Comments on the paper by Y-H. Wu and K-F Liu : Start-up flow of a Bingham fluid between coaxial cylinders under a constant wall shear stress journal of non-Newtonian fluid mechanics 223 (2015), 116–121

2017 ◽  
Vol 244 ◽  
pp. 42-43 ◽  
Author(s):  
R.R. Huilgol
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Mechanics ◽  
Newtonian Fluid ◽  
Bingham Fluid ◽  
Coaxial Cylinders ◽  
Start Up ◽  
Wall Shear

Accurate Prediction of Wall Shear Stress in a Stented Artery: Newtonian Versus Non-Newtonian Models

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Juan Mejia ◽  
Rosaire Mongrain ◽  
Olivier F. Bertrand
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Linear Model ◽  
Newtonian Fluid ◽  
Nonlinear Model ◽  
Numerical Models ◽  
Neointimal Hyperplasia ◽  
Computational Cost ◽  
Arterial Segment ◽  
Wall Shear

A significant amount of evidence linking wall shear stress to neointimal hyperplasia has been reported in the literature. As a result, numerical and experimental models have been created to study the influence of stent design on wall shear stress. Traditionally, blood has been assumed to behave as a Newtonian fluid, but recently that assumption has been challenged. The use of a linear model; however, can reduce computational cost, and allow the use of Newtonian fluids (e.g., glycerine and water) instead of a blood analog fluid in an experimental setup. Therefore, it is of interest whether a linear model can be used to accurately predict the wall shear stress caused by a non-Newtonian fluid such as blood within a stented arterial segment. The present work compares the resulting wall shear stress obtained using two linear and one nonlinear model under the same flow waveform. All numerical models are fully three-dimensional, transient, and incorporate a realistic stent geometry. It is shown that traditional linear models (based on blood’s lowest viscosity limit, 3.5 Pa s) underestimate the wall shear stress within a stented arterial segment, which can lead to an overestimation of the risk of restenosis. The second linear model, which uses a characteristic viscosity (based on an average strain rate, 4.7 Pa s), results in higher wall shear stress levels, but which are still substantially below those of the nonlinear model. It is therefore shown that nonlinear models result in more accurate predictions of wall shear stress within a stented arterial segment.

scholarly journals Modeling Blood Pulsatile Turbulent Flow in Stenotic Coronary Arteries

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Newtonian Fluid ◽  
Coronary Arteries ◽  
Pathological Condition ◽  
Flow Behavior ◽  
Wall Shear ◽  
Stenotic Arteries

Atherosclerosis is a potentially serious illness where arteries become clogged with fatty substances called plaques. Over the years, this pathological condition has been deeply studied and computational fluid dynamics has played an important role in investigating the blood flow behavior. Commonly, the blood flow is assumed to be laminar and a Newtonian fluid. However, under a stenotic condition, the blood behaves as a non-Newtonian fluid and the pulsatile blood flow through coronary arteries could result in a transition from laminar to turbulent flow condition. The present study aims to analyze and compare numerically the blood flow behavior, applying the k-ω SST model and a laminar assumption. The effects of Newtonian and non-Newtonian (Carreau) models were also studied. In addition, the effect of the stenosis degree on velocity fields and wall shear stress based descriptors were evaluated. According to the results, the turbulent model is shown to give a better overall representation of pulsatile flow in stenotic arteries. Regarding, the effect of non-Newtonian modeling, it was found to be more significant in wall shear stress measurements than in velocity profiles. In addition, the appearance of recirculation zones in the 50% stenotic model was observed during systole, and a low TAWSS and high OSI were detected downstream of the stenosis which, in turn, are risk factors for plaque formation. Finally, the turbulence intensity measurements allowed to distinguish regions of recirculating and disturbed flow.

Numerical Study on Flow-Adaptive Stents

2008 ◽  
Vol 33-37 ◽  
pp. 1031-1036
Author(s):  
Yoko Takakura ◽  
Gulbahar Wahap ◽  
Norio Arai ◽  
Yoshifumi Konishi ◽  
Kazuaki Fukasaku
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Fluid Mechanics ◽  
Endovascular Therapy ◽  
Numerical Study ◽  
Two Dimensional ◽  
Numerical Computations ◽  
Wall Shear ◽  
Two Dimensional Flows

Recently for the treatment of aneurysms, endovascular therapy with microcoils and stents has started. This study explores the design of better stents by means of numerical computations from the viewpoint of the fluid mechanics. Two-dimensional flows are numerically solved for a stented duct with a model of an aneurysmal sac by changing the distribution of stent filaments under the constraint of a constant porosity for the neck. Stents are assessed by whether the wall shear stress (WSS) on the aneurismal wall and the shear rate (SR) within the aneurysm are made lower. Barometers for the allocation of filaments are sought, and resultant optimized stents are those where filament(s) should be attached to both the distal and proximal wall of the neck, with more filaments to the distal wall, to make the WSS low, and filaments should be appropriately distributed in the off-wall portion of the neck to make the SR low.

A 3D-LDA Study of the Relation Between Wall Shear Stress and Intimal Thickness in a Human Aortic Bifurcation

1996 ◽  
Vol 118 (3) ◽  
pp. 273-279 ◽  
Author(s):  
Kozaburo Hayashi ◽  
Yutaka Yanai ◽  
Takeru Naiki
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Blood Vessel ◽  
Newtonian Fluid ◽  
Shear Stresses ◽  
Elastic Model ◽  
Aortic Bifurcation ◽  
Local Flow ◽  
Intimal Thickness ◽  
Wall Shear

A realistic model experiment on hemodynamics was performed to study correlations between wall shear stresses measured in a cast model of the aortic bifurcation and intimal thickness at each corresponding site of the native blood vessel from which the cast had been made. An elastic model of a 54 year old human aortic bifurcation was made of a polyurethane elastomer using a dipping method, and was perfused with Newtonian or non-Newtonian fluid under physiologic pulsatile flow condition. Local flow velocities were measured with an optical-fibered, 3-dimensional laser Doppler anemometer (3D-LDA) to determine wall shear stresses. Distribution of intimal thickness was determined using histological specimens of the native blood vessel. The results obtained are: 1) Non-Newtonian fluid rheology increased wall shear stresses; 2) Positive correlations were observed between intimal thickness and the maximum instantaneous wall shear stress, and 3) However, if we take only the data from the circumference at the level of the flow divider tip, there were negative correlations between them.

scholarly journals Understanding the fluid mechanics behind transverse wall shear stress

2017 ◽  
Vol 50 ◽  
pp. 102-109 ◽  
Author(s):  
Yumnah Mohamied ◽  
Spencer J. Sherwin ◽  
Peter D. Weinberg
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Mechanics ◽  
Transverse Wall ◽  
Wall Shear

EFFECTS OF HEMATOCRIT LEVEL ON THE BLOOD FLOW IN THE CORRUGATED VESSEL DUE TO THE IMPLANTATION OF INTRAVASCULAR STENTS

2006 ◽  
Vol 18 (02) ◽  
pp. 80-86 ◽  
Author(s):  
TA-WEI DAVID TING ◽  
BING-SHIUN WU
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Stress Distribution ◽  
Wall Shear Stress ◽  
Newtonian Fluid ◽  
Shear Stress Distribution ◽  
Hematocrit Level ◽  
Wall Shear Stress Distribution ◽  
Atheroma Plaque ◽  
Wall Shear

The vascular stenting has been accepted as a very effective treatment of occlusive vascular disease. But the implantation of vascular stent will change the geometric shape of stenosed vessel to be corrugated and create some local hemodynamic features characterized by the flow separation, recirculation in the area close to the stent. Under the physiological conditions of left coronary artery and specific geometric shapes created by the implantation of stent, the numerical method has been used to solve the blood flow and the shear stress distribution patterns in the vicinity of the stent. The non-Newtonian fluids with different levels of hematocrit (H), 25%, 45%, 65% are employed for the numerical simulation and compared with the numerical results of the Newtonian fluid in which the blood viscosity is assumed to be constant. The simulations have revealed that the surface of stent and atheroma bumps experience lower time-averaged wall shear stress by the non-Newtonian fluid with lower level of hematocrit. The value of wall shear stress on the peak of atheroma bumps has also been studied because it may associate with the cause the rupture of atheroma plaque. The numerical results of Newtonian fluid were compared with those of non-Newtonian fluid with hematocrit level of 45%, the average hematocrit value inherent in normal person. It is noted that non-Newtonian effect on the time-averaged wall shear stress distribution along the stent surface is not significant. The outline of bulged atheroma experiences almost same time-averaged shear stress distribution acting by the fluid with or without the non-Newtonian property. It means that for the non-Newtonian fluid with hematocrit level of 45% the property of changing viscosity in the flow field didn't affect the results of wall shear stress distribution on the surfaces of stent and atheroma bump resulted from the simulation of Newtonian fluid flow. These results will provide insight into the effects of different levels of hematocrit on the blood flow in the corrugated vessel due to the implantation of stent. Our findings suggest that the level of hematocrit is closely associated with the value of wall shear stress distribution. It is particularly significant to acute stage of atherogenesis, intimal hyperplasia, platelet deposition, thrombosis, endothelial cell orientation and the rupture of atheroma plaque after the implantation of stent. Some of the results presented can be used to explain the clinical performance of vascular stenting.

Numerical Simulation of Fluid-Induced Vibration and Wall Shear Stress in Fusi/Form Cerebral Aneurysm: Newtonian and Non-Newtonian Fluid

2006 ◽  
Author(s):  
Yong Hyun Kim ◽  
Joon Sand Lee ◽  
Xin Wu
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Newtonian Fluid ◽  
Stress Gradient ◽  
In Vivo Studies ◽  
Rupture Area ◽  
Study Results ◽  
Wall Shear

Vascular techniques have been used for curing the aneurysm, but the reason for the occurrence of aneurysms can not be known using these techniques. These techniques are usually used for preventing a significant situation such as rupture of an aneurysm. In our study, blood flow effects with or without vascular techniques inside an aneurysm were analyzed with computational fluid dynamics (CFD). Important hemodynamic quantities like wall shear stress and pressure in vessel are difficult to measure in-vivo. Blood flow is assumed to be Newtonian fluid. But it actually consists of platelets, so it is also considered a non-Newtonian fluid in this study. Results of the numerical model were used to compare and analyze fluid characteristics with experimental data. Using the flow characteristics (wall shear stress (WSS), wall shear stress gradient (WSSG)), the rupture area was identified to be located in the distal area. However, the rupture area, in vivo studies, was observed to be present at a different location. During pulsatile flow, vibration induced by flow is implicated by weakening of the artery wall and affects more than shear stress. After adapting the fluid-induced vibration, the rupture area in aneurysm is found to be located in the same area as the in-vivo result. Since smaller inflow and low WSS provide the effect of the distal neck, the vibration provides more effects in dome area. In this study it has been found that the effect of shear stress on the rupture of aneurysm is less than the effect of vibration. In the case of non-Newtonian fluid, vibration induced by flow also has more effects than WSS and WSSG. The simulation results gave detailed information about hemodynamics under physiological pulsatile inlet condition.

Numerical Analysis of Wall Slip Effects on Flow of Newtonian and Non-Newtonian Fluids in Macro and Micro Contraction Channels

2006 ◽  
Vol 129 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Alfeus Sunarso ◽  
Takehiro Yamamoto ◽  
Noriyasu Mori
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Newtonian Fluid ◽  
Stress Function ◽  
Slip Velocity ◽  
Wall Slip ◽  
Average Shear ◽  
Wall Shear ◽  
Shear Stress Function

We performed numerical simulation to investigate the effects of wall slip on flow behaviors of Newtonian and non-Newtonian fluids in macro and micro contraction channels. The results show that the wall slip introduces different vortex growth for the flow in micro channel as compared to that in macro channel, which are qualitatively in agreement with experimental results. The effects of slip on bulk flow behaviors depend on rheological property of the fluid. For Newtonian fluid, the wall slip always reduces the vortex length, while for non-Newtonian fluid, the strength of the slip determines whether the vortex length is reduced or increased. Analyses on the velocity and stress fields confirm the channel size dependent phenomena, such as the reduction of wall shear stress with the decrease in channel size. With the increase in average shear rate, the Newtonian fluid shows the reduction of wall shear stress that increases in the same trend with slip velocity-wall shear stress function, while for non-Newtonian fluid, the effect of the slip is suppressed by shear thinning effect and, therefore, the reduction of wall shear stress is less sensitive to the change in average shear rate and slip velocity-wall shear stress function.

COUPLE STRESS FLUID MODEL FOR PULSATILE FLOW OF BLOOD IN A POROUS TAPERED ARTERIAL STENOSIS UNDER MAGNETIC FIELD AND PERIODIC BODY ACCELERATION

2017 ◽  
Vol 17 (08) ◽  
pp. 1750109 ◽  
Author(s):  
R. PONALAGUSAMY ◽  
S. PRIYADHARSHINI
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Newtonian Fluid ◽  
Couple Stress ◽  
Flow Resistance ◽  
Fluid Model ◽  
Arterial Stenosis ◽  
Couple Stress Fluid ◽  
Flow Through ◽  
Wall Shear

In this paper, a magnetic and non-Newtonian fluid model for pulsatile flow of blood with periodic body acceleration has been investigated by adopting Laplace transform and finite Hankel transform. A closed form of analytic solution is obtained for physiologically important quantities such as velocity profile, flow rate, wall shear stress and flow resistance. Effects of different physical parameters reflecting couple stress parameter, Darcy number, Hartman number, tapering angle (divergent tapered tube or convergent tapered tube), shape stenosis parameter and amplitude of periodic acceleration on wall shear stress and flow resistance have been emphasized. For any value of taper angle ([Formula: see text]) and stenotic height ([Formula: see text]), it is pertinent to point out here that the wall shear stress is less in the case of flow through the asymmetric stenosed tube as compared to the case of flow through the symmetric stenosed tube when one is in the up-stream of flow region, but it is of opposite behavior as one moves in the down-stream of flow region. It is important to note that the flow resistance increases significantly and more nonlinearly with the increase in the axial distance in the case of flow through a converging tapered artery with stenosis as compared to that of the same flow through a stenosed artery. The size of trapping bolus becomes larger for the flow of couple stress fluid through a converging tapered arterial stenosis than that of the same flow through a stenosed artery. Another important result is that as compared to the case of Newtonian fluid, the couple stress fluid behaviour plays a key role in increasing the size of trapping bolus. This investigation puts forward important observations that the asymmetric nature of stenosis considered plays a predominant role in reducing the flow resistance in the case of diseased blood vessel and the flow resistance is higher for the case of couple stress fluid than that of Newtonian fluid. Finally, some applications of the present model have been briefly discussed.

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