Three-Dimensional Numerical Simulations of Peristaltic Contractions in Obstructed Ureter Flows

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Zahra Najafi ◽  
Prashanta Gautam ◽  
Bradley F. Schwartz ◽  
Abhilash J. Chandy ◽  
Ajay M. Mahajan
Keyword(s):  
Three Dimensional ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Ansys Fluent ◽  
Commercial Code ◽  
Peristaltic Movement ◽  
Mass Flow Rates ◽  
Wall Shear ◽  
Ureteral Peristalsis ◽  
Peristaltic Contractions

Ureteral peristalsis can be considered as a series of waves on the ureteral wall, which transfers the urine along the ureter toward the bladder. The stones that form in the kidney and migrate to the ureter can create a substantial health problem due to the pain caused by interaction of the ureteral walls and stones during the peristaltic motion. Three-dimensional (3D) computational fluid dynamics (CFD) simulations were carried out using the commercial code ansys fluent to solve for the peristaltic movement of the ureter, with and without stones. The effect of stone size was considered through the investigation of varying obstructions of 5%, 15%, and 35% for fixed spherical stone shape. Also, an understanding of the effect of stone shape was obtained through separate CFD calculations of the peristaltic ureter with three different types of stones, a sphere, a cube, and a star, all at a fixed obstruction percentage of 15%. Velocity vectors, mass flow rates, pressure gradients, and wall shear stresses were analyzed along one bolus of urine during peristalsis of the ureteral wall to study the various effects. It was found that the increase in obstruction increased the backflow, pressure gradients, and wall shear stresses proximal to the stone. On the other hand, with regard to the stone shape study, while the cube-shaped stones resulted in the largest backflow, the star-shaped stone showed highest pressure gradient magnitudes. Interestingly, the change in stone shape did not have a significant effect on the wall shear stress at the obstruction level studied here.

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.

scholarly journals A Novel Catalytic Micro-Combustor Inspired by the Nasal Geometry of Reindeer: CFD Modeling and Simulation

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 606
Author(s):  
Valeria Di Sarli ◽  
Marco Trofa ◽  
Almerinda Di Benedetto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Residence Time ◽  
Convective Heat Transfer Coefficient ◽  
Three Dimensional ◽  
Cfd Modeling ◽  
Ansys Fluent ◽  
Commercial Code ◽  
Micro Combustor

A three-dimensional CFD model of a novel configuration of catalytic micro-combustor inspired by the nasal geometry of reindeer was developed using the commercial code ANSYS Fluent 19.0. The thermal behavior of this nature-inspired (NI) configuration was investigated through simulations of lean propane/air combustion performed at different values of residence time (i.e., inlet gas velocity) and (external convective) heat transfer coefficient. Simulations at the same conditions were also run for a standard parallel-channel (PC) configuration of equivalent dimensions. Numerical results show that the operating window of stable combustion is wider in the case of the NI configuration. In particular, the blow-out behavior is substantially the same for the two configurations. Conversely, the extinction behavior, which is dominated by competition between the heat losses towards the external environment and the heat produced by combustion, differs. The NI configuration exhibits a greater ability than the PC configuration to keep the heat generated by combustion trapped inside the micro-reactor. As a consequence, extinction occurs at higher values of residence time and heat transfer coefficient for this novel configuration.

Gerotor Fuel Pump Performance and Leakage Study

2011 ◽  
Author(s):  
Mario Alberto Ruvalcaba ◽  
Xiao Hu
Keyword(s):  
Three Dimensional ◽  
Tip Clearance ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Pump Performance ◽  
Pump Flow ◽  
Automotive Fuel ◽  
Commercial Code ◽  
Gerotor Pumps ◽  
Good Agreement

Gerotor pumps are utilized in a number of automotive applications such as fuel lift. Volumetric efficiency and leakage are causes of concern in gerotor pumps. To optimize pump performance and reduce leakage, it is fundamental to comprehend the fluid dynamics inside the pump passageways. In this paper, a three-dimensional CFD methodology has been developed and applied to predict the pump performance, to understand pump flow dynamics and to investigate pump leakage for gerotor pumps equipped in automotive fuel systems. The methodology is based in the commercial code ANSYS FLUENT and the analytical focal points are the pump performance and leakage over a range of motor speeds and output pressures, 4000 RPM and 5400 RPM, also 450 kPa and 600 kPa. The CFD results are first contrasted with the experimental data and a very good agreement has been achieved. Extensive CFD simulations are then conducted to study the effect of the tip clearance on pump flow performance and leakage.

Unsteady and Three-Dimensional Simulation of Blood Flow in the Human Aortic Arch

2002 ◽  
Vol 124 (4) ◽  
pp. 378-387 ◽  
Author(s):  
N. Shahcheraghi ◽  
H. A. Dwyer ◽  
A. Y. Cheer ◽  
A. I. Barakat ◽  
T. Rutaganira
Keyword(s):  
Blood Flow ◽  
Aortic Arch ◽  
Thoracic Aorta ◽  
Aortic Wall ◽  
Three Dimensional ◽  
Outer Wall ◽  
Human Aorta ◽  
Shear Stresses ◽  
Descending Thoracic Aorta ◽  
Wall Shear

A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.

scholarly journals Efficient investigation on fully developed flow in a mildly curved 180° open-channel

2014 ◽  
Vol 16 (6) ◽  
pp. 1250-1264 ◽  
Author(s):  
Yuchuan Bai ◽  
Xiaolong Song ◽  
Shuxian Gao
Keyword(s):  
Secondary Flow ◽  
Flow Pattern ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Engineering Application ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Fully Developed Flow ◽  
Wall Shear ◽  
Volume Method

Turbulent flow in meandering open channels is one of the most complicated and unpredictable turbulent flows as the interaction of various forces, such as pressure gradient, centrifugal force, and wall shear stresses severely affect the flow pattern. In order to improve significance in engineering application, understanding the overall flow characteristic is the focus. This paper presents the results of numerical and experimental investigations of flow in a 180° mild bend, which is close to criticality with curvature ratio R/B = 3. Considering the characteristic of various models, three-dimensional (3D) re-normalization group (RNG) k–ε model was adopted to simulate the flow efficiently. Governing equations of the flow were solved with a finite-volume method. The pressure-based coupled algorithm was used to compute the pressure. The flow velocities were measured experimentally with Micro acoustic Doppler velocimeter. Good agreement between the numerical results and measurements indicated that RNG k–ε model can successfully predict this flow phenomenon. The flow pattern in this bend is influenced widely by the secondary flow. The variations of velocity components, streamlines, secondary flow, and wall shear stresses are analysed in the study. Some newly discovered phenomenon in this special state are worth noting.

scholarly journals NUMERICAL EVALUATION OF CURVATURE EFFECTS ON SHEAR STRESSES ACROSS ARTERIAL STENOSES

2002 ◽  
Vol 14 (04) ◽  
pp. 164-170 ◽  
Author(s):  
YANG-YAO NIU ◽  
WEI-KUANG CHU ◽  
LUNG-CHENG LEE ◽  
HSI-YU YU
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Arterial Walls ◽  
Curvature Effects ◽  
Newtonian Flows ◽  
Flow Features ◽  
Wall Shear ◽  
Arterial Stenoses

In this study, Newtonian flows passing through three-dimensional curved and straight axissymmetrical stenotic tubes are investigated. The geometry effects and Reynolds numbers of 100, 200, 400, and 600 on the formation of the shear rate over arterial walls are studied. It is noted that geometric effects on flow features such as velocity profiles, pressure and wall shear stress distributions in the post-stenotic region are significant. The location of maximum wall shear stress is found to relate to the geometric effect much than the Reynolds number effect.

scholarly journals Computational Analysis of Wall Shear Stress Patterns on Calcified and Bicuspid Aortic Valves: Focus on Radial and Coaptation Patterns

Fluids ◽  
2021 ◽  
Vol 6 (8) ◽  
pp. 287
Author(s):  
Huseyin Enes Salman ◽  
Levent Saltik ◽  
Huseyin C. Yalcin
Keyword(s):  
Aortic Valve ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Aortic Valves ◽  
Bicuspid Valve ◽  
Valve Function ◽  
Valvular Diseases ◽  
Wall Shear ◽  
Stress Patterns ◽  
Valve Formation

Calcification and bicuspid valve formation are important aortic valve disorders that disturb the hemodynamics and the valve function. The detailed analysis of aortic valve hemodynamics would lead to a better understanding of the disease’s etiology. We computationally modeled the aortic valve using simplified three-dimensional geometry and inlet velocity conditions obtained via echocardiography. We examined various calcification severities and bicuspid valve formation. Fluid-structure interaction (FSI) analyses were adapted using ANSYS Workbench to incorporate both flow dynamics and leaflet deformation accurately. Simulation results were validated by comparing leaflet movements in B-mode echo recordings. Results indicate that the biomechanical environment is significantly changed for calcified and bicuspid valves. High flow jet velocities are observed in the calcified valves which results in high transvalvular pressure difference (TPG). Wall shear stresses (WSS) increased with the calcification on both fibrosa (aorta side) and ventricularis (left ventricle side) surfaces of the leaflet. The WSS distribution is regular on the ventricularis, as the WSS values proportionally increase from the base to the tip of the leaflet. However, WSS patterns are spatially complex on the fibrosa side. Low WSS levels and spatially complex WSS patterns on the fibrosa side are considered as promoting factors for further calcification and valvular diseases.

3D CFD Simulation of Water Hammer Through a 90° Bend: Applicability of URANS, 3D Effects and Unsteady Friction

2014 ◽  
Author(s):  
Stefan Riedelmeier ◽  
Stefan Becker ◽  
Eberhard Schlücker
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Water Hammer ◽  
Dynamics Simulation ◽  
Shear Stresses ◽  
Velocity Gradients ◽  
Wall Shear ◽  
The Impact

In most cases, the method of characteristics is used to calculate the propagation of water hammer in hydraulic systems due to the size of those pipings, although three-dimensional effects are known to occur. In order to investigate and quantify these effects, a three-dimensional computational fluid dynamics simulation of water hammer through a bend geometry was performed. For the resolution of the developing high spatial and temporal gradients an adequate mesh and suitable physical model was generated using a commercial code. The applicability of unsteady Reynolds-averaged Navier-Stokes simulation was evaluated considering the turbulent properties of the flow using results from the literature. Furthermore velocity, pressure, wall shear stress and vorticity distributions are presented. The effect of the 90° bend as three-dimensional element was identified and the impact on the flow field is presented. In the end, the annular effect is discussed. Due to the high forces of inertia in the boundary layer and the dominating viscous forces close to the wall, high velocity gradients are developing resulting in high wall shear stresses. It is shown that the viscous and turbulent transport of momentum in the radial direction reduces these velocity gradients and limits the maximum occurring wall shear stress.

Hydrodynamic Effects of Compliance Mismatch in Stented Arteries

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
N. K. C. Selvarasu ◽  
Danesh K. Tafti ◽  
Pavlos P. Vlachos
Keyword(s):  
Elastic Modulus ◽  
Coronary Artery ◽  
Pressure Gradient ◽  
Treatment Options ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Local Pressure ◽  
Wall Shear ◽  
Vorticity Flux ◽  
Compliance Mismatch

Cardiovascular diseases are the number one cause of death in the world, making the understanding of hemodynamics and development of treatment options imperative. The most common modality for treatment of occlusive coronary artery diseases is the use of stents. Stent design profoundly influences the postprocedural hemodynamic and solid mechanical environment of the stented artery. However, despite their wide acceptance, the incidence of stent late restenosis is still high (Zwart et al., 2010, “Coronary Stent Thrombosis in the Current Era: Challenges and Opportunities for Treatment,” Current Treatment Options in Cardiovascular Medicine, 12(1), pp. 46–57), and it is most prevailing at the proximal and distal ends of the stent. In this work, we focus our investigation on the localized hemodynamic effects of compliance mismatch due to the presence of a stent in an artery. The compliance mismatch in a stented artery is maximized at the proximal and distal ends of the stent. Hence, it is our objective to understand and reveal the mechanism by which changes in compliance contribute to the generation of nonphysiological wall shear stress (WSS). Such adverse hemodynamic conditions could have an effect on the onset of restenosis. Three-dimensional, spatiotemporally resolved computational fluid dynamics simulations of pulsatile flow with fluid-structure interaction were carried out for a simplified coronary artery with physiologically relevant flow parameters. A model with uniform elastic modulus is used as the baseline control case. In order to study the effect of compliance variation on local hemodynamics, this baseline model is compared with models where the elastic modulus was increased by two-, five-, and tenfold in the middle of the vessel. The simulations provided detailed information regarding the recirculation zone dynamics formed during flow reversals. The results suggest that discontinuities in compliance cause critical changes in local hemodynamics, namely, altering the local pressure and velocity gradients. The change in pressure gradient at the discontinuity was as high as 90%. The corresponding changes in WSS and oscillatory shear index calculated were 9% and 15%, respectively. We demonstrate that these changes are attributed to the physical mechanism associating the pressure gradient discontinuities to the production of vorticity (vorticity flux) due to the presence of the stent. The pressure gradient discontinuities and augmented vorticity flux are affecting the wall shear stresses. As a result, this work reveals how compliance variations act to modify the near wall hemodynamics of stented arteries.

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