Influence of Cardiac Flow Rate on Turbulent Shear Stress from a Prosthetic Heart Valve

1988 ◽  
Vol 110 (2) ◽  
pp. 123-128 ◽  
Author(s):  
A. C. Schwarz ◽  
W. G. Tiederman ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Time Window ◽  
Prosthetic Heart Valve ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Straight Tube ◽  
Blood Constituents ◽  
Turbulent Shear Stress ◽  
Disk Valve

Elevated turbulent shear stresses associated with sufficient exposure times are potentially damaging to blood constituents. Since these conditions can be induced by mechanical heart valves, the objectives of this study were to locate the maximum turbulent shear stress in both space and time and to determine how the maximum turbulent shear stress depends on the cardiac flow rate in a pulsatile flow downstream of a tilting disk valve. Two-component, simultaneous, correlated laser velocimeter measurements were recorded at four different axial locations and three different flow rates in a straight tube model of the aorta. All velocity data were ensemble averaged within a 15 ms time window located at approximately peak systolic flow over more than 300 cycles. Shear stresses as high as 992 dynes/cm2 were found 0.92 tube diameters downstream of the monostrut, disk valve. The maximum turbulent shear stress was found to scale with flow rate to the 0.72 power. A repeatable starting vortex was shed from the disk at the beginning of each cycle.

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.

Cyclic flow characteristics in an idealized asymmetric abdominal aortic aneurysm model

2003 ◽  
Vol 217 (1) ◽  
pp. 27-39 ◽  
Author(s):  
T H Yip ◽  
S C M Yu
Keyword(s):  
Shear Stress ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Cyclic Flow ◽  
Turbulent Shear Stress ◽  
Abdominal Aortic ◽  
Flow Cycle

The flow characteristics and the corresponding hydrodynamic stability in an idealized asymmetric abdominal aortic aneurysm (AAA) model have been investigated using a laser Doppler anemometer. A rectified sine waveform was used to simulate aortic flow conditions (Reδ = 806 and α = 12.2). The flow around the distal neck of the AAA model undergoes transition and becomes turbulent for a fraction of time shortly after the commencement of the deceleration phases at every flow cycle while the rest of the flow inside the model stayed laminar throughout the cycle. As a result of non-symmetric vortical structure development inside the model, the distribution of turbulent shear stresses was found to be highly uneven along the radial direction of the model; this is in contrast to results found by the present authors in the symmetrical AAA model. The maximum turbulent shear stress found at the straight side of the distal neck are four times more than the maximum turbulent shear stress measured at the most dilated side of the distal neck. One of the interesting biological implications of the results is that the outward dilation of the arterial wall may be a physiological response to avoid the high turbulent shear load from the momentarily turbulent blood flow.

Effect of Tilting Disk, Heart Valve Orientation on Flow Through a Curved Aortic Model

1989 ◽  
Vol 111 (3) ◽  
pp. 228-232 ◽  
Author(s):  
J. D. Walker ◽  
W. G. Tiederman ◽  
W. M. Phillips
Keyword(s):  
Shear Stress ◽  
Laser Doppler Velocimeter ◽  
Turbulent Shear ◽  
Human Aorta ◽  
Radius Of Curvature ◽  
Turbulent Shear Stress ◽  
Disk Valve ◽  
Stress Levels ◽  
Flow Through ◽  
Peak Value

The influence of tilting disk valve orientation on pulsatile flow through a curved tube model of the human aorta was studied. Simultaneous, two-component laser Doppler velocimeter measurements were made in a tube having a 22 mm diameter and 41 mm radius of curvature which simulated the average dimensions of the adult aorta. The blood analog fluid had a viscosity of 3.0 cp and matched the refractive index of the glass model aorta. Results at mid-arch showed low turbulence levels in early systole and no influence of valve orientation. During mid-systole, fluid from the ventricle reached mid-arch exhibiting strong influence of valve orientation and increased turbulence levels. With the major orifice of the valve adjacent to the inner curved wall, the peak turbulent shear stress was 307 dynes/cm2 at mid-arch during mid-systole. When the major orifice was rotated 180 degrees, the peak value was reduced to 91 dynes/cm2 at the same location and time. At the exit of the curved section, the flow was independent of the valve orientation and the turbulent shear stress levels were an order of magnitude lower than the peak value at the inlet. This study demonstrated that orienting the major orifice of a tilting disk valve adjacent to the outer curved wall minimized turbulent shear stress levels.

Impact of fluid turbulent shear stress on failure surface of reservoir bank landslide

2018 ◽  
Vol 11 (22) ◽  
Author(s):  
Xuan Zhang ◽  
Liang Chen ◽  
Faming Zhang ◽  
Chengteng Lv ◽  
Yi feng Zhou
Keyword(s):  
Shear Stress ◽  
Failure Surface ◽  
Turbulent Shear ◽  
Turbulent Shear Stress

INFLUENCE OF FLOW RATE AND AXIAL POSITION ON SHEAR STRESSES

2004 ◽  
Vol 04 (01) ◽  
pp. 71-75
Author(s):  
ALI A. SAKHAEIMANESH
Keyword(s):  
Flow Rate ◽  
Artificial Heart ◽  
Heart Valves ◽  
Direct Relationship ◽  
Axial Position ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Close Vicinity ◽  
Velocity Gradients ◽  
Artificial Heart Valves

To locate the maximum and mean turbulent shear stresses in both time and space, and to determine how shear stresses depend on the flow rate and downstream measuring planes of the artificial heart valves, this study was carried out. Maximum and mean turbulent shear stresses estimated at 0.5D downstream of the valves showed a direct relationship with flow rate both in the Jellyfish and St. Vincent valves. The magnitude of both mean and maximum shear stresses in the Jellyfish valve was found to be higher than that of the St. Vincent valve at 0.5 and 1D downstream of the Jellyfish valve. Maximum shear stresses were found in close vicinity to the valve where highly disturbed flow with steep velocity gradients were observed.

Contribution towards a Reynolds-stress closure for low-Reynolds-number turbulence

1976 ◽  
Vol 74 (4) ◽  
pp. 593-610 ◽  
Author(s):  
K. Hanjalić ◽  
B. E. Launder
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Reynolds Stress ◽  
Dissipation Rate ◽  
Numerical Solutions ◽  
Low Reynolds Number ◽  
Transport Processes ◽  
Turbulent Shear ◽  
Turbulent Shear Stress ◽  
Low Reynolds

The problem of closing the Reynolds-stress and dissipation-rate equations at low Reynolds numbers is considered, specific forms being suggested for the direct effects of viscosity on the various transport processes. By noting that the correlation coefficient$\overline{uv^2}/\overline{u^2}\overline{v^2} $is nearly constant over a considerable portion of the low-Reynolds-number region adjacent to a wall the closure is simplified to one requiring the solution of approximated transport equations for only the turbulent shear stress, the turbulent kinetic energy and the energy dissipation rate. Numerical solutions are presented for turbulent channel flow and sink flows at low Reynolds number as well as a case of a severely accelerated boundary layer in which the turbulent shear stress becomes negligible compared with the viscous stresses. Agreement with experiment is generally encouraging.

Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 28-37 ◽  
Author(s):  
Ralph J. Volino ◽  
Michael P. Schultz ◽  
Christopher M. Pratt
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Streamwise Velocity ◽  
Turbulent Shear ◽  
Conditional Sampling ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Transitional Boundary Layer ◽  
Turbulent Shear Stress ◽  
Order Of Magnitude

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.

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