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The steady flow in an anatomically realistic human carotid bifurcation was simulated numerically. Main parameters such as wall shear stress (WSS), velocity profiles and pressure distributions are investigated in the carotid artery, namely in bifurcation and sinusoidal enlargement regions. Flow in the carotid sinus is dominated by a single secondary vortex motion accompanied by a strong helical flow. This type of flow is induced primarily by the curvature and asymmetry of the in vivo geometry. Low wall shear stress concentration occurs at both the anterior and posterior aspects of the proximal internal bulb. [ABSTRACT FROM AUTHOR]

Tortuous saphenous vein graft (SVG) hemodynamics was investigated using computational fluid dynamics (CFD) techniques. Computed tomography (CT) technology is used for non-invasive bypass graft assessment 7 days after surgery. CT investigation shown two regions with severe shape remodelling first is an elbow type contortion and second is a severe curvature with tortuous area reduction. In conclusion, the helical flow induced by vessel torsion may stabilize the blood flow in the distal part of the SVG, reducing the flow disturbance and suppressing the flow separation, but in the distal end of the graft, promote the inflammatory processes in the vessels. [ABSTRACT FROM AUTHOR]

Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. The impact of flow alterations around struts vary as the strut geometrical parameters change. Our results provide data regarding the hemodynamic parameters for the blood flow in both stenosed and stented coronary artery under physiological conditions, namely wall shear stress and pressure drop. [ABSTRACT FROM AUTHOR]

Optimal graft design has been an objective of many researchers in order to find correlations between hemodynamics and graft failure. The character of complex vortex structures created in the area between the heel and occluded section depends on the flow parameters (for the case of straight graft). We can identify two vortices in the symmetry plane (proximal and distal to the anastomosis). [ABSTRACT FROM AUTHOR]

Luminally protruding struts alter blood flow, creating areas of recirculation, separation, and stagnation. The impact of flow alterations around struts vary as the strut geometrical parameters change. We quantified the influence of the luminal flow alterations due to the presence of the stent struts by performing two-dimensional numerical simulation. Idealized computer models can facilitate understanding of the in-stent restenosis that is impossible to achieve in vivo. [ABSTRACT FROM AUTHOR]

Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. Strut shape, strut thickness and the distance between consecutive struts have been associated clinically with the with post-intervention clinical outcomes. Hemodynamically favorable designs according to computational modeling can reduced in-stent restenosis after coronary stenting intervention. [ABSTRACT FROM AUTHOR]

Luminally protruding struts alter blood flow, creating areas of recirculation, separation, and stagnation. The impact of flow alterations around struts vary as the strut geometrical parameters change. We quantified the influence of the luminal flow alterations due to the presence of the stent struts by performing two-dimensional numerical simulation. Idealized computer models can facilitate understanding of the in-stent restenosis that is impossible to achieve in vivo. [ABSTRACT FROM AUTHOR]

Optimal graft design has been an objective of many researchers in order to find correlations between hemodynamics and graft failure. The character of complex vortex structures created in the area between the heel and occluded section depends on the flow parameters (for the case of straight graft). We can identify two vortices in the symmetry plane (proximal and distal to the anastomosis). [ABSTRACT FROM AUTHOR]

Local hemodynamic factors are known affect the natural history of the restenosis critically after coronary stenting of atherosclerosis. Stent-induced flows disturbance magnitude dependent directly on the strut design. Strut shape, strut thickness and the distance between consecutive struts have been associated clinically with the with post-intervention clinical outcomes. Hemodynamically favorable designs according to computational modeling can reduced in-stent restenosis after coronary stenting intervention. [ABSTRACT FROM AUTHOR]

In the present work, numerical analysis is performed in a helically sinuous tube with circular cross-section and a finite pitch under laminar flow conditions. The evolution of flows in three helically sinuous tubes at Re = 500 was studied taking into account the effects of torsion and curvature. Results show that in terms of axial velocity, the curvature and the torsion of the helical geometry affect the flow fields. In geometry model no 1 with small curvature and small torsion, symmetric vortex pattern is observed. Increasing the curvature and the torsion an asymmetric vortex model for a predominantly single vortex result. [ABSTRACT FROM AUTHOR]

Secondary flows in curved rectangular ducts with diminishing cross sections are numerically studied. Development of secondary flow in curved rectangular regular cross-sectional area duct is studied using an improved finite difference scheme for solving parabolized Navier-Stokes equations is presented. This scheme has its origin in the work of Briley, which is based on classical ADI method to march the solution in the streamwise direction. With some modifications, it is shown in the present work that the stability of this scheme is greatly enhanced. Its applicability is considerably increased. Results with various sb. and sa for two different aspect ratio are given. Note the parameters asa and bsb, where sa is scaling factor for the width of the duct sb is scaling factor for the height of the duct, respectively. Dean number of 54 is used for the comparisons. [ABSTRACT FROM AUTHOR]

Confluence zones in rivers are common occurrence in natural rivers, and its flow structure, especially secondary flow, has much impact on sediment transport and pollutant dispersion in confluence region. Flume experiment studies have proved the variation of separation zone from the water surface to the bottom, but there are little numerical simulation studies on the scale of separation zone. As the developing of computational fluid dynamics, there are several models to simulate the turbulence properties in the river. This paper uses the standard k-e, RNG k-e and RSM turbulence model to simulate the secondary flow and separation zone in the confluence river, and compared the results with the experiment data quantification ally. [ABSTRACT FROM AUTHOR]

Unsteady wake represents blade pneumatic load and affects turbine characteristic greatly, while secondary flow loss is the main part of turbine endwall loss. The appearance, attenuation of unsteady wake and their interaction with downstream secondary flow have significant effect on turbine design and characteristic. Experiment measurement and numerical simulation are adopted to study secondary flow and wake. Upstream rotating blade can be replaced by cylinder with the same wake velocity and stagnant pressure loss. In experiment, two inlet velocities are taken to study the effect of inlet flux on blade characteristic. At the same time, upstream cylinders move quarter of circumferential pitch discretely and the influence of upstream cylinder wake to downstream blade is researched. Afterwards, two hollow boards are used to cover part of blade height to show tip and bottom secondary vortexes alternation under different relative blade height. First, the system integrating method of hotwire measurement is developed with a rotating slanted hotwire in order to measure three-dimensions flow field at blade outlet. The procedure for solving the mean velocity vector involving the least-squares technique can be accomplished via the LSQNONLIN optimization function of Matlab. Then the whole velocity field of horizontal-flow and perpendicular plane has been measured with a Particle Image Velocimetry (PIV). Finally, numerical calculation is carried out. The result shows coincidence between experiment and calculation. It is found that outlet secondary flow is obvious and severe at higher inlet velocity and smallest relative blade height. When the upstream rotor wake impinges upon the leading edge of the down stream stator, the corresponding stage efficiency will be higher, when the upstream wake is transferred into the mid passage of the downstream stator, the corresponding stage efficiency will be lower. As a result, the optimal blade circumferential layout is an effective way to increase turbine pneumatic efficiency. The numerical calculation shows that pressure pulse intensity on pressure side weakens rapidly along blade profile, while pressure pulse intensity on suction side weakens along profile first and then strengthen due to unsteady separation on trail edge. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]