Flow patterns of the fully developed pulsatile flow in a curved pipe.

Abstract Vascular stents are being used in increasing numbers to correct arterial flow limiting disorders. Although data exist on the in vivo performance of these devices, comparatively little is known about how these devices affect the arterial mechanical environment. The long-term success of stenting is very likely affected by the blood flow patterns and artery wall stresses that follow stent placement. This study was undertaken to identify the mechanical environment in stented arteries and to propose a stent design that minimizes the “mechanical trauma” of stent implantation. A series of pulsatile flow visualization experiments were performed with a Johnson & Johnson Palmaz/Schatz stent inserted in a straight compliant tube. A flow loop was constructed that was capable of applying a physiologic pulsatile flow indicative of conditions in the femoral or coronary arteries. The results showed that this stent design creates complex flow patterns including large-scale vortices, and that these patterns are caused by the compliance mismatch between the stented vessel and adjacent unstented vessel. The compliance mismatch also would be expected to create abnormal stress concentrations in the artery wall near the ends of the stent. A simplified model of an artery was constructed to estimate the stress in the artery wall. The stent/artery structure was assumed to be an axisymmetric thin shell made of a linear elastic, orthotropic material that undergoes small deformations. The stent diameter was assumed to be equal to the artery systolic diameter. The stresses were estimated under diastolic pressure, when the deflection of the artery due to the presence of the stent is greatest. It was found that the circumferential and axial stresses at the ends of the stent were 2 to 3 times higher than the stress far from the stent. Based on these mechanical studies, a new stent design was proposed that provides a smooth transition in compliance at the proximal and distal ends of the tube. Flow visualization studies with this new stent indicate that the flow disturbances are greatly reduced with this new design. The transition zone was incorporated into the shell model to estimate the artery wall stresses induced by this new model. It was found that the stress concentration was reduced by as much as 36% from the rigid stent value. These studies demonstrate the potential complexity of flow in stented arteries and provide some recommendations for optimizing stent design from a biomechanical point of view. This work was supported in part by a Linkage Grant from NATO.

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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

Journal of Biomechanical Engineering ◽

10.1115/1.3426232 ◽

1979 ◽

Vol 101 (2) ◽

pp. 114-123 ◽

Cited By ~ 10

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.

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VISUALIZATION OF DEVELOPING SECONDARY FLOW PATTERNS IN THE HYDRODYNAMIC ENTRANCE REGION OF A CURVED PIPE

Journal of Flow Visualization and Image Processing ◽

10.1615/jflowvisimageproc.v2.i1.10 ◽

1995 ◽

Vol 2 (1) ◽

pp. 1-13 ◽

Cited By ~ 1

Author(s):

K. C. Cheng ◽

Masao Takuma ◽

Yoshiyuki Kamiya

Keyword(s):

Secondary Flow ◽

Flow Patterns ◽

Entrance Region ◽

Curved Pipe

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Flow Visualization Experiments on Secondary Flow Patterns in an Isothermally Heated Curved Pipe

Journal of Heat Transfer ◽

10.1115/1.3248067 ◽

1987 ◽

Vol 109 (1) ◽

pp. 55-61 ◽

Cited By ~ 13

Author(s):

K. C. Cheng ◽

F. P. Yuen

Keyword(s):

Flow Visualization ◽

Secondary Flow ◽

Theoretical Models ◽

Flow Patterns ◽

Radius Of Curvature ◽

Dean Number ◽

Number Range ◽

Curved Pipe ◽

Curved Pipes ◽

Numerical Predictions

Secondary flow patterns at the exit of a 180 deg bend (tube inside diameter d = 1.99 cm, radius of curvature Rc = 10.85 cm) are presented to illustrate the combined effects of centrifugal and buoyancy forces in hydrodynamically and thermally developing entrance region of an isothermally heated curved pipe with both parabolic and turbulent entrance velocity profiles. Three cases of upward, horizontal, and downward-curved pipe flows are studied for constant wall temperatures Tw=55–91°C, Dean number range K=22–1209 and ReRa=1.00×106–8.86×107. The flow visualization was realized by the smoke injection method. The secondary flow patterns shown are useful for future comparison with numerical predictions and confirming theoretical models. The results can be used to assess qualitatively the limit of the applicability of the existing correlation equations for laminar forced convection in isothermally heated curved pipes without buoyancy effects.

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Transport Phenomena of Pulsatile Flow in a Curved Pipe.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.58.2074 ◽

1992 ◽

Vol 58 (551) ◽

pp. 2074-2079

Author(s):

Shigeru TADA ◽

Shuzo OSHIMA ◽

Ryuichiro YAMANE

Keyword(s):

Pulsatile Flow ◽

Transport Phenomena ◽

Curved Pipe

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Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

Journal of Biomechanical Engineering ◽

10.1115/1.4006984 ◽

2012 ◽

Vol 134 (7) ◽

Cited By ~ 3

Author(s):

N. K. C. Selvarasu ◽

Danesh K. Tafti

Keyword(s):

Shear Stress ◽

Coronary Artery ◽

Wall Shear Stress ◽

Secondary Flow ◽

Pulsatile Flow ◽

Flow Patterns ◽

Shear Stresses ◽

Wall Shear ◽

Vorticity Flux ◽

Curvature And Torsion

Cardiovascular diseases are the number one cause of death in the world, making the understanding of hemodynamics and the development of treatment options imperative. The effect of motion of the coronary artery due to the motion of the myocardium is not extensively studied. In this work, we focus our investigation on the localized hemodynamic effects of dynamic changes in curvature and torsion. It is our objective to understand and reveal the mechanism by which changes in curvature and torsion contribute towards the observed wall shear stress distribution. Such adverse hemodynamic conditions could have an effect on circumferential intimal thickening. Three-dimensional spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries were carried out for a simplified coronary artery with physiologically relevant flow parameters. A model with stationary walls is used as the baseline control case. In order to study the effect of curvature and torsion variation on local hemodynamics, this baseline model is compared to models where the curvature, torsion, and both curvature and torsion change. The simulations provided detailed information regarding the secondary flow dynamics. The results suggest that changes in curvature and torsion cause critical changes in local hemodynamics, namely, altering the local pressure and velocity gradients and secondary flow patterns. The wall shear stress (WSS) varies by a maximum of 22% when the curvature changes, by 3% when the torsion changes, and by 26% when both the curvature and torsion change. The oscillatory shear stress (OSI) varies by a maximum of 24% when the curvature changes, by 4% when the torsion changes, and by 28% when both the curvature and torsion change. We demonstrate that these changes are attributed to the physical mechanism associating the secondary flow patterns to the production of vorticity (vorticity flux) due to the wall movement. The secondary flow patterns and augmented vorticity flux affect the wall shear stresses. As a result, this work reveals how changes in curvature and torsion act to modify the near wall hemodynamics of arteries.

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