Hemodynamic impacts of hematocrit level by two-way coupled FSI in the left coronary bifurcation

2020 ◽  
Vol 76 (1) ◽  
pp. 9-26
Author(s):  
Saeed Bahrami ◽  
Mahmood Norouzi
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Blood Circulation ◽  
Arbitrary Lagrangian Eulerian ◽  
Coronary Bifurcation ◽  
Shear Rates ◽  
3D Geometry ◽  
Wall Shear ◽  
Rigid Walls

Cardiovascular disease is now under the influence of several factors that encourage researchers to investigate the flow of these vessels. Oscillation influences the blood circulation in the volume of red blood cells (RBC) strongly. Therefore, in this study, its effects have been considered on hemodynamic parameters in the elastic wall and coronary bifurcation. In this study, a 3D geometry of non-Newtonian and pulsatile blood circulation is considered in the left coronary artery bifurcation. The Casson model with various hematocrits is analyzed in elastic and rigid walls. The wall shear stress (WSS) cannot show the stenosis artery alone, therefore, the oscillatory shear index (OSI) is represented as a hemodynamic parameter of WSS individually of time. The results are determined using two-way fluid-structure interaction (FSI) coupling method using an arbitrary Lagrangian-Eulerian method. The most prominent difference in velocity happened in the bifurcation and at hematocrit 30 with yield stress 6.59E-04 Pa. The backflow and vortex flow in the LCx branch grown with increasing shear rates. The likelihood of plaque generation at the ending of the LM branch is observed in hematocrits 10 and 20, while the WSS magnitude is normal in the hematocrit 60 with the greatest yield stress in the bifurcation. The shear stress among the rigid and elastic models is the highest at the ending of the LM branch. The wall shear stress magnitude among the models decreased at most of 24.49% by dividing the flow. Time-independent results for models showed that there is the highest value of OSI at the bifurcation, which then quickly dropped.

scholarly journals Pipe rheology of microfibrillated cellulose suspensions

Cellulose ◽  
2019 ◽  
Vol 27 (1) ◽  
pp. 141-156 ◽  
Author(s):  
Tuomas Turpeinen ◽  
Ari Jäsberg ◽  
Sanna Haavisto ◽  
Johanna Liukkonen ◽  
Juha Salmela ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Power Law ◽  
Slip Flow ◽  
Microfibrillated Cellulose ◽  
Flow Index ◽  
Shear Rheology ◽  
Power Law Fluids ◽  
Wall Shear

Abstract The shear rheology of two mechanically manufactured microfibrillated cellulose (MFC) suspensions was studied in a consistency range of 0.2–2.0% with a pipe rheometer combined with ultrasound velocity profiling. The MFC suspensions behaved at all consistencies as shear thinning power law fluids. Despite their significantly different particle size, the viscous behavior of the suspensions was quantitatively similar. For both suspensions, the dependence of yield stress and the consistency index on consistency was a power law with an exponent of 2.4, similar to some pulp suspensions. The dependence of flow index on consistency was also a power law, with an exponent of − 0.36. The slip flow was very strong for both MFCs and contributed up to 95% to the flow rate. When wall shear stress exceeded two times the yield stress, slip flow caused drag reduction with consistencies higher than 0.8%. When inspecting the slip velocities of both suspensions as a function of wall shear stress scaled with the yield stress, a good data collapse was obtained. The observed similarities in the shear rheology of both the MFC suspensions and the similar behavior of some pulp fiber suspensions suggests that the shear rheology of MFC suspensions might be more universal than has previously been realized.

Non-Newtonian Flow Behavior in Microchannels for Emulsion Formation

2006 ◽  
Author(s):  
Ravi Arora ◽  
Eric Daymo ◽  
Anna Lee Tonkovich ◽  
Laura Silva ◽  
Rick Stevenson ◽  
...  
Keyword(s):  
Shear Stress ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Power Law ◽  
Flow Behavior ◽  
Scale Up ◽  
High Wall Shear Stress ◽  
Shear Rates ◽  
Wall Shear ◽  
Low Shear

Emulsion formation within microchannels enables smaller mean droplet sizes for new commercial applications such as personal care, medical, and food products among others. When operated at a high flow rate per channel, the resulting emulsion mixture creates a high wall shear stress along the walls of the narrow microchannel. This high fluid-wall shear stress of continuous phase material past a dispersed phase, introduced through a permeable wall, enables the formation of small emulsion droplets — one drop at a time. A challenge to the scale-up of this technology has been to understand the behavior of non-Newtonian fluids under high wall shear stress. A further complication has been the change in fluid properties with composition along the length of the microchannel as the emulsion is formed. Many of the predictive models for non-Newtonian emulsion fluids were derived at low shear rates and have shown excellent agreement between predictions and experiments. The power law relationship for non-Newtonian emulsions obtained at low shear rates breaks down under the high shear environment created by high throughputs in small microchannels. The small dimensions create higher velocity gradients at the wall, resulting in larger apparent viscosity. Extrapolation of the power law obtained in low shear environment may lead to under-predictions of pressure drop in microchannels. This work describes the results of a shear-thinning fluid that generates larger pressure drop in a high-wall shear stress microchannel environment than predicted from traditional correlations.

scholarly journals Effects of Surface Tension and Yield Stress on Mucus Plug Rupture: A Numerical Study

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yingying Hu ◽  
Francesco Romanò ◽  
James B. Grotberg
Keyword(s):  
Surface Tension ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Pressure Difference ◽  
Rupture Process ◽  
Viscoplastic Fluid ◽  
Air Interface ◽  
Mucus Plug ◽  
Wall Shear

Abstract We study the effects of surface tension and yield stress on mucus plug rupture. A three-dimensional simplified configuration is employed to simulate mucus plug rupture in a collapsed lung airway of the tenth generation. The Herschel–Bulkley model is used to take into account the non-Newtonian viscoplastic fluid properties of mucus. Results show that the maximum wall shear stress greatly changes right prior to the rupture of the mucus plug. The surface tension influences mainly the late stage of the rupture process when the plug deforms greatly and the curvature of the mucus–air interface becomes significant. High surface tension increases the wall shear stress and the time needed to rupture since it produces a resistance to the rupture, as well as strong stress and velocity gradients across the mucus–air interface. The yield stress effects are pronounced mainly at the beginning. High yield stress makes the plug take a long time to yield and slows down the whole rupture process. When the effects induced by the surface tension and yield forces are comparable, dynamical quantities strongly depend on the ratio of the two forces. The pressure difference (the only driving in the study) contributes to wall shear stress much more than yield stress and surface tension per unit length. Wall shear stress is less sensitive to the variation in yield stress than that in surface tension. In general, wall shear stress can be effectively reduced by the smaller pressure difference and surface tension.

The Impact of Hemorheology on Wall Shear Stress in a Separated and Reattached Flow Region

2013 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Flow Region ◽  
Shear Thinning ◽  
Progression Rate ◽  
Vortex Center ◽  
Wall Shear ◽  
Separated And Reattached Flow ◽  
The Impact

Wall-bounded separating and reattaching flows are encountered in biological applications dealing with blood flows through arteries and prosthetic devices. Separated and reattached flow regions have been associated in the past with the most common arterial disease, atherosclerosis. Previous studies suggest that local wall shear stress (WSS) patterns affect the location and progression rate of atherosclerotic lesions. A parametric study is performed to investigate the influence of hemorheology on the wall shear stress distribution in a separated and reattached flow region. Recent hemorheological studies quantified and emphasized the yield stress and shear-thinning non-Newtonian characteristics of unadulterated human blood. Numerical solutions to the governing equations that account for yield stress and shear-thinning rheological effects are obtained. A low WSS region is observed around the flow reattachment point while a peak WSS always exists close to the vortex center. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

scholarly journals Sensitivity Analysis of a Wall Boundary Condition for the Turbulent Pipe Flow of Herschel–Bulkley Fluids

Water ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 19 ◽  
Author(s):  
Dhruv Mehta ◽  
Adithya Thota Radhakrishnan ◽  
Jules van Lier ◽  
Francois Clemens
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Velocity ◽  
Yield Stress ◽  
Pressure Loss ◽  
Rheological Parameters ◽  
Relative Reduction ◽  
Wall Function ◽  
Wall Shear ◽  
Behaviour Index

This article follows from a previous study by the authors on the computational fluid dynamics-based analysis of Herschel–Bulkley fluids in a pipe-bounded turbulent flow. The study aims to propose a numerical method that could support engineering processes involving the design and implementation of a waste water transport system, for concentrated domestic slurry. Concentrated domestic slurry results from the reduction in the amount of water used in domestic activities (and also the separation of black and grey water). This primarily saves water and also increases the concentration of nutrients and biomass in the slurry, facilitating efficient recovery. Experiments revealed that upon concentration, domestic slurry flows as a non-Newtonian fluid of the Herschel–Bulkley type. An analytical solution for the laminar transport of such a fluid is available in literature. However, a similar solution for the turbulent transport of a Herschel–Bulkley fluid is unavailable, which prompted the development of an appropriate wall function to aid the analysis of such flows. The wall function (called ψ 1 hereafter) was developed using Launder and Spalding’s standard wall function as a guide and was validated against a range of experimental test-cases, with positive results. ψ 1 is assessed for its sensitivity to rheological parameters, namely the yield stress, the fluid consistency index and the behaviour index and their impact on the accuracy with which ψ 1 can correctly quantify the pressure loss through a pipe. This is done while simulating the flow of concentrated domestic slurry using the Reynolds-Averaged Navier–Stokes (RANS) approach for turbulent flows. This serves to establish an operational envelope in terms of the rheological parameters and the average flow velocity within which ψ 1 is a must for accuracy. One observes that, regardless of the fluid behaviour index, ψ 1 is necessary to ensure accuracy with RANS models only in flow regimes where the wall shear stress is comparable to the yield stress within an order of magnitude. This is also the regime within which the concentrated slurry analysed as part of this research flows, making ψ 1 a requirement. In addition, when the wall shear stress exceeds the yield stress by more than one order (either due to an inherent lower yield stress or a high flow velocity), the regular Newtonian wall function proposed by Launder and Spalding is sufficient for an accurate estimate of the pressure loss, owing to the relative reduction in non-Newtonian viscosity as compared to the turbulent viscosity.

Steady motion of Bingham liquid plugs in two-dimensional channels

2011 ◽  
Vol 705 ◽  
pp. 258-279 ◽  
Author(s):  
Parsa Zamankhan ◽  
Brian T. Helenbrook ◽  
Shuichi Takayama ◽  
James B. Grotberg
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Stress Gradient ◽  
Core Region ◽  
Driving Pressure ◽  
Two Dimensional ◽  
Airway Epithelial ◽  
The Core ◽  
Wall Shear

AbstractWe study numerically the steady creeping motion of Bingham liquid plugs in two-dimensional channels as a model of mucus behaviour during airway reopening in pulmonary airways. In addition to flow analysis related to propagation of the plug, the stress distribution on the wall is studied for better understanding of potential airway epithelial cell injury mechanisms. The yield stress behaviour of the fluid was implemented through a regularized constitutive equation. The capillary number, $\mathit{Ca}$, and the Bingham number, $\mathit{Bn}$, which is the ratio of the yield stress to a characteristic viscous stress, varied over the ranges 0.025–0.1 and 0–1.5, respectively. For the range of parameters studied, it was found that, while the yield stress reduces the magnitude of the shearing along the wall, it can magnify the amplitude of the wall shear stress gradient significantly, and also it can elevate the magnitude of the wall shear stress and wall pressure gradient up to 30 % and 15 %, respectively. Therefore, the motion of mucus plugs can be more damaging to the airway epithelial cells due to the yield stress properties of mucus. The yield stress also modifies the profile of the plug where the amplitude of the capillary waves at the leading meniscus decreases with increase in $\mathit{Bn}$. Other findings are that: the thickness of the static film increases with increasing $\mathit{Bn}$; the driving pressure difference increases linearly with $\mathit{Bn}$; and increasing $\mathit{Bn}$ extends any wall stagnation point beneath the leading meniscus to an unyielded line segment beneath the leading meniscus. With an increase in $\mathit{Bn}$, the unyielded areas appear and grow in the adjacent wall film as well as the core region of the plug between the two menisci. The plug length, ${L}_{P} $, mostly modifies the topology of the yield surfaces. It was found that the unyielded area in the core region between the two menisci grows as the plug length decreases. The very short Bingham plug behaves like a solid lamella. In all computed liquid plugs moving steadily, the von Mises stress attains its maximum value near the interface of the leading meniscus in the transition region. For Bingham plugs moving very slowly, $\mathit{Ca}\ensuremath{\rightarrow} 0$, the driving pressure is non-zero.

scholarly journals Comparison of Near-Wall Hemodynamic Parameters in Stented Artery Models

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Nandini Duraiswamy ◽  
Richard T. Schoephoerster ◽  
James E. Moore
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Solid Mechanics ◽  
Flow Characteristics ◽  
Separation Parameter ◽  
Wall Shear ◽  
Dynamics Simulations ◽  
Rigid Walls ◽  
Near Wall

Four commercially available stent designs (two balloon expandable—Bx Velocity and NIR, and two self-expanding—Wallstent and Aurora) were modeled to compare the near-wall flow characteristics of stented arteries using computational fluid dynamics simulations under pulsatile flow conditions. A flat rectangular stented vessel model was constructed and simulations were carried out using rigid walls and sinusoidal velocity input (nominal wall shear stress of 10±5 dyn/cm2). Mesh independence was determined from convergence (<10%) of the axial wall shear stress (WSS) along the length of the stented model. The flow disturbance was characterized and quantified by the distributions of axial and transverse WSS, WSS gradients, and flow separation parameters. Normalized time-averaged effective WSS during the flow cycle was the smallest for the Wallstent (2.9 dyn/cm2) compared with the others (5.8 dyn/cm2 for the Bx Velocity stent, 5.0 dyn/cm2 for the Aurora stent, and 5.3 dyn/cm2 for the NIR stent). Regions of low mean WSS (<5 dyn/cm2) and elevated WSS gradients (>20 dyn/cm3) were also the largest for the Wallstent compared with the others. WSS gradients were the largest near the struts and remained distinctly nonzero for most of the region between the struts for all stent designs. Fully recirculating regions (as determined by separation parameter) were the largest for the Bx Velocity stent compared with the others. The most hemodynamically favorable stents from our computational analysis were the Bx Velocity and NIR stents, which were slotted-tube balloon-expandable designs. Since clinical data indicate lower restenosis rates for the Bx Velocity and NIR stents compared with the Wallstent, our data suggest that near-wall hemodynamics may predict some aspects of in vivo performance. Further consideration of biomechanics, including solid mechanics, in stent design is warranted.

Inflow Conditions and the Wall Shear Stress Characteristics of a Biofluid in Separated and Reattached Flow Regions

2014 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Human Blood ◽  
Flow Separation ◽  
Shear Thinning ◽  
Vortex Center ◽  
Wall Shear ◽  
Separated And Reattached Flow ◽  
Inflow Conditions

The influence of inflow conditions and human blood rheology on the wall shear stress distribution in a confined separated and reattached flow region is investigated. The governing mass and momentum conservation equations along with the Herschel-Bulkley rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of uniform and fully-developed inflow velocity profiles on the wall shear stress (WSS) characteristics using hemorheological models that account for the yield stress and shear-thinning non-Newtonian characteristics of human blood. The highest WSS or WSSmax, is always observed inside the flow separation region at a location corresponding to that of the corner vortex center. Uniform inflow results in higher WSSmax values in comparison with fully-developed inflow for moderate upstream flow restrictions. The opposite trend is observed for severe flow restrictions. Uniform inflow always results in smaller flow separation regions and WSSmax values at locations closer to the flow restriction plane. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

Laminar-Turbulent Transition Flows of Non-Newtonian Slurries: Models Assessment

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Kofi Freeman K. Adane ◽  
Martin Agelin-Chaab
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Stress Ratio ◽  
Rheological Parameters ◽  
Transition Model ◽  
Flow Conditions ◽  
Wide Range ◽  
Engineering Models ◽  
Wall Shear

In this study, a qualitative assessment of transitional velocity engineering models for predicting non-Newtonian slurry flows in a horizontal pipe was performed using data from a wide range of pipe diameters (25–268 mm). In addition, the gamma theta transition model was used to compute selected flow conditions. These models were used to predict transitional velocities in large pipe diameters (up to 420 mm) for slurries. In general, it was observed that most of the current engineering models predict transitional velocities conservatively. Based on the gamma theta transition model results, for large Hedström numbers (He ≳ 105), other methods should be used to predict transitional velocities if a change in the pipe diameter (scale-up) results in an order of magnitude increase in the He value. It was also found that the gamma theta transition model predicted a laminar flow condition in the fully developed region for flow conditions with a small plug region (low-yield stress-to-wall shear stress ratio), which is contrary to what has been observed in some experiments. This is attributed to the local fluid rheological parameters values, which might be different from those reported. However, the gamma theta transition model results are in good agreement with the experimental data for flow conditions that have a large plug region (high-yield stress-to-wall shear stress ratio).

FSI SIMULATION OF A HEALTHY CORONARY BIFURCATION FOR STUDYING THE MECHANICAL STIMULI OF ENDOTHELIAL CELLS UNDER DIFFERENT PHYSIOLOGICAL CONDITIONS

2015 ◽  
Vol 15 (05) ◽  
pp. 1550089 ◽  
Author(s):  
HOSSEIN ALI PAKRAVAN ◽  
MOHAMMAD SAID SAIDI ◽  
BAHAR FIROOZABADI
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Direction ◽  
Mechanical Stimuli ◽  
Coronary Bifurcation ◽  
Physiological Conditions ◽  
Atherosclerotic Lesions ◽  
Wall Shear ◽  
And Function

Atherosclerosis is a world-spread and well-known disease. This disease strongly relates to the endothelial cells (ECs) function. Normally, the endothelial cells align in the flow direction in the atheroprotected sites; however, in the case of atheroprone sites these cells orient randomly. The mechanical stimuli such as wall shear stress and strains could determine the morphology and function of the endothelial cells. In the present study, we numerically simulated the left main coronary artery (LCA) and its branches to left anterior descending (LAD) and left circumflex coronary (LCX) artery using fluid–structure interaction (FSI) modeling. The results were presented as longitudinal and circumferential strains of ECs as well as wall shear stress. Wide ranges of heart rate, cardiac motion, systolic and diastolic pressures were considered and their effects on mechanical stimuli were described in detail. The results showed that these factors could greatly influence the risk of atherosclerosis and the location of atherosclerotic lesions.

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