An Analysis of Turbulent Shear Stresses in Leakage Flow Through a Bileaflet Mechanical Prostheses

2002 ◽  
Vol 124 (2) ◽  
pp. 155-165 ◽  
Author(s):  
Brandon R. Travis ◽  
Hwa L. Leo ◽  
Parina A. Shah ◽  
David H. Frakes ◽  
Ajit P. Yoganathan
Keyword(s):  
Pulsatile Flow ◽  
Laser Doppler Velocimetry ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Leakage Flow ◽  
Cyclic Variation ◽  
Doppler Velocimetry ◽  
Reynolds Stresses ◽  
Mechanical Prostheses ◽  
Flow Through

In this work, estimates of turbulence were made from pulsatile flow laser Doppler velocimetry measurements using traditional phase averaging and averaging after the removal of cyclic variation. These estimates were compared with estimates obtained from steady leakage flow LDV measurements and an analytical method. The results of these studies indicate that leakage jets which are free and planar in shape may be more unstable than other leakage jets, and that cyclic variation does not cause a gross overestimation of the Reynolds stresses at large distances from the leakage jet orifice.

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro

1990 ◽  
Vol 23 (12) ◽  
pp. 1231-1238 ◽  
Author(s):  
H Nygaard ◽  
M Giersiepen ◽  
J.M Hasenkam ◽  
D Westphal ◽  
P.K Paulsen ◽  
...  
Keyword(s):  
Pulsatile Flow ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Aortic Valves

An LDV Study of the Influence of the Radiator on a Cooling Module Fan

2002 ◽  
Author(s):  
Robert J. Martinuzzi ◽  
Gregory A. Kopp ◽  
Brian Havel
Keyword(s):  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Low Flow ◽  
Doppler Velocimetry ◽  
Flow Conditions ◽  
Flow Rates ◽  
Cooling Fan ◽  
Outlet Flow ◽  
Flow Through ◽  
Cooling Module

The influence of the radiator on the flow through an automotive cooling fan module was investigated using Laser Doppler Velocimetry for three different flow conditions. It is found that at the nominal design point, the radiator acts as an effective flow straightener. At low flow rates, fan induced pre-swirl is significant, but the radiator helps reduce reverse flow through the fan. Under ram air conditions the upstream inlet distortions persist through the module resulting in a highly distorted outlet flow.

Measurement by PIV of Synoptic Strain Rate Downstream of a St. Jude Prosthetic Valve

1999 ◽  
Author(s):  
L. M. Lourenco ◽  
K. J. Spellings
Keyword(s):  
Blood Cells ◽  
Cell Walls ◽  
Prosthetic Valve ◽  
Thrombus Formation ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Major Contributor ◽  
Reynolds Stresses ◽  
Flowing Blood ◽  
Biochemical Signals

Abstract It is widely accepted that shear stresses in flowing blood affect the behavior of blood cells. Effects may range from the alteration of the surface properties of platelets to damage of cell walls. These effects result in the release of biochemical signals leading to platelet aggregation and thrombus formation. While numerous studies support these observations it is still unclear what the main shear mechanisms are. However, there is large support to the notion that turbulent shear stresses (Reynolds stresses) are the major contributor to the shear experienced by blood solids.

Two-Component Laser Velocimeter Measurements Downstream of Heart Valve Prostheses in Pulsatile Flow

1986 ◽  
Vol 108 (1) ◽  
pp. 59-64 ◽  
Author(s):  
W. G. Tiederman ◽  
M. J. Steinle ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Pulsatile Flow ◽  
Turbulent Shear ◽  
Prosthetic Heart Valves ◽  
Shear Stresses ◽  
Axial Distance ◽  
Prosthetic Valves ◽  
Disk Valve ◽  
Two Component ◽  
Stress Levels

Elevated turbulent shear stresses resulting from disturbed blood flow through prosthetic heart valves can cause damage to red blood cells and platelets. The purpose of this study was to measure the turbulent shear stresses occurring downstream of aortic prosthetic valves during in-vitro pulsatile flow. By matching the indices of refraction of the blood analog fluid and model aorta, correlated, simultaneous two-component laser velocimeter measurements of the axial and radial velocity components were made immediately downstream of two aortic prosthetic valves. Velocity data were ensemble averaged over 200 or more cycles for a 15-ms window opened at peak systolic flow. The systolic duration for cardiac flows of 8.4 L/min was 200 ms. Ensemble-averaged total shear stress levels of 2820 dynes/cm2 and 2070 dynes/cm2 were found downstream of a trileaflet valve and a tilting disk valve, respectively. These shear stress levels decreased with axial distance downstream much faster for the tilting disk valve than for the trileaflet valve.

Turbulence measurements in smooth concentric annuli with small radius ratios

1975 ◽  
Vol 72 (1) ◽  
pp. 189-206 ◽  
Author(s):  
K. Rehme
Keyword(s):  
Maximum Velocity ◽  
Turbulence Models ◽  
Turbulent Energy ◽  
Small Radius ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Parallel Plates ◽  
Number Range ◽  
Flow Through ◽  
Asymmetric Flows

The structure of turbulence of fully-developed flow through three concentric annuli with small radius ratios was investigated experimentally for a Reynolds number range Re = 2 × 104−2 × 105. Turbulence intensities were measured in three directions, and turbulent shear stresses in the radial and azimuthal direction, in annuli of radius ratios α = 0·02, 0·04 and 0·1, respectively. The results showed that the structure of turbulence for these asymmetric flows is not the same as that for symmetrical flows (tubes and parallel plates). The main difference between symmetrical and asymmetric flows is that, for the latter, the diffusion of turbulent energy plays an important role. This is the reason not only for the non-coincidence of the positions of zero shear stress and maximum velocity, but also for the failure of most turbulence models in calculating asymmetric flows.

scholarly journals 5D Flow Tensor MRI to Efficiently Map Reynolds Stresses of Aortic Blood Flow In-Vivo

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jonas Walheim ◽  
Hannes Dillinger ◽  
Alexander Gotschy ◽  
Sebastian Kozerke
Keyword(s):  
Blood Flow ◽  
Heart Valve ◽  
Prosthetic Heart Valve ◽  
Low Rank ◽  
Heart Valve Disease ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Aortic Blood Flow ◽  
Reynolds Stresses

AbstractDiseased heart valves perturb normal blood flow with a range of hemodynamic and pathologic consequences. In order to better stratify patients with heart valve disease, a comprehensive characterization of blood flow including turbulent contributions is desired. In this work we present a framework to efficiently quantify velocities and Reynolds stresses in the aorta in-vivo. Using a highly undersampled 5D Flow MRI acquisition scheme with locally low-rank image reconstruction, multipoint flow tensor encoding in short and predictable scan times becomes feasible (here, 10 minutes), enabling incorporation of the protocol into clinical workflows. Based on computer simulations, a 19-point 5D Flow Tensor MRI encoding approach is proposed. It is demonstrated that, for in-vivo resolution and signal-to-noise ratios, sufficient accuracy and precision of velocity and turbulent shear stress quantification is achievable. In-vivo proof of concept is demonstrated on patients with a bio-prosthetic heart valve and healthy controls. Results demonstrate that aortic turbulent shear stresses and turbulent kinetic energy are elevated in the patients compared to the healthy subjects. Based on these data, it is concluded that 5D Flow Tensor MRI holds promise to provide comprehensive flow assessment in patients with heart valve diseases.

Reynolds Stresses and Dissipation Mechanisms Downstream of a Turbine Cascade

1987 ◽  
Vol 109 (2) ◽  
pp. 258-267 ◽  
Author(s):  
J. Moore ◽  
D. M. Shaffer ◽  
J. G. Moore
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Turbine Cascade ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Redundant Data ◽  
Fitting Procedures

An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10 percent of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The measured Reynolds stresses are combined with measured distributions of velocity to show how and where losses are being produced. The mechanisms for the dissipation of mean kinetic energy in this swirling three-dimensional flow are revealed.

Analysis of Transitional and Turbulent Flow Through the FDA Benchmark Nozzle Model Using Laser Doppler Velocimetry

2016 ◽  
Vol 7 (3) ◽  
pp. 191-209 ◽  
Author(s):  
Joshua O. Taylor ◽  
Bryan C. Good ◽  
Anthony V. Paterno ◽  
Prasanna Hariharan ◽  
Steven Deutsch ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Laser Doppler Velocimetry ◽  
Laser Doppler ◽  
Doppler Velocimetry ◽  
Flow Through
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