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.

Evaluation of Slip Effects in the Capillary Flow of Foams

1999 ◽  
Vol 9 (1) ◽  
pp. 10-16 ◽  
Author(s):  
Karim Bekkour
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Slip Velocity ◽  
Capillary Flow ◽  
Strong Dependence ◽  
Sodium Dodecyl ◽  
Wall Slip ◽  
Reynolds Analogy ◽  
Slip Effects ◽  
Wall Shear

Abstract Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

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.

WALL SLIP EFFECTS MEASURING THE RHEOLOGICAL BEHAVIOR OF ELECTRORHEOLOGICAL (ER) SUSPENSIONS

2012 ◽  
Vol 26 (01) ◽  
pp. 1250006 ◽  
Author(s):  
STEFFEN SCHNEIDER
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Behavior ◽  
Wall Slip ◽  
Hydraulic Test ◽  
Slip Effects ◽  
Measured Flow ◽  
Wall Shear ◽  
Er Fluids ◽  
Electrorheological Suspensions

In this work, a new method to determine the wall shear stress was developed step by step. To determine the wall shear stress, methods of the suspension rheology are being used for the first time to characterize ER fluids. This work focuses on investigations of the flow behavior of electrorheological suspensions in flow channels with different geometries at different electrical field strengths. Careful interpretation of the results with respect to different gap geometries has shown that the measured flow curves should undergo a combination of corrections. As a result it can be shown that wall slip effects can be measured under application like conditions on a hydraulic test bench.

Compaction and flow of potato starch and potato granules Compactación y flujo de almidón de patata y gránulos de patata

1997 ◽  
Vol 3 (5) ◽  
pp. 333-342 ◽  
Author(s):  
P.J. Halliday ◽  
A.C. Smith
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Water Content ◽  
Capillary Flow ◽  
Potato Starch ◽  
Slip Flow ◽  
Shear Stresses ◽  
Wall Shear ◽  
Water Contents

Potato starch and potato granules are materials that are often used in extrusion processes. It is important to quantify their rheology for modelling and prediction of process performance. The compaction behaviour of potato starch was examined at water contents of 4-18% wwb (wet weight basis) for pressures between 1 and 85 MPa. The Heckel deformation stress decreased as the water content increased up to 12% but became inaccurate at 18%. This decrease agreed qualitatively with other observations of the decrease in stiffness of starchy materials over this water content range. Potato granules were examined at water contents of 25-45% wwb and aspects of their rheo logical behaviour characterized using different approaches. A first approximation used the shear viscosity-shear rate power law which produced a law exponent for the resulting pastes (0.1-0.2). The classical Benbow equation was used to estimate yield and wall shear stresses in capillary flow. The latter indicates the presence of slip which was examined more fully as a function of wall shear stress. The Mooney technique was used together with a variation of the method where the shear rate for each die was subtracted from that for a non-slip flow, which was approximated using rough dies. A critical wall shear stress for slip was found to be 0.05-0.1 MPa, making it consistent with published results for other materials.

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.

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.

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