Shear ◽  
Flow Through

Qualitative and quantitative flow visualization study was conducted for the case of a biomimetic pulsatile flow through an artificial heart valve placed into an asymmetric model of an aortic root with sinuses of Valsalva. A prototype trileaflet valve was tested alongside with a tilted disk valve and a bileaflet valve. The study was conducted in test conditions corresponding to 70 beats/min, 5.5 l/min target cardiac output and a mean aortic pressure of 100 mmHg. Flow visualization data obtained using digital particle image velocimetry (PIV) was phase-averaged in order to provide accurate, time-resolved patterns of flow velocity and viscous shear stress values. In the case of the tri-leaflet valve, during systole, a stable jet emanates from the valve, with vortical structures forming on the sides of the jet. These vortical structures entrain the surrounding fluid into the jet, which leads to development of a shear flow instability downstream of the valve. For all considered valve types, a recirculating flow was observed in the sinus area during both the systole and the diastole. No indication of a stagnating flow region was observed, as the fluid was completely washed out from the aortic sinus within each cardiac cycle.

Pulsatile Flow and Mass Transport Over an Array of Cylinders: Gas Transfer in a Cardiac-Driven Artificial Lung

2005 ◽  
Vol 128 (1) ◽  
pp. 85-96 ◽  
Author(s):  
Kit Yan Chan ◽  
Hideki Fujioka ◽  
Robert H. Bartlett ◽  
Ronald B. Hirschl ◽  
James B. Grotberg
Keyword(s):  
Pressure Drop ◽  
Steady Flow ◽  
Void Fraction ◽  
Pulsatile Flow ◽  
Fiber Bundle ◽  
Gas Transfer ◽  
Right Heart ◽  
Flow Through ◽  
The Right ◽  
Array Geometry

The pulsatile flow and gas transport of a Newtonian passive fluid across an array of cylindrical microfibers are numerically investigated. It is related to an implantable, artificial lung where the blood flow is driven by the right heart. The fibers are modeled as either squared or staggered arrays. The pulsatile flow inputs considered in this study are a steady flow with a sinusoidal perturbation and a cardiac flow. The aims of this study are twofold: identifying favorable array geometry/spacing and system conditions that enhance gas transport; and providing pressure drop data that indicate the degree of flow resistance or the demand on the right heart in driving the flow through the fiber bundle. The results show that pulsatile flow improves the gas transfer to the fluid compared to steady flow. The degree of enhancement is found to be significant when the oscillation frequency is large, when the void fraction of the fiber bundle is decreased, and when the Reynolds number is increased; the use of a cardiac flow input can also improve gas transfer. In terms of array geometry, the staggered array gives both a better gas transfer per fiber (for relatively large void fraction) and a smaller pressure drop (for all cases). For most cases shown, an increase in gas transfer is accompanied by a higher pressure drop required to power the flow through the device.

Steady flow through porous media

AIChE Journal ◽  
1981 ◽  
Vol 27 (4) ◽  
pp. 529-545 ◽  
Author(s):  
R. A. Greenkorn
Keyword(s):  
Porous Media ◽  
Steady Flow ◽  
Flow Through Porous Media ◽  
Flow Through

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

A Topological Study of the Genesis of a Horseshoe Vortex in the Symmetry Plane Due to an Adverse Pressure Gradient

2001 ◽  
Author(s):  
Martijn A. van den Berg ◽  
Michael M. J. Proot ◽  
Peter G. Bakker
Keyword(s):  
Pressure Gradient ◽  
Bifurcation Theory ◽  
Nonlinear Differential Equations ◽  
Nonlinear Dynamical System ◽  
Symmetry Plane ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Nonlinear Dynamical ◽  
Separating Flow ◽  
Flow Through

Abstract The present paper describes the genesis of a horseshoe vortex in the symmetry plane in front of a juncture. In contrast to a previous topological investigation, the presence of the obstacle is no longer physically modelled. Instead, the pressure gradient, induced by the obstacle, has been used to represent its influence. Consequently, the results of this investigation can be applied to any symmetrical flow above a flat plate. The genesis of the vortical structure is analysed by using the theory of nonlinear differential equations and the bifurcation theory. In particular, the genesis of a horseshoe vortex can be described by the unfolding of the degenerate singularity resulting from a Jordan Normal Form with three vanishing eigenvalues and one linear term which is related to the adverse pressure gradient. The examination of this nonlinear dynamical system reveals that a horseshoe vortex emanates from a non-separating flow through two subsequent saddle-node bifurcations in different directions and the transition of a node into a focus located in the flow field.

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