Pulsatile Non-Newtonian Flow Characteristics in a Three-Dimensional Human Carotid Bifurcation Model

1991 ◽  
Vol 113 (4) ◽  
pp. 464-475 ◽  
Author(s):  
K. Perktold ◽  
M. Resch ◽  
H. Florian
Keyword(s):  
Shear Stress ◽  
Carotid Sinus ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Outer Wall ◽  
Maximum Diameter ◽  
Newtonian Flow ◽  
Pulse Cycle ◽  
Flow Phenomena ◽  
Human Carotid

Numerical analysis of flow phenomena and wall shear stresses in the human carotid artery bifurcation has been carried out using a three-dimensional geometrical model. The primary aim of this study is the detailed discussion of non-Newtonian flow velocity and wall shear stress during the pulse cycle. A comparison of non-Newtonian and Newtonian results is also presented. The applied non-Newtonian behavior of blood is based on measured dynamic viscosity. In the foreground of discussion are the flow characteristics in the carotid sinus. The investigation shows complex flow patterns especially in the carotid sinus where flow separation occurs at the outer wall throughout the systolic deceleration phase. The changing sign of the velocity near the outer sinus wall results in oscillating shear stress during the pulse cycle. At the outer wall of the sinus at maximum diameter level the shear stress ranges from −1.92 N/m2 to 1.22 N/m2 with a time-averaged value of 0.04 N/m2. At the inner wall of the sinus at maximum diameter level the shear stress range is from 1.16 N/m2 to 4.18 N/m2 with a mean of 1.97 N/m2. The comparison of non-Newtonian and Newtonian results indicates unchanged flow phenomena and rather minor differences in the basic flow characteristics.

scholarly journals PIV Investigation of the Flow Characteristics in an Internal Coolant Passage With 45deg Rib Arrangement

1999 ◽  
Author(s):  
J. Schabacker ◽  
A. Boelcs ◽  
B. V. Johnson
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Outer Wall ◽  
Secondary Flows ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Working Medium ◽  
Staggered Arrangement ◽  
Flow Phenomena ◽  
Rib Arrangement

Flow characteristics in a model of a stationary two-pass internal coolant passage were measured with the stereoscopic PIV technique. From the PIV measurements, the 3D mean velocity field and turbulence quantities of the flow were obtained simultaneously with high spatial resolution, which allowed for an understanding of the flow phenomena in the coolant passage. The model of the coolant passage consists of two square legs, each having a length of 19 hydraulic diameters that are connected by a sharp 180deg bend with a rectangular outer wall. In the two legs, 45deg ribs are mounted in a staggered arrangement on the bottom and top wall, with rib heights equal to 0.1 hydraulic diameter, and rib spacing of 10 rib heights. The measurements were carried out for a Reynolds number of 45,700 with air as working medium. The paper presents results of the flow development in the straight legs of the passage and in the bend. The oblique ribs in the straight legs contribute to the development of secondary flows that transport fluid from the leg center towards the walls. In the bend of the passage, the interaction between rib-induced and bend-induced secondary flows leads to a three-dimensional flow. Downstream of the bend, the ribs quickly dominate the flow and thus lead to a fast recovery of the flow from the bend effect.

scholarly journals Flow-Induced Vibration on the Control Valve with a Different Concave Plug Shape Using FSI Simulation

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Akram Zeid ◽  
Mohamed Shouman
Keyword(s):  
High Efficiency ◽  
Complex Structure ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
Control Valve ◽  
Low Noise ◽  
Flow Induced Vibration ◽  
Nonlinear Characteristics ◽  
Flow Phenomena

Control valves have always been recognised as being among the most crucial control equipment, commonly utilised in versatile engineering applications. Hence, the need has arisen to identify the flow characteristics inside the valve, together with the incurred vibration induced as a result of the flow passing through the valve. Thanks to the tangible and fast progress made in the field of the flow simulation and numerical techniques, it has become possible to better observe the behavior of the flow passing inside a valve with view to examining its performance. Hence, the paper at hand is mainly concerned with introducing the modeling and simulation of a control valve. On the contrary, the flow system in a control valve is marked by a complex structure and nonlinear characteristics. The reasons for those qualities could be attributed to its construction as well as the fluid flow phenomena associated with it. It is especially for the sake of investigating and observing the flow characteristics, pertaining to a control valve equipped with different concave plug shapes and different openings, that the three-dimensional FSI simulation is conducted. In addition, it would be possible to make use of the obtained results relating to the three-dimensional analysis to achieve low noise and high efficiency improvement. Furthermore, all results will be validated on experimental grounds.

scholarly journals Three-Dimensional Flow Characteristics in Slit-Type Permeable Spur Dike Fields: Efficacy in Riverbank Protection

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 964 ◽  
Author(s):  
Shampa ◽  
Yuji Hasegawa ◽  
Hajime Nakagawa ◽  
Hiroshi Takebayashi ◽  
Kenji Kawaike
Keyword(s):  
Shear Stress ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Efficient Solutions ◽  
Staggered Grid ◽  
Bed Shear Stress ◽  
Experimental Conditions ◽  
Alluvial Rivers ◽  
Spur Dike

This paper focuses on finding efficient solutions for the design of a highly permeable pile spur (or slit type) dike field used in morphologically dynamic alluvial rivers. To test the suitability of different arrangements of this type of permeable pile spur dike field, laboratory experiments were conducted, and a three-dimensional multiphase numerical model was developed and applied, based on the experimental conditions. Three different angles to the approach flow and two types of individual pile position arrangements were tested. The results show that by using a series of slit-type spurs, the approach velocity of the flow can be considerably reduced within the spur dike zone. Using different sets of angles and installation positions, this type of permeable spur dike can be used more efficiently than traditional dikes. Notably, this type of spur dike can reduce the longitudinal velocity, turbulence intensity, and bed shear stress in the near-bank area. Additionally, the deflection of the permeable spur produces more transverse flow to the opposite bank. Arranging the piles in staggered grid positions among different spurs in a spur dike field improves functionality in terms of creating a quasi-uniform turbulence zone while simultaneously reducing the bed shear stress. Finally, the efficacy of the slit-type permeable spur dike field as a solution to the riverbank erosion problem is numerically tested in a reach of a braided river, the Brahmaputra–Jamuna River, and a comparison is made with a conventional spur dike field. The results indicate that the proposed structure ensures the smooth passing of flow compared with that for the conventional impermeable spur structure by producing a lower level of scouring (low bed shear stress) and flow intensification.

Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Yunfei Xing ◽  
Fengquan Zhong ◽  
Xinyu Zhang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Outer Wall ◽  
Centrifugal Effect

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k–ω turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

A Parametric Study on Fatigue Life for Mixed Elastohydrodynamic Lubrication Point Contacts

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Xiao-Liang Yan ◽  
Xiao-Li Wang ◽  
Yu-Yan Zhang
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Newtonian Flow ◽  
Lubrication Regimes ◽  
Close Relationship ◽  
Lubrication Characteristics ◽  
Effect Of Surface

The lubrication characteristics and fatigue life are numerically analyzed under full film and mixed lubrication regimes, in which the three-dimensional sinusoidal surfaces with changeable wavelengths in x and y directions are used, the geometry changes of the contact areas are described by the various ellipticity, and the non-Newtonian flow of lubricant is described by the sinh-law rheology model. The results show that the influences of characteristic shear stress, wavelength ratio, and ellipticity on lubrication characteristics and fatigue life are remarkable. The effect of surface topography on lubrication characteristics has a close relationship with speed. Increasing the ellipticity and decreasing wavelength ratio and characteristic shear stress can prolong the fatigue life.

Non-Newtonian Flow Over a Wedge With Injection or Suction

1991 ◽  
Author(s):  
Vijay K. Garg
Keyword(s):  
Differential Equation ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Incompressible Fluid ◽  
Wedge Angle ◽  
Flow Characteristics ◽  
Second Grade ◽  
Newtonian Flow ◽  
Linear Differential ◽  
Blowing Parameter

Abstract A pseudo-similarity solution is obtained for the flow of an incompressible fluid of second grade past a wedge with suction or blowing at the surface. The non-linear differential equation is solved using quasi-linearization and orthonormalization. The numerical method developed for this purpose enables computation of the flow characteristics for any value of the parameters K, a, and b, where K is the dimensionless normal stress modulus of the fluid, a is related to the wedge angle, and b is the suction or blowing parameter. A significant effect of suction or blowing on the wall shear stress is observed. The present results match exactly with those from an earlier perturbation analysis for Kx2a ≤ 0.01 but differ significantly as Kx2a increases.

Flow Characteristics in an Airlift Membrane Bioreactor

2009 ◽  
Vol 4 (5) ◽  
Author(s):  
Amirhossein Khalili ◽  
MR Mehrnia ◽  
Navid Mostoufi ◽  
Mohammad Sarrafzadeh
Keyword(s):  
Shear Stress ◽  
Membrane Bioreactor ◽  
Fluid Model ◽  
Membrane Surface ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Liquid Level ◽  
Two Fluid Model ◽  
Two Fluid

Effect of changing the liquid level in an airlift membrane bioreactor of 0.7 m height, 0.24 m width and 0.18 m depth was studied both experimentally and by simulation. Three-dimensional simulations of the airlift membrane bioreactor were carried out at two different liquid levels above the membrane. The simulations were based on the two-fluid model with the standard k–? model for the turbulence. The results showed that by lowering the liquid level, the quality of mixing and uniformity of the velocity distribution of liquid phase in the riser would be improved while the shear stress on the membrane surface would be reduced. Higher shear stress on the membrane surface at high levels of liquid minimizes the extent to which particles settle on the membrane, thus, fouling will be reduced and flux of liquid through membrane will be enhanced. Moreover, it was shown that by lowering the liquid level, the fraction of air in the downcomers becomes lower.

Numerical Studies of Three-Dimensional Arterial Flows in Reverse Curvature Geometry: Part I—Peak Flow

1993 ◽  
Vol 115 (3) ◽  
pp. 316-326 ◽  
Author(s):  
R. K. Banerjee ◽  
Y. I. Cho ◽  
L. H. Back
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Outer Wall ◽  
Momentum Effect ◽  
Centrifugal Effect ◽  
Stress Region ◽  
Secondary Motion ◽  
Low Shear Stress ◽  
Experimental Values

A three-dimensional flow simulation at Repeak = 192 and 580 was made in a smooth reverse curvature model that conformed to the gentle “S” shape from a human left femoral artery angiogram. The objective of this numerical investigation was to find the changes in pressure, shear stress, velocity profile, and particle path occurring in the double-curved arterial vessel. Due to the impingement of blood at the outer wall in the first bend region, the wall shear stress approached 40 dyne/cm2—a value over twice as large as in the straight upstream segment. Conversely, at the inner wall in the first bend, a low shear stress region was found where the value of the shear stress was consistently smaller than that in the straight section. The initiation of centrifugal effects caused by the first bend could clearly be seen at Repeak = 580, but due to the close proximity of the reverse curvature segment, the momentum effect due to the second bend overshadowed the centrifugal effect. Hence, only near the end of the second bend did the centrifugal effect due to the second bend result in a double-spiral-secondary motion. In addition, the numerically calculated pressure drop data were in agreement with prior experimental values.

scholarly journals Effects of size and elasticity on the relation between flow velocity and wall shear stress in side-wall aneurysms: A lattice Boltzmann-based computer simulation study

2019 ◽  
Author(s):  
Haifeng Wang ◽  
Timm Krüger ◽  
Fathollah Varnik
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Velocity ◽  
Lattice Boltzmann ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Side Wall ◽  
Aneurysm Rupture ◽  
Immersed Boundary ◽  
Wall Shear

AbstractBlood flow in an artery is a fluid-structure interaction problem. It is widely accepted that aneurysm formation, enlargement and failure are associated with wall shear stress (WSS) which is exerted by flowing blood on the aneurysmal wall. To date, the combined effect of aneurysm size and wall elasticity on intra-aneurysm (IA) flow characteristics, particularly in the case of side-wall aneurysms, is poorly understood. Here we propose a model of three-dimensional viscous flow in a compliant artery containing an aneurysm by employing the immersed boundary-lattice Boltzmann-finite element method. This model allows to adequately account for the elastic deformation of both the blood vessel and aneurysm walls. Using this model, we perform a detailed investigation of the flow through aneurysm under different conditions with a focus on the parameters which may influence the wall shear stress. Most importantly, it is shown in this work that the use of flow velocity as a proxy for wall shear stress is well justified only in those sections of the vessel which are close to the ideal cylindrical geometry. Within the aneurysm domain, however, the correlation between wall shear stress and flow velocity is largely lost due to the complexity of the geometry and the resulting flow pattern. Moreover, the correlations weaken further with the phase shift between flow velocity and transmural pressure. These findings have important implications for medical applications since wall shear stress is believed to play a crucial role in aneurysm rupture.

scholarly journals Effect of Sinuosity on Shear Stress Distribution in Meandering Channel

2019 ◽  
Vol 9 (1) ◽  
pp. 219-226
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Flow Characteristics ◽  
Outer Wall ◽  
Shear Stress Distribution ◽  
Natural Phenomenon ◽  
Large Eddy Simulation Model ◽  
Meandering Channel ◽  
Meandering Channels ◽  
Percentage Difference

Rivers have always been the lifelines of the civilizations and meandering is a well known natural phenomenon in which a river deviates from its straight path and form a curvature of reverse order. To study the flow characteristics of a meandering river understanding of shear stress distribution in a meander section is of immense importance. Shear stress distribution in a meandering section depends upon various factors like shape of cross section, slope and hydraulic radius etc. Among all these factors sinuosity is a crucial factor which affect the shear stress distribution in a meandering section. This research put forward the effect of variation in sinuosity on shear stress distribution.CFD(Computational Flow Dynamics) analysis is adopted over experimental work due to its reliability and accuracy. ANSYS 18.1 is used for the simulation of meandering channels. In this research we design three meandering channels with sinuosity values 1.47, 2.0 and 2.53. Each model is simulated for three different values of discharge i.e. 1,2 and 3 cumec. Hence a total of 9 models are created for the analysis. Meshing is done for the domain and its accuracy is examined by performing grid independence study. LES(Large Eddy Simulation) model is used to incorporate turbulence in the model. This model is chosen due to its better efficiency and accuracy over others in open channel simulations. The results show that shear stress on inner wall of meandering channel is more than that on outer wall. Velocity profiles are found to be in agreement with shear stress distribution. Percentage difference between inner and outer wall shear stress values decreases as we increase the sinuosity.

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