Evaluation of Magnetic Resonance Velocimetry for Steady Flow

1990 ◽  
Vol 112 (4) ◽  
pp. 464-472 ◽  
Author(s):  
D. N. Ku ◽  
C. L. Biancheri ◽  
R. I. Pettigrew ◽  
J. W. Peifer ◽  
C. P. Markou ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Steady Flow ◽  
Laser Doppler Anemometry ◽  
Flow Behavior ◽  
Velocity Profiles ◽  
Secondary Flows ◽  
Whole Body ◽  
Straight Tube ◽  
Flow Conditions ◽  
Wide Range

Whole body magnetic resonance (MR) imaging has recently become an important diagnostic tool for cardiovascular diseases. The technique of magnetic resonance phase velocity encoding allows the quantitative measurement of velocity for an arbitrary component direction. A study was initiated to determine the ability and accuracy of MR velocimetry to measure a wide range of flow conditions including flow separation, three-dimensional secondary flow, high velocity gradients, and turbulence. A steady flow system pumped water doped with manganese chloride through a variety of test sections. Images were produced using gradient echo sequences on test sections including a straight tube, a curved tube, a smoothly converging-diverging nozzle, and an orifice. Magnetic resonance measurements of laminar and turbulent flows were depicted as cross-sectional velocity profiles. MR velocity measurements revealed such flow behavior as spatially varying velocity, recirculation and secondary flows over a wide range of conditions. Comparisons made with published experimental laser Doppler anemometry measurements and theoretical calculations for similar flow conditions revealed excellent accuracy and precision levels. The successful measurement of velocity profiles for a variety of flow conditions and geometries indicate that magnetic resonance imaging is an accurate, non-contacting velocimeter.

Comparison of Experimental and Numerical Simulations of Flow Within an Arterio-Venous Graft

2000 ◽  
Author(s):  
Paul F. Fischer ◽  
Seung Lee ◽  
Francis Loth ◽  
Hisham S. Bassiouny ◽  
Nurullah Arslan
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Laser Doppler Anemometry ◽  
Transition To Turbulence ◽  
Flow Conditions ◽  
Venous Graft ◽  
Venous Anastomosis ◽  
Av Graft ◽  
Good Agreement

Abstract This was a study to compare computational and experimental results of flow field inside the venous anastomosis of an arteriovenous (AV) graft. Laser Doppler anemometry (LDA) measurements were conducted inside an upscaled end-to-side graft model under steady flow conditions at Reynolds number 1820 which is representative of the in vivo flow conditions inside a human AV graft. The distribution of the velocity and turbulence intensity was measured at several locations in the plane of the bifurcation. This flow field was simulated using computation fluid dynamics (CFD) and shown to be in good agreement. Under steady flow conditions, the flow field demonstrated an unsteady character (transition to turbulence).

Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Colin D. Copeland ◽  
Ricardo Martinez-Botas ◽  
Martin Seiler
Keyword(s):  
Steady Flow ◽  
Flow Behavior ◽  
Turbine Rotor ◽  
Flow Conditions ◽  
Turbine Performance ◽  
Pulsed Flow ◽  
Performance Map ◽  
Engine Operating Condition ◽  
Double Entry ◽  
The Impact

Circumferentially divided, double entry turbocharger turbines are designed with a dividing wall parallel to the machine axis such that each entry feeds a separate 180 deg section of the nozzle circumference prior to entry into the rotor. This allows the exhaust pulses originating from the internal combustion exhaust to be preserved. Since the turbine is fed by two separate unsteady flows, the phase difference between the exhaust pulses entering the turbine rotor will produce a momentary imbalance in the flow conditions around the periphery of the turbine rotor. This research seeks to provide new insight into the impact of unsteadiness on turbine performance. The discrepancy between the pulsed flow behavior and that predicted by a typical steady flow performance map is a central issue considered in this work. In order to assess the performance deficit attributable to unequal admission, the steady flow conditions introduced in one inlet were varied with respect to the other. The results from these tests were then compared with unsteady, in-phase and out-of-phase pulsed flows most representative of the actual engine operating condition.

An In Vitro Comparative Study of St. Jude Medical and Edwards-Duromedics Bileaflet Valves Using Laser Anemometry

1989 ◽  
Vol 111 (4) ◽  
pp. 298-302 ◽  
Author(s):  
R. Fatemi ◽  
K. B. Chandran
Keyword(s):  
Comparative Study ◽  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Velocity Profiles ◽  
Flow Conditions ◽  
Tilt Axis ◽  
Jude Medical ◽  
Laser Anemometry ◽  
Bileaflet Valves

An in vitro comparative study of St. Jude (SJ) and Edwards-Duromedics (DM) Bileaflet valves was performed under steady and physiological pulsatile flow conditions in an axisymmetric chamber using Laser Doppler Anemometry (LDA). LDA measurements were conducted in two different orientations; in the first orientation, the LDA traverse was perpendicular and, in the second orientation, parallel to the tilt axis of the leaflets. The axial velocities were measured in both orientations at two different locations distal to the valves. The velocity profiles at peak systole show the presence of stronger vortex in the sinus region for flow past SJ valve in the first orientation compared to the DM valve. Velocity profile distal to the SJ valve in second orientation was relatively flat where as for the DM valve, a jet-like flow was present. The differences found in the velocity profiles between the two valves can be attributed to the differences in geometry with thicker leaflets, smaller angle of leaflets opening and the presence of the leaflet curvature for the DM valve. The results obtained in this study do not show any fluid dynamic advantages due to the curved leaflet geometry of the DM valve.

scholarly journals Numerical and physical modeling of water flow over the ogee weir of the new Niedów barrage

2016 ◽  
Vol 64 (1) ◽  
pp. 67-74 ◽  
Author(s):  
Oscar Herrera-Granados ◽  
Stanisław W. Kostecki
Keyword(s):  
Experimental Data ◽  
Numerical Modeling ◽  
Steady Flow ◽  
Water Flow ◽  
Physical Modeling ◽  
Numerical Models ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Conditions ◽  
Low Head

Abstract In this paper, two- and three-dimensional numerical modeling is applied in order to simulate water flow behavior over the new Niedów barrage in South Poland. The draining capacity of one of the flood alleviation structures (ogee weir) for exploitation and catastrophic conditions was estimated. In addition, the output of the numerical models is compared with experimental data. The experiments demonstrated that the draining capacity of the barrage alleviation scheme is sufficiently designed for catastrophic scenarios if water is flowing under steady flow conditions. Nevertheless, the new cofferdam, which is part of the temporal reconstruction works, is affecting the draining capacity of the whole low-head barrage project.

The Impedance of Curved Artery Models

1983 ◽  
Vol 105 (3) ◽  
pp. 275-282 ◽  
Author(s):  
S. G. Kang ◽  
J. M. Tarbell
Keyword(s):  
Aortic Arch ◽  
Steady Flow ◽  
Flow Rate ◽  
Straight Tube ◽  
Flow Conditions ◽  
Mean Flow ◽  
Periodic Flows ◽  
Curved Artery ◽  
Flow Impedance ◽  
Drop Flow

The impedance (pressure drop/flow rate) of four curved artery models has been determined experimentally for steady and periodic flows simulating conditions in the aortic arch. Steady flow results indicate that very short entry lengths are required for flow development in curved artery models, and impedance is elevated above straight tube values by a factor of 3–4 for mean flow conditions in the aortic arch. Results for periodic flow with a nonzero mean show a significant elevation of mean flow impedance relative to values for steady flow at the mean flow rate—a factor of 2–3 for aortic arch flow conditions. The impedance of the first harmonic of periodic flows follows straight tube theory at high values of the unsteadiness parameter in agreement with available theory for curved tubes. The implications of the impedance measurements for wall shear stress in the aortic arch are discussed.

Characterization of Transition to Turbulence for Blood in a Straight Pipe Under Steady Flow Conditions

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Dipankar Biswas ◽  
David M. Casey ◽  
Douglas C. Crowder ◽  
David A. Steinman ◽  
Yang H. Yun ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Steady Flow ◽  
Newtonian Fluid ◽  
Fluid Velocity ◽  
Shear Thinning ◽  
Velocity Profiles ◽  
Transition To Turbulence ◽  
Pipe Diameter ◽  
Flow Conditions ◽  
Straight Pipe

Blood is a complex fluid that, among other things, has been established to behave as a shear thinning, non-Newtonian fluid when exposed to low shear rates (SR). Many hemodynamic investigations use a Newtonian fluid to represent blood when the flow field of study has relatively high SR (>200 s−1). Shear thinning fluids have been shown to exhibit differences in transition to turbulence (TT) compared to that of Newtonian fluids. Incorrect prediction of the transition point in a simulation could result in erroneous hemodynamic force predictions. The goal of the present study was to compare velocity profiles near TT of whole blood and Newtonian blood analogs in a straight rigid pipe with a diameter 6.35 mm under steady flow conditions. Rheology was measured for six samples of whole porcine blood and three samples of a Newtonian fluid, and the results show blood acts as a shear thinning non-Newtonian fluid. Measurements also revealed that blood viscosity at SR = 200 s−1 is significantly larger than at SR = 1000 s−1 (13.8%, p < 0.001). Doppler ultrasound (DUS) was used to measure velocity profiles for blood and Newtonian samples at different flow rates to produce Reynolds numbers (Re) ranging from 1000 to 3300 (based on viscosity at SR = 1000 s−1). Two mathematically defined methods, based on the velocity profile shape change and turbulent kinetic energy (TKE), were used to detect TT. Results show similar parabolic velocity profiles for both blood and the Newtonian fluid for Re < 2200. However, differences were observed between blood and Newtonian fluid velocity profiles for larger Re. The Newtonian fluid had blunt-like velocity profiles starting at Re = 2403 ± 8 which indicated transition. In contrast, blood did not show this velocity profile change until Re = 2871 ± 104. The Newtonian fluid had large velocity fluctuations (root mean square (RMS) > 20%) with a maximum TKE near the pipe center at Re = 2316 ± 34 which indicated transition. In contrast, blood results showed the maximum TKE at Re = 2806 ± 109. Overall, the critical Re was delayed by ∼20% (p < 0.001) for blood compared to the Newtonian fluid. Thus, a Newtonian assumption for blood at flow conditions near transition could lead to large errors in velocity prediction for steady flow in a straight pipe. However, these results are specific to this pipe diameter and not generalizable since SR is highly dependent on pipe diameter. Further research is necessary to understand this relation in different pipe sizes, more complex geometries, and under pulsatile flow conditions.

A Mathematical Model for Dispersion in the Direction Of Flow in Porous Media

1963 ◽  
Vol 3 (01) ◽  
pp. 49-52 ◽  
Author(s):  
H.A. Deans
Keyword(s):  
Porous Media ◽  
Diffusion Equation ◽  
Molecular Diffusion ◽  
Fixed Bed ◽  
Porous Matrix ◽  
Velocity Profiles ◽  
Transport Processes ◽  
Longitudinal Dispersion ◽  
Flow Conditions ◽  
Wide Range

Introduction The problem of multicomponent single-phase flow through porous media is encountered in the study of petroleum reservoirs, gas chromatographic and ion-exchange columns, industrial fixed-bed contacters and elsewhere. These particular examples span the wide range of flow conditions possible; Reynolds numbers of less than 10 are not unusual in oil-production problems, while values in excess of 10 are common in large fixed-bed operations. The study of flow-dependent transport phenomena is complicated both by the changes in the character of the flow over this range, and by the irregularity of the flow boundaries inherent to porous media.Dispersion is one of the important phenomena known to depend fundamentally on flow conditions as well as on fluid and medium properties. As used in this paper, the term "dispersion" refers to the observed mixing of fluid elements of different composition which occurs in flow systems. The actual mechanism may be one or more of a number listed below. Only dispersion in the direction of the mean flow (referred to as axial or longitudinal dispersion (or mixing) is considered here, although lateral dispersion arises as part of certain coupled mechanisms. MECHANISMS FOR LONGITUDINAL DISPERSION A number of distinct mechanisms are known to contribute to the phenomenon of longitudinal dispersion. The more important of these are as follows.Molecular diffusion in the flow direction.Turbulent (cell) mixing.Lateral transport processes coupled with velocity and/or residence time distributions, including:"Taylor" diffusion caused by the interaction of velocity profiles in individual voids with lateral molecular diffusion;separation and remixing or interdiffusion of streams having different velocities around particles; andthe coupling of gross velocity profiles, caused by viscous instability or inhomogeneous porosity, with lateral dispersion.Finite mass-transfer rate between a porous matrix and the flowing phase, and finite diffusion rate inside elements of the porous matrix. It is a well documented fact that these mechanisms, whether acting individually or in combinations, produce essentially similar integral effects. The observed dispersion can be described approximately by solutions of the diffusion equation with a properly chosen dispersion coefficient.Necessary conditions for equivalence between dispersion and diffusion are discussed by Klinkenberg and Sjenitzer. Apparently these conditions are not satisfied exactly in many real systems. "Best fit" solutions of the diffusion equation often depart appreciably from measured breakthrough curves for the usual pulse- or step-forced experimental systems. In particular, pulse response curves usually show some degree of asymmetry and "tailing" which cannot be reproduced by the one-parameter diffusion model.The three-parameter model proposed herein attempts to produce these effects in a realistic manner. A symmetry and tailing are predicted for certain sets of parameter values, while for other sets the new model agrees with the diffusion model. VELOCITY DEPENDENCE OF DISPERSION Molecular diffusion apparently controls at sufficiently low Reynolds number in both gas and liquid systems. At Re greater than 20, turbulent cell mixing is dominant for gases flowing at low pressure; the data of McHenry and Wilhelms show that the mixing cell is approximately 1 particle diameter long in random sphere packs. SPEJ P. 49^

Large Eddy Simulations of a Turbocharger Radial Turbine Under Pulsating Flow Conditions

2021 ◽  
Author(s):  
Roberto Mosca ◽  
Shyang Maw Lim ◽  
Mihai Mihaescu
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Secondary Flows ◽  
Pressure Side ◽  
Flow Conditions ◽  
Radial Turbine ◽  
Characteristic Flow ◽  
Pulse Cycle ◽  
Large Eddy ◽  
Flow Feature

Abstract The pulsating flow conditions which a turbocharger turbine is exposed cause important deviations of the turbine aerodynamic performance when compared to steady flow conditions. Indeed, the secondary flows developing in the turbine are determined by the inflow aerodynamic conditions, which largely vary during the pulse cycle. In this paper, a high-resolved Large Eddy Simulation is performed to investigate and characterize the flow field evolution in a turbocharger radial turbine over the pulse cycle. At first, the model is validated against experimental results obtained in gas-stand flow conditions. Then, the instantaneous flow field at the rotor mid-span section is compared to the one given by the equivalent cycle-averaged steady flow conditions. The results highlight five distinct flow features. At low mass flow rates, when the relative inflow angle assumes large negative values, the flow separates at the blade pressure side, causing a secondary flow consisting in two counter-rotating vortices characterized by a diameter comparable to the blade passage. As the mass flow rate increases, the first vortex persists at the blade tip while the second one moves closer to the blade trailing edge. This corresponds to the second characteristic flow field. With increasing relative inflow angle, for the third characteristic flow feature, only the recirculation at the blade leading edge is displayed and its size gradually reduces. For the fourth characteristic flow feature, at moderate negative values of the relative inflow angle, the flow field is well aligned with the blade profile and free of secondary flows. Then, as the relative inflow angle gradually grows towards large positive values, the flow separates on the blade suction side causing the mixing of the flow with the stream flowing on the pressure side of the previous blade.

Age- and sex-related bone uptake of Tc-99m-HDP measured by whole-body bone scanning

2000 ◽  
Vol 39 (05) ◽  
pp. 127-132 ◽  
Author(s):  
Nicole Sieweke ◽  
K. H. Bohuslavizki ◽  
W. U. Kampen ◽  
M. Zuhayra ◽  
M. Clausen ◽  
...  
Keyword(s):  
Whole Body ◽  
Bone Lesions ◽  
Men And Women ◽  
Bone Uptake ◽  
Normal Bone ◽  
Age Related ◽  
Number Of Patients ◽  
Wide Range ◽  
Bone Scans ◽  
Body Bone

Summary Aim of this study was to validate a recently introduced new and easy-to-perform method for quantifying bone uptake of Tc-99m-labelled diphosphonate in a routine clinical setting and to establish a normal data base for bone uptake depending on age and gender. Methods: In 49 women (14-79 years) and 47 men (6-89 years) with normal bone scans as well as in 49 women (33-81 years) and 37 men (27-88 years) with metastatic bone disease whole-body bone scans were acquired at 3 min and 3-4 hours p.i. to calculate bone uptake after correction for both urinary excretion and soft tissue retention. Results: Bone uptake values of various age-related subgroups showed no significant differences between men and women (p >0.05 ). Furthermore, no differences could be proven between age-matched subgroups of normals and patients with less than 10 metastatic bone lesions, while patients with wide-spread bone metastases revealed significantly increased uptake values. In both men and women highest bone uptake was obtained (p <0.05 ) in subjects younger than 20 years with active epiphyseal growth plates. In men, bone uptake slowly decreased with age up to 60 years and then showed a tendency towards increasing uptake values. In women, the mean uptake reached a minimun in the decade 20-29 years and then slowly increased with a positive linear correlation of age and uptake in subjects older than 55 years (r = 0.57). Conclusion: Since the results proposed in this study are in good agreement with data from literature, the new method used for quantification could be validated in a large number of patients. Furthermore, age- and sexrelated normal bone uptake values of Tc-99m-HDP covering a wide range of age could be presented for this method as a basis for further studies on bone uptake.

Role of Cardiac MRI in Detecting Familial Hypertrophic Cardiomyopathy: Review

2016 ◽  
Vol 1 (1) ◽  
pp. 4
Author(s):  
Marymol Koshy ◽  
Bushra Johari ◽  
Mohd Farhan Hamdan ◽  
Mohammad Hanafiah
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Magnetic Resonance ◽  
Genetic Disorder ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Non Invasive ◽  
Wide Range ◽  
Proper Diagnosis ◽  
Magnetic Resonance Imaging Mri ◽  
Potential Use

Hypertrophic cardiomyopathy (HCM) is a global disease affecting people of various ethnic origins and both genders. HCM is a genetic disorder with a wide range of symptoms, including the catastrophic presentation of sudden cardiac death. Proper diagnosis and treatment of this disorder can relieve symptoms and prolong life. Non-invasive imaging is essential in diagnosing HCM. We present a review to deliberate the potential use of cardiac magnetic resonance (CMR) imaging in HCM assessment and also identify the risk factors entailed with risk stratification of HCM based on Magnetic Resonance Imaging (MRI).

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