PULSATILE FLOW FIELDS IN A MODEL OF ABDOMINAL AORTA WITH ITS PERIPHERAL BRANCHES

2003 ◽  
Vol 15 (05) ◽  
pp. 170-178 ◽  
Author(s):  
D. LEE ◽  
J. Y. CHEN
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Abdominal Aorta ◽  
Pulsatile Flow ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Computer Code ◽  
Flow Fields ◽  
Dynamic Factors ◽  
Recirculation Zones

In a previous study by the authors, steady flow fields in a model of abdominal aorta with its seven peripheral branches were reported. In the present study, the some aorta model was simulated numerically with a pulsatile inlet waves for both the resting and exercise conditions. The baseline pulsatile flow field was presented in terms of velocity vectors and iso-velocity contours as well as the wall shear stress (WSS) distribution and the recirculation zones. The time-averaged behavior of the flow field represented by the fluid dynamic factors was discussed. The results were consistent with those obtained experimentally and numerically by other investigators. It was also found that under the present conditions, the steady flow behavior could adequately describe the time-averaged behavior of its corresponding pulsatile case, particularly in the regions where convective flow dominated. The present computer code may provide a platform for clinical simulations.

scholarly journals Numerical and Analytical Study of Fluid Dynamic Forces in Seals and Bearings

1988 ◽  
Vol 110 (3) ◽  
pp. 315-325 ◽  
Author(s):  
L. T. Tam ◽  
A. J. Przekwas ◽  
A. Muszynska ◽  
R. C. Hendricks ◽  
M. J. Braun ◽  
...  
Keyword(s):  
Flow Field ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Circumferential Velocity ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Lumped Model ◽  
Destabilizing Factors ◽  
Recirculation Zones

A numerical model based on a transformed, conservative form of the three-dimensional Navier-Stokes equations and an analytical model based on “lumped” fluid parameters are presented and compared with studies of modeled rotor/bearing/seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a descrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three-dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity, while injection or preswirl in the direction of rotation significantly weakened these zones. A decrease in average circumferential velocity was related to an increase in the strength of the recirculation zones and thereby promoted stability. The influence of the axial flow was analyzed. The lumped model of fluid dynamic force based on the average circumferential velocity ratio (as opposed to the bearing/seal coefficient model) well described the obtained results for relatively large but limited ranges of parameters. This lumped model is extremely useful in rotor/bearing/seal system dynamic analysis and should be widely recommended. Fluid dynamic forces and leakage rates were calculated and compared with seal data where the working fluid was bromotrifluoromethane (CBrF3). The radial and tangential force predictions were in reasonable agreement with selected experimental data. Nonsynchronous perturbation provided meaningful information for system lumped parameter identification from numerical experiment data.

DIAGNOSTIC AND THERAPEUTIC TREATMENTS OF PLAQUES IN THE CAROTID BIFURCATION — STUDIES IN MODELS WITH STENTS AND FILTERS

2014 ◽  
Vol 14 (03) ◽  
pp. 1450030
Author(s):  
D. LIEPSCH ◽  
A. BALASSO ◽  
C. ZIMMER ◽  
H. BERGER ◽  
R. BURKHART ◽  
...  
Keyword(s):  
Flow Rate ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Carotid Bifurcation ◽  
Flow Rate Ratio ◽  
Shear Stresses ◽  
Dynamic Factors ◽  
Rate Ratios ◽  
Visualization Techniques

Fluid dynamics, especially forces and velocity distribution, influence the development of plaques. Flow parameters: pulsatility, the non-Newtonian flow behavior of blood and wall elasticity are considered. Flow visualization techniques (dyes and birefringent solution with a photo-elasticity apparatus) and LDA measurements demonstrate the importance of the flow. Accurate in vivo velocity measurements are necessary to calculate shear stresses. Different bifurcation angles and flow rate ratios were tested in true to life artery models. The most important fluid dynamic factors at bifurcations are the flow rate ratio and the geometry which create flow separation regions which are responsible for platelet aggregation and intima damage. It is necessary to measure all three velocity components to calculate the velocity vector. The highest shear stresses in a healthy carotid artery are 16 Pa and are found just at the apex. In artery models with 90% stenosis, shear stresses up to 250 Pa were found. Distally, vortices were created where particles remained over several pulse cycles. Measurements show that stents must be selected carefully and placed precisely. Filters must be closed during the systolic phase before removal, so that no trapped particles can escape.

Flow Visualization Studies in a Mold of the Normal Human Aorta and Renal Arteries

1989 ◽  
Vol 111 (3) ◽  
pp. 222-227 ◽  
Author(s):  
D. Liepsch ◽  
A. Poll ◽  
J. Strigberger ◽  
H. N. Sabbah ◽  
P. D. Stein
Keyword(s):  
Steady Flow ◽  
Flow Separation ◽  
Pulsatile Flow ◽  
Flow Behavior ◽  
Renal Arteries ◽  
Human Aorta ◽  
Flow Disturbances ◽  
Disturbed Areas ◽  
Entire Flow ◽  
Normal Human

To study the flow behavior in regions where hemodynamic effects have been suggested to participate in atherogenesis, we evaluated flow in a mold of the aorta and renal arteries of a previously healthy 27-year-old woman who died of trauma. A birefringent solution (vanadium-pentoxide) was used. When diluted, this material behaves like a Newtonian fluid. This method gives a complete picture of the entire flow field. Zones of flow separation and disturbed flow can be seen and the location and size of disturbed areas observed. Unseparated flow regions downstream from disturbed zones can be properly visualized and the method can be used for pulsatile flow as well as steady flow. During steady flow (only at branch to-trunk flow ratios > 0.20), zones of flow separation were observed in the aorta distal to the renal arteries. During pulsatile flow, disturbances were found at nearly all branch-to-trunk flow ratios.

LDA Study of the Flow Associated With the Design Differences and Orientations of the Bileaflet Mechanical Prostheses

2000 ◽  
Author(s):  
Toshinosuke Akutsu ◽  
Daiki Higucchi ◽  
Tomohiro Taguchi
Keyword(s):  
Flow Field ◽  
Pulsatile Flow ◽  
Heart Valves ◽  
Flow Fields ◽  
Flow Conditions ◽  
Jude Medical ◽  
Mitral Position ◽  
Highly Sensitive ◽  
Mechanical Prostheses ◽  
Two Component

Abstract Four typical mechanical bileaflet heart valves (St. Jude Medical, Advancing The Standard, Carbomedics, and Jyros valves) have been tested in the mitral position under pulsatile flow conditions. Measurements of velocity and turbulent stresses were conducted at five downstream locations using a sophisticated cardiac simulator in conjunction with a highly sensitive two-component LDA. Comparison of these flow fields associated with the opening and subsequent accelerating phase of the flow revealed similarity and dissimilarity of the flow field associated with the different valve designs and helped established visualizing the effect of the valve designs and orientations on the flow.

Analysis of Volumetric Residence Time of Blood Elements in Stenosed Arteries

2003 ◽  
Author(s):  
M. C. Kim ◽  
C. S. Lee ◽  
C. J. Kim
Keyword(s):  
Residence Time ◽  
Transient Flow ◽  
Fluid Dynamic ◽  
Viscous Drag ◽  
Shear Stresses ◽  
Drag Forces ◽  
Area Reduction ◽  
Dynamic Factors ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd

Blood flow in arteries is known to be closely related to atherosclerosis. Presence of recirculation zones, and low, high, and oscillatory wall shear stresses have been suggested to be important fluid dynamic factors causing development and progress of atherosclerosis. Our study was motivated to develop fluid mechanical indices between residence time of blood particles in arteries and atherosclerosis. In rigid models of stenosed arteries with 75% area reduction, trajectories of blood particles were numerically computed and used to determine local volumetric residence time (VRT) of platelets. The motion of particles in the model artery was computed by considering viscous drag forces between blood particles and presolved transient flow field from computational fluid dynamics (CFD). Many cardiac cycles were considered in the computation to reflect temporally accumulative characteristics of VRT in the recirculation zones. Our results showed that VRT in the recirculation zone was relatively low in the first cardiac cycle. However it increased in the subsequent cycles as more particles were trapped in the same zone. The results suggested that VRT contour calculated in the present study would be an effective indicator of the presence of atherosclerosis.

Investigation of the Flow Field in a HP Turbine Stage for Two Stator-Rotor Axial Gaps: Part I — 3D Time-Averaged Flow Field

2006 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Flow Fields ◽  
Secondary Flows ◽  
Point Of View ◽  
Flow Structures ◽  
Axial Distance ◽  
Turbine Stage ◽  
Subsonic Regime ◽  
Definition Of

An extensive experimental analysis on the subject of unsteady flow field in high pressure turbine stages was carried out at the Laboratorio di Fluidodinamica delle Macchine (LFM) of Politecnico di Milano. The research stage represents a typical modern HP gas turbine stage designed by means of 3D techniques, characterised by a leaned stator and a bowed rotor and operating in high subsonic regime. The first part of the program concerns the analysis of the steady flow field in the stator-rotor axial gap by means of a conventional five-hole probe and a temperature sensor. Measurements were carried out on eight planes located at different axial positions allowing the complete definition of steady flow field both in absolute and relative frame of reference. The evolution of the main flow structures, such as secondary flows and vane wakes, downstream of the stator are here presented and discussed in order to evidence the stator aerodynamic performance and, in particular, the different flow field approaching the rotor blade row for the two axial gaps. This results set will support the discussion of the unsteady stator-rotor effects presented in paper Part II. Furthermore, 3D time-averaged measurements downstream of the rotor were carried out at one axial distance and for two stator-rotor axial gaps. The position of the probe with respect to the stator blades is changed by means of rotating the stator in circumferential direction, in order to describe possible effects of the non-uniformity of the stator exit flow field downstream of the stage. Both flow fields, measured for the nominal and for a very large stator-rotor axial gap, are discussed and results show the persistence of some stator flow structures downstream of the rotor, in particular for the minimum axial gap. Eventually the flow fields are compared to evidence the effect of the stator-rotor axial gap on the stage performance from a time-averaged point of view.

Influence of Guide Vanes' Angle on Flow Fields of Cylinder Cage Powder Classifier

2012 ◽  
Vol 263-266 ◽  
pp. 843-846 ◽  
Author(s):  
Da Zhi Jiang ◽  
Jing Han
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Flow Behavior ◽  
Air Flow ◽  
Flow Fields ◽  
Guide Vanes ◽  
Flow Field Characteristics ◽  
Computational Fluid Dynamics Cfd ◽  
The Stability

To research guide vanes' influences on flow fields of cylinder cage powder classifier at different angles, a study of guide vanes under 3 different angles is therefore undertaken examining air flow behavior. The investigation of these flow field characteristics made use of the computational fluid dynamics (CFD) to simulate the air flow in the classifier. The results indicate that smaller angles of guide vanes can increase velocity but damage the stability of flow fields, and that those larger angles will reduce the velocity.

Evaluation of the Proximal Flow Field to Circular and Noncircular Orifices of Different Aspect Ratios

1997 ◽  
Vol 119 (3) ◽  
pp. 349-356 ◽  
Author(s):  
J. G. Myers ◽  
J. F. Fox ◽  
A. M. Elmahdi ◽  
G. J. Perry ◽  
A. S. Anayiotos
Keyword(s):  
Flow Field ◽  
Evaluation Method ◽  
Fluid Dynamic ◽  
Color Doppler ◽  
Flow Fields ◽  
Approximation Technique ◽  
Valvular Regurgitation ◽  
Aspect Ratios ◽  
Flow Field Characteristics

Investigations of valvular regurgitation attempt to specify flow field characteristics and apply them to the proximal isovelocity surface area (PISA) method for quantifying regurgitant flow. Most investigators assume a hemispherical shape to these equivelocity shells proximal to an axisymmetric (circular) orifice. However, in vivo flow fields are viscous and regurgitant openings vary in shape and size. By using centerline profiles and isovelocity surfaces, this investigation describes the flow field proximal to circular and elliptical orifices. Steady, proximal flow fields are obtained with two- and three-dimensional computational fluid dynamic (CFD) simulations. These simulations are verified by in vitro, laser-Doppler velocimetry (LDV) experiments. The data show that a unique, normalized proximal flow field results for each orifice shape independent of orifice flow or size. The distinct differences in flow field characteristics with orifice shape may provide a mechanism for evaluating orifice characteristics and regurgitant flows. Instead of the hemispherical approximation technique, this study attempts to show the potential to define a universal flow evaluation method based on the details of the flowfield according to orifice shape. Preliminary results indicate that Magnetic Resonance (MR) and Color Doppler (CD) may reproduce these flow details and allow such a procedure in vivo.

Direct numerical simulation of stenotic flows. Part 1. Steady flow

2007 ◽  
Vol 582 ◽  
pp. 253-280 ◽  
Author(s):  
SONU S. VARGHESE ◽  
STEVEN H. FRANKEL ◽  
PAUL F. FISCHER
Keyword(s):  
Shear Stress ◽  
Flow Field ◽  
Steady Flow ◽  
Turbulent Flows ◽  
Pulsatile Flow ◽  
Current Model ◽  
Energy Levels ◽  
Flow Analysis ◽  
Transition To Turbulence ◽  
Hairpin Vortices

Direct numerical simulations (DNS) of steady and pulsatile flow through 75% (by area reduction) stenosed tubes have been performed, with the motivation of understanding the biofluid dynamics of actual stenosed arteries. The spectral-element method, providing geometric flexibility and high-order spectral accuracy, was employed for the simulations. The steady flow results are examined here while the pulsatile flow analysis is dealt with in Part 2 of this study. At inlet Reynolds numbers of 500 and 1000, DNS predict a laminar flow field downstream of an axisymmetric stenosis and comparison to previous experiments show good agreement in the immediate post-stenotic region. The introduction of a geometric perturbation within the current model, in the form of a stenosis eccentricity that was 5% of the main vessel diameter at the throat, resulted in breaking of the symmetry of the post-stenotic flow field by causing the jet to deflect towards the side of the eccentricity and, at a high enough Reynolds number of 1000, jet breakdown occurred in the downstream region. The flow transitioned to turbulence about five diameters away from the stenosis, with velocity spectra taking on a broadband nature, acquiring a -5/3 slope that is typical of turbulent flows. Transition was accomplished by the breaking up of streamwise, hairpin vortices into a localized turbulent spot, reminiscent of the turbulent puff observed in pipe flow transition, within which r.m.s. velocity and turbulent energy levels were highest. Turbulent fluctuations and energy levels rapidly decayed beyond this region and flow relaminarized. The acceleration of the fluid through the stenosis resulted in wall shear stress (WSS) magnitudes that exceeded upstream levels by more than a factor of 30 but low WSS levels accompanied the flow separation zones that formed immediately downstream of the stenosis. Transition to turbulence in the case of the eccentric stenosis was found to be manifested as large temporal and spatial gradients of shear stress, with significant axial and circumferential variations in instantaneous WSS.

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