Large Curvature Effect on Pulsatile Entrance Flow in a Curved Tube: Model Experiment Simulating Blood Flow in an Aortic Arch

1996 ◽  
Vol 118 (2) ◽  
pp. 180-186 ◽  
Author(s):  
T. Naruse ◽  
K. Tanishita
Keyword(s):  
Blood Flow ◽  
Aortic Arch ◽  
Maximum Velocity ◽  
Curvature Radius ◽  
Wall Region ◽  
Dean Number ◽  
Large Curvature ◽  
Curved Tube ◽  
Wall Shear ◽  
Entrance Flow

We measured the velocity profiles of pulsatile entrance flow in a strongly curved tube using a laser-Doppler anemometer in order to simulate blood flow in the aortic arch under various conditions, i.e., a ratio of tube to curvature radius of 1/3, Womersley parameters of 12 and 18, and peak Dean number up to 1200. Axial isovelocity contours of the cross-section showed the potential vortex to be near the entrance, and with the maximum velocity there being skewed towards the inner wall; thereafter shifting towards the outer wall. During the deceleration phase, reverse axial flow occurred near the inner wall, and a region of this flow extended downstream. The large curvature contributes to the enhancement of the secondary flow and flow reversal, which elevates the wall-shear stress oscillations. The location of elevated wall-shear oscillations corresponds to the vessel wall region where atherosclerotic formation frequently occurs; thereby indicating that both the large curvature and pulsatility play key roles in formation of localized atherosclerotic lesions.

Blood Flow Manipulation in the Aorta With Coarctation and Arch Narrowing for Pediatric Subjects

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Yuxi Jia ◽  
Kumaradevan Punithakumar ◽  
Michelle Noga ◽  
Arman Hemmati
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Arch ◽  
Flow Direction ◽  
Upper Body ◽  
Patient Specific ◽  
Shear Stresses ◽  
Wall Shear

Abstract The characteristics of blood flow in an abnormal pediatric aorta with an aortic coarctation and aortic arch narrowing are examined using direct numerical simulations and patient-specific boundary conditions. The blood flow simulations of a normal pediatric aorta are used for comparison to identify unique flow features resulting from the aorta geometrical anomalies. Despite flow similarities compared to the flow in normal aortic arch, the flow velocity decreases with an increase in pressure, wall shear stress, and vorticity around both anomalies. The presence of wall shear stresses in the trailing indentation region and aorta coarctation opposing the primary flow direction suggests that there exist recirculation zones in the aorta. The discrepancy in relative flowrates through the top and bottom of the aorta outlets, and the pressure drop across the coarctation, implies a high blood pressure in the upper body and a low blood pressure in the lower body. We propose using flow manipulators prior to the aortic arch and coarctation to lower the wall shear stress, while making the recirculation regions both smaller and weaker. The flow manipulators form a guide to divert and correct blood flow in critical regions of the aorta with anomalies.

Experimental study of wall shear rates in the entry region of a curved tube

1979 ◽  
Vol 93 (3) ◽  
pp. 465-489 ◽  
Author(s):  
U. S. Choi ◽  
L. Talbot ◽  
I. Cornet
Keyword(s):  
Experimental Study ◽  
Cross Section ◽  
Circular Cross Section ◽  
Current Method ◽  
Limiting Current ◽  
Dean Number ◽  
Shear Rates ◽  
Rigid Tube ◽  
Curved Tube ◽  
Wall Shear

Local wall shear rates in steady flow in the entry region of a curved tube have been measured by the electrochemical limiting current method. A semi-circular rigid tube of circular cross-section with radius ratio 1/7 has been employed for a range of Dean number between 139 and 2868. The circumferential and axial distributions of the wall shear rates have been measured at 20° circumferential increments at five different sections of the entry region.

A Numerical Investigation on Pulsatile Blood Flow Through Consecutive Axi-Symmetric Stenosis in Coronary Artery

2010 ◽  
Author(s):  
Seyed Mohammad Javid Mahmoudzadeh Akherat ◽  
Morteza Kimiaghalam
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Velocity Distribution ◽  
Stress Gradient ◽  
Maximum Velocity ◽  
Distribution Patterns ◽  
Velocity Waveform ◽  
Area Reduction ◽  
Wall Shear

The objective of this research is the determination of the wall shear stress (WSS) and velocity distribution patterns in axi-symmetric single or repeated stenoses in coronary arteries. The blood flow is modeled as an incompressible laminar flow with Re = 500 and the analysis is performed for both Newtonian and non-Newtonian blood behaviors. For the single stenosis cases, the area reduction of 25%, 64% and 75% are considered, while for the consecutive stenosis cases two sets of 64%, 25%, and 75%, 64% for the first and second stenosis are examined numerically respectively. Single stenosis cases are also employed for validation purposes, since experimental data are available for them. Present results indicate that regions of high and low shear stress may play an important role in the rupture of atherosclerotic lesions. Both sides of the stenotic area with high WSS and intense WSSG (Wall Shear Stress Gradient) are the most vulnerable sites of plaques. For the cases of consecutive stenoses, results show that displacement of the secondary plauque does not have any effect on the flow pattern. Moreover, the effect of the progression and the area reduction percentage of the consecutive stenoses were studied numerically. It was concluded that the progression of the first and the second stenoses creates high alterations in WSS and velocity distribution and increases the vulnerability of creation of new plaques. Furthermore, the pulsatile property of blood was considered. An accurate velocity waveform was implemented to predict the pulsatile behavior of blood. Results significantly vary from those of the laminar analysis in terms of velocity distribution and the magnitude of the maximum velocity. The flow patterns are studied for several time sections in one period.

Unsteady and Three-Dimensional Simulation of Blood Flow in the Human Aortic Arch

2002 ◽  
Vol 124 (4) ◽  
pp. 378-387 ◽  
Author(s):  
N. Shahcheraghi ◽  
H. A. Dwyer ◽  
A. Y. Cheer ◽  
A. I. Barakat ◽  
T. Rutaganira
Keyword(s):  
Blood Flow ◽  
Aortic Arch ◽  
Thoracic Aorta ◽  
Aortic Wall ◽  
Three Dimensional ◽  
Outer Wall ◽  
Human Aorta ◽  
Shear Stresses ◽  
Descending Thoracic Aorta ◽  
Wall Shear

A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.

scholarly journals Finite Element Modelling of Pulsatile Blood Flow in Idealized Model of Human Aortic Arch: Study of Hypotension and Hypertension

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Paritosh Vasava ◽  
Payman Jalali ◽  
Mahsa Dabagh ◽  
Pertti J. Kolari
Keyword(s):  
Finite Element ◽  
Blood Flow ◽  
Shear Stress ◽  
Aortic Arch ◽  
Human Aorta ◽  
Shear Stresses ◽  
Pulsatile Blood Flow ◽  
Increased Risk ◽  
Pulsatile Pressure ◽  
Wall Shear

A three-dimensional computer model of human aortic arch with three branches is reproduced to study the pulsatile blood flow with Finite Element Method. In specific, the focus is on variation of wall shear stress, which plays an important role in the localization and development of atherosclerotic plaques. Pulsatile pressure pulse is used as boundary condition to avoid flow entry development, and the aorta walls are considered rigid. The aorta model along with boundary conditions is altered to study the effect of hypotension and hypertension. The results illustrated low and fluctuating shear stress at outer and inner wall of aortic arch, proximal wall of branches, and entry region. Despite the simplification of aorta model, rigid walls and other assumptions results displayed that hypertension causes lowered local wall shear stresses. It is the sign of an increased risk of atherosclerosis. The assessment of hemodynamics shows that under the flow regimes of hypotension and hypertension, the risk of atherosclerosis localization in human aorta may increase.

CFD analysis of unsteady and anisotropic turbulent flow in a circular-sectioned 90° bend pipe with and without ribs: A comparative computational study

2021 ◽  
Vol 15 (2) ◽  
pp. 7964-7982
Author(s):  
Rachid Chiremsel ◽  
Ali Fourar ◽  
Fawaz Massouh ◽  
Zakarya Chiremsel
Keyword(s):  
Turbulent Flow ◽  
Axial Velocity ◽  
Computational Study ◽  
Circular Cross Section ◽  
Maximum Velocity ◽  
Curvature Radius ◽  
Reynolds Stresses ◽  
Dean Number ◽  
Number Range ◽  
Bend Pipe

The Reynolds–averaged Navier–Stokes (RANS) equations were solved along with Reynolds stress model (RSM), to study the fully-developed unsteady and anisotropic single-phase turbulent flow in 90° bend pipe with circular cross-section. Two flow configurations are considered the first is without ribs and the second is with ribs attached to solid walls. The number of ribs is 14 ribs regularly placed along the straight pipe. The pitch ratios is 40 and the rib height e (mm) is 10% of the pipe diameter. Both bends have a curvature radius ratio, of 2.0. The solutions of these flows were obtained using the commercial CFD software Fluent at a Dean number range from 5000 to 40000. In order to validate the turbulence model, numerical simulations were compared with the existing experimental data. The results are found in good agreement with the literature data. After validation of the numerical strategy, the axial velocity distribution and the anisotropy of the Reynolds stresses at several downstream longitudinal locations were obtained in order to investigate the hydrodynamic developments of the analyzed flow. The results show that in the ribbed bend pipe, the maximum velocity value is approximately 47% higher than the corresponding upstream value but it is 9% higher in the case of the bend pipe without ribs. It was also found for both cases that the distribution of the mean axial velocity depends faintly on the Dean number. Finally, it can be seen that the analyzed flow in the bend pipe without ribs appears more anisotropic than in bend pipe with ribs.

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