Numerical Analysis of Steady Flow in Aorto-Coronary Bypass 3-D Model

1996 ◽  
Vol 118 (2) ◽  
pp. 172-179 ◽  
Author(s):  
Fabio Inzoli ◽  
Francesco Migliavacca ◽  
Giancarlo Pennati
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Intimal Hyperplasia ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Coronary Bypass ◽  
Secondary Flows ◽  
Geometrical Parameters ◽  
Shear Stresses

Intimal hyperplasia and atherosclerosis have a predominant role in the failure of coronary artery bypass procedures. Theoretical studies and in vivo observations have shown that these pathologies are much more likely to occur in the proximity of end-to-side anastomosis, thus indicating that fluid dynamic conditions may be included in the pathogenic causes of the initiation, progression and complication of intimal hyperplasia. In order to study the fluid dynamics at the anastomosis of an aorto-coronary bypass, a three-dimensional mathematical model based on a FEM approach was developed. Steady-state simulations were studied in two different geometrical models of anastomosis which differ in their insertion angles (45 and 60 degree). Flow fields with three-dimensional helical patterns, secondary flows, and shear stresses were also investigated. The results show the presence of low shear stresses on the top wall just beyond the toe of the anastomosis and in the region of the coronary artery before the junction. A high wall shear stress region is present on the lateral wall of the coronary artery immediately downstream from the anastomosis. The influence of flow rate distribution on the secondary flows is also illustrated. These results confirm the sensitivity of flow behavior to the model’s geometrical parameters and enhance the importance of reproducing the anastomosis junction as closely as possible in order to evaluate the effective shear stress distribution.

Comparison of Left Anterior Descending Coronary Artery Hemodynamics Before and After Angioplasty

2005 ◽  
Vol 128 (1) ◽  
pp. 40-48 ◽  
Author(s):  
S. D. Ramaswamy ◽  
S. C. Vigmostad ◽  
A. Wahle ◽  
Y.-G. Lai ◽  
M. E. Olszewski ◽  
...  
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Fluid Dynamic ◽  
Critical Role ◽  
Three Dimensional ◽  
Cardiac Contraction ◽  
Local Geometry ◽  
Arbitrary Lagrangian Eulerian ◽  
Computational Fluid Dynamic Analysis ◽  
Before And After

Coronary artery disease (CAD) is characterized by the progression of atherosclerosis, a complex pathological process involving the initiation, deposition, development, and breakdown of the plaque. The blood flow mechanics in arteries play a critical role in the targeted locations and progression of atherosclerotic plaque. In coronary arteries with motion during the cardiac contraction and relaxation, the hemodynamic flow field is substantially different from the other arterial sites with predilection of atherosclerosis. In this study, our efforts focused on the effects of arterial motion and local geometry on the hemodynamics of a left anterior descending (LAD) coronary artery before and after clinical intervention to treat the disease. Three-dimensional (3D) arterial segments were reconstructed at 10 phases of the cardiac cycle for both pre- and postintervention based on the fusion of intravascular ultrasound (IVUS) and biplane angiographic images. An arbitrary Lagrangian-Eulerian formulation was used for the computational fluid dynamic analysis. The measured arterial translation was observed to be larger during systole after intervention and more out-of-plane motion was observed before intervention, indicating substantial alterations in the cardiac contraction after angioplasty. The time averaged axial wall shear stress ranged from −0.2to9.5Pa before intervention compared to −0.02to3.53Pa after intervention. Substantial oscillatory shear stress was present in the preintervention flow dynamics compared to that in the postintervention case.

CFD SIMULATION OF SHEAR STRESS AND SECONDARY FLOWS IN URETHRA

2007 ◽  
Vol 19 (02) ◽  
pp. 117-127 ◽  
Author(s):  
Yang-Yao Niu ◽  
Ding-Yu Chang
Keyword(s):  
Shear Stress ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Normal Female ◽  
Urinary System ◽  
Stress Distributions ◽  
Computational Fluid Dynamics Cfd ◽  
Peak Value ◽  
Lower Urinary

In this work, a preliminary numerical simulation of the lower urinary system using Computational Fluid Dynamics (CFD) is performed. Very few studies have been done on the simulation of three-dimensional urine through the lower urinary system. In this study, a simplified lower urinary model with rigid body assumption is proposed. The distributions of urine flow velocity, wall pressure and shear stress along the urethra are simulated based on MRI scanned uroflowmetry of a normal female. Numerical results show that violent secondary flows appear on the cross surface near the end of the urethra when the inflow rate is increased. The oscillative variation of pressure and shear stress distributions are found around the beginning section of the urethra when flow rate is at the peak value.

CFD Prediction of the Effects of Surface Roughness on Elastohydrodynamic Lubrication under Rolling/Sliding Conditions

2012 ◽  
Vol 184-185 ◽  
pp. 86-89 ◽  
Author(s):  
Shian Gao ◽  
Sutthinan Srirattayawong
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Hertzian Contact ◽  
Pure Rolling ◽  
Large Fluctuations ◽  
Two Parameters

The surface roughness plays an important role in elastohydrodynamic lubrication (EHL). To improve the lubrication system the flow behavior and lubrication mechanism must be understood, especially in the thin film classification. The effects of surface roughness in the EHL problem are complicated and difficult to measure by experiment. Therefore numerical simulation using the computational fluid dynamic (CFD) approach is proposed in this research. The CFD model developed has taken the arbitrary surface roughness into consideration, and has been used to predict the characteristics of fluid flow, such as the pressure distribution, the minimal film thickness and the shear stress. The cylinder is considered to be under elastic deformation according to the theory of Hertzian contact and the surface of cylinder is defined to have an arbitrary roughness. The simulation results show that the surface roughness has significant effects on the pressure profile and shear stress, especially in the case of pure rolling, where the two parameters in the rough surface case show large fluctuations that are much higher than the corresponding smooth surface case.

Unsteady Responses of the Impeller of a Centrifugal Compressor Exposed to Pulsating Backpressure

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Mengying Shu ◽  
Mingyang Yang ◽  
Ricardo F. Martinez-Botas ◽  
Kangyao Deng ◽  
Lei Shi
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Combustion Engine ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Intake Manifold ◽  
Unsteady Simulation

The flow in intake manifold of a heavily downsized internal combustion engine has increased levels of unsteadiness due to the reduction of cylinder number and manifold arrangement. The turbocharger compressor is thus exposed to significant pulsating backpressure. This paper studies the response of a centrifugal compressor to this unsteadiness using an experimentally validated numerical method. A computational fluid dynamic (CFD) model with the volute and impeller is established and validated by experimental measurements. Following this, an unsteady three-dimensional (3D) simulation is conducted on a single passage imposed by the pulsating backpressure conditions, which are obtained by one-dimensional (1D) unsteady simulation. The performance of the rotor passage deviates from the steady performance and a hysteresis loop, which encapsulates the steady condition, is formed. Moreover, the unsteadiness of the impeller performance is enhanced as the mass flow rate reduces. The pulsating performance and flow structures near stall are more favorable than those seen at constant backpressure. The flow behavior at points with the same instantaneous mass flow rate is substantially different at different time locations on the pulse. The flow in the impeller is determined by not only the instantaneous boundary condition but also by the evolution history of flow field. This study provides insights in the influence of pulsating backpressure on compressor performance in actual engine situations, from which better turbo-engine matching might be benefited.

Patient-specific three-dimensional simulation of LDL accumulation in a human left coronary artery in its healthy and atherosclerotic states

2009 ◽  
Vol 296 (6) ◽  
pp. H1969-H1982 ◽  
Author(s):  
Ufuk Olgac ◽  
Dimos Poulikakos ◽  
Stefan C. Saur ◽  
Hatem Alkadhi ◽  
Vartan Kurtcuoglu
Keyword(s):  
Shear Stress ◽  
Coronary Artery ◽  
Left Coronary Artery ◽  
Three Dimensional ◽  
Arterial Blood Flow ◽  
Patient Specific ◽  
Computed Tomography Images ◽  
Arterial Blood ◽  
Diseased State ◽  
Stress Dependent

We calculate low-density lipoprotein (LDL) transport from blood into arterial walls in a three-dimensional, patient-specific model of a human left coronary artery. The in vivo anatomy data are obtained from computed tomography images of a patient with coronary artery disease. Models of the artery anatomy in its healthy and diseased states are derived after segmentation of the vessel lumen, with and without the detected plaque, respectively. Spatial shear stress distribution at the endothelium is determined through the reconstruction of the arterial blood flow field using computational fluid dynamics. The arterial endothelium is represented by a shear stress-dependent, three-pore model, taking into account blood plasma and LDL passage through normal junctions, leaky junctions, and the vesicular pathway. Intraluminal pressures of 70 and 120 mmHg are employed as the normal and hypertensive operating pressures, respectively. By applying our model to both the healthy and diseased states, we show that the location of the plaque in the diseased state corresponds to one of the two sites with predicted high-LDL concentration in the healthy state. We further show that, in the diseased state, the site with high-LDL concentration has shifted distal to the plaque, which is in agreement with the clinical observation that plaques generally grow in the downstream direction. We also demonstrate that hypertension leads to increased number of regions with high-LDL concentration, elucidating one of the ways in which hypertension may promote atherosclerosis.

Development of a Three-Dimensional Iterative Methodology Using a Commercial CFD Code for Flow Scouring Around Bridge Piers

2012 ◽  
Author(s):  
Phani Ganesh Elapolu ◽  
Pradip Majumdar ◽  
Steven A. Lottes ◽  
Milivoje Kostic
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Shear Stresses ◽  
Computational Domain ◽  
Time Step ◽  
Mesh Morphing ◽  
River Bed ◽  
Scour Hole ◽  
The Stability

One of the major concerns affecting the safety of bridges with foundation supports in river-beds is the scouring of river-bed material from bridge supports during floods. Scour is the engineering term for the erosion caused by water around bridge elements such as piers, monopiles, or abutments. Scour holes around a monopile can jeopardize the stability of the whole structure and will require deeper piling or local armoring of the river-bed. About 500,000 bridges in the National Bridge Registry are over waterways. Many of these are considered as vulnerable to scour, about five percent are classified as scour critical, and over the last 30 years bridge failures caused by foundation scour have averaged about one every two weeks. Therefore it is of great importance to predict the correct scour development for a given bridge and flood conditions. Apart from saving time and money, integrity of bridges are important in ensuring public safety. Recent advances in computing boundary motion in combination with mesh morphing to maintain mesh quality in computational fluid dynamic analysis can be applied to predict the scour hole development, analyze the local scour phenomenon, and predict the scour hole shape and size around a pier. The main objective of the present study was to develop and implement a three dimensional iterative procedure to predict the scour hole formation around a cylindrical pier using the mesh morphing capabilities in the STARCCM+ commercial CFD code. A computational methodology has been developed using Python and Java Macros and implemented using a Bash script on a LINUX high performance computer cluster. An implicit unsteady approach was used to obtain the bed shear stresses. The mesh was iteratively deformed towards the equilibrium scour position based on the excess shear stress above the critical shear stress (supercritical shear stress). The model solves the flow field using Reynolds Averaged Navier-Stokes (RANS) equations, and the standard k–ε turbulence model. The iterative process involves stretching (morphing) a meshed domain after every time step, away from the bottom where scouring flow parameters are supercritical, and remeshing the relevant computational domain after a certain number of time steps when the morphed mesh compromises the stability of further simulation. The simulation model was validated by comparing results with limited experimental data available in the literature.

scholarly journals Numerical Simulation of Dispersed Particle-Blood Flow in the Stenosed Coronary Arteries

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Mongkol Kaewbumrung ◽  
Somsak Orankitjaroen ◽  
Pichit Boonkrong ◽  
Buraskorn Nuntadilok ◽  
Benchawan Wiwatanapataphee
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Shear Stress ◽  
Coronary Artery ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Stokes Equations ◽  
Spherical Shape ◽  
Shear Stresses ◽  
Wall Shear

A mathematical model of dispersed bioparticle-blood flow through the stenosed coronary artery under the pulsatile boundary conditions is proposed. Blood is assumed to be an incompressible non-Newtonian fluid and its flow is considered as turbulence described by the Reynolds-averaged Navier-Stokes equations. Bioparticles are assumed to be spherical shape with the same density as blood, and their translation and rotational motions are governed by Newtonian equations. Impact of particle movement on the blood velocity, the pressure distribution, and the wall shear stress distribution in three different severity degrees of stenosis including 25%, 50%, and 75% are investigated through the numerical simulation using ANSYS 18.2. Increasing degree of stenosis severity results in higher values of the pressure drop and wall shear stresses. The higher level of bioparticle motion directly varies with the pressure drop and wall shear stress. The area of coronary artery with higher density of bioparticles also presents the higher wall shear stress.

Flow Characteristics Inside Circular Injection Holes Normally Oriented to a Crossflow: Part II—Three-Dimensional Flow Data and Aerodynamic Loss

2000 ◽  
Vol 123 (2) ◽  
pp. 274-280 ◽  
Author(s):  
Sang Woo Lee ◽  
Seong Kuk Joo ◽  
Joon Sik Lee
Keyword(s):  
Secondary Flow ◽  
Separation Bubble ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Windward Side ◽  
Leeward Side ◽  
Injection Hole ◽  
Potential Core ◽  
Aerodynamic Loss

Presented are three-dimensional mean velocity components and aerodynamic loss data inside circular injection holes. The holes are normally oriented to a crossflow and each hole has a sharp square-edged inlet. Because of their importance to flow behavior, three different blowing ratios, M=0.5, 1.0, and 2.0, and three hole length-to-diameter ratios, L/D=0.5, 1.0, and 2.0, are investigated. The entry flow is characterized by a separation bubble, and the exit flow is characterized by direct interaction with the crossflow. The uniform oncoming flow at the inlet undergoes a strong acceleration and a subsequent gradual deceleration along a converging–diverging flow passage formed by the inlet separation bubble. After passing the throat of the converging–diverging passage, the potential core flow, which is nearly axisymmetric, decelerates on the windward side, but tends to accelerate on the leeward side. The presence of the crossflow thus reduces the discharge of the injectant on the windward side, but enhances its efflux on the leeward side. This trend is greatly accentuated at M=0.5. In general, there are strong secondary flows in the inlet and exit planes of the injection hole. The secondary flow within the injection hole, on the other hand, is found to be relatively weak. The inlet secondary flow is characterized by a strong inward flow toward the injection-hole center. However, it is not completely directed inward since the crossflow effect is superimposed on it. Past the throat, secondary flow is observed such that the leeward velocity component induced by the crossflow is superimposed on the diverging flow. Short L/D usually results in an exit discharging flow with a steep velocity gradient as well as a strong deceleration on the windward side, as does low M. The aerodynamic loss inside the injection hole originates from the inlet separation bubble, wall friction and interaction of the injectant with the crossflow. The first one is considered as the most dominant source of loss, even in the case of L/D=2.0. At L/D=0.5, the first and third sources are strongly coupled with each other. Regardless of L/D, the mass-averaged aerodynamic loss coefficient has an increasing tendency with increasing M.

Mass Transport and Shear Stress in a Microchannel Bioreactor: Numerical Simulation and Dynamic Similarity

2005 ◽  
Vol 128 (2) ◽  
pp. 185-193 ◽  
Author(s):  
Yan Zeng ◽  
Thong-See Lee ◽  
Peng Yu ◽  
Partha Roy ◽  
Hong-Tong Low
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Mass Transport ◽  
Flow Model ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Dynamic Similarity ◽  
Simplified Analysis ◽  
Combined Parameters ◽  
Substrate Concentrations

Microchannel bioreactors have been used in many studies to manipulate and investigate the fluid microenvironment around cells. In this study, substrate concentrations and shear stresses at the base were computed from a three-dimensional numerical flow-model incorporating mass transport. Combined dimensionless parameters were developed from a simplified analysis. The numerical results of substrate concentration were well correlated by the combined parameters. The generalized results may find applications in design analysis of microchannel bioreactors. The mass transport and shear stress were related in a generalized result. Based on the generalized results and the condition of dynamic similarity, various means to isolate their respective effects on cells were considered.

Three-Dimensional Numerical Simulation of the Fluid Dynamics in a Coronary Stent

2009 ◽  
Author(s):  
F. Gori ◽  
A. Boghi ◽  
M. Amitrano
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Coronary Stent ◽  
Shear Stresses ◽  
Unsteady State ◽  
Hemodynamic Variables ◽  
Stent Geometry ◽  
Severe Coronary Artery ◽  
Wall Shear ◽  
Artery Disease

Stents are commonly used to restore blood flow in patients with severe coronary artery disease. Local hemodynamic variables, as wall shear stress, have an important role in the restenosis and their distribution depends on the stent geometry. The objective of the present study is to carry out CFD simulations in a realistic 3D geometry of a coronary stent in physiological conditions. A comparison is performed between two reconstructed stents, made of 12 rings and similar to the real coronary ones, which differ by the position of the struts, where the first type is with closed cells and the second one with open cells. The artery is modeled as a cylinder with rigid walls and the blood is assumed as incompressible Newtonian fluid in laminar flow with constant physical properties. The commercial computational fluid dynamic code FLUENT is used with a mesh composed of non uniform tetrahedrons. The simulations are performed in steady and unsteady state. Wall shear stresses, WSS, as well as its time variations, are investigated in unsteady state with the conclusion that the stent with closed cells have a better fluid dynamic behavior.

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