Numerical Study of the Steady Axisymmetric Flow Through a Disk-Type Prosthetic Heart Valve in a Constant Diameter Chamber

1977 ◽  
Vol 99 (2) ◽  
pp. 91-97 ◽  
Author(s):  
F. N. Underwood ◽  
T. J. Mueller
Keyword(s):  
Shear Stress ◽  
Heart Valve ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Reverse Flow ◽  
Axisymmetric Flow ◽  
Prosthetic Heart Valve ◽  
High Shear ◽  
Flow Through ◽  
Very High

Numerical solutions for the steady axisymmetric flow through a disk-type prosthetic heart valve were obtained for Reynolds numbers from 20 to 1300. Stream function, vorticity, and shear and normal stress plots are presented. Comparison of the length of the separated flow region downstream of the disk with experimental data shows good agreement through Reynolds number 500. The maximum value of the shear stress occurred on the upstream corner of the disk. These detailed results clearly identify regions of very high shear and normal stresses (erythrocyte deformation or damage), regions of very low or very high shear stress at walls (atheromatous lesions), and the extent of separated or reverse flow regions (thrombosis).

Numerical Study of the Steady Axisymmetric Flow Through a Disk-Type Prosthetic Heart Valve in an Aortic-Shaped Chamber

1979 ◽  
Vol 101 (3) ◽  
pp. 198-204 ◽  
Author(s):  
F. N. Underwood ◽  
T. J. Mueller
Keyword(s):  
Shear Stress ◽  
Heart Valve ◽  
Stream Function ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Axisymmetric Flow ◽  
Prosthetic Heart Valve ◽  
High Shear ◽  
Flow Through ◽  
Very High

Numerical solutions for the steady axisymmetric flow through a disk-type prosthetic heart valve were obtained for Reynolds numbers from 50 to 600. A nonuniform mesh in both directions was used and the finite difference equations in vorticity and stream function were solved explicitly. Stream function, vorticity, and shear and normal stress plots are presented. These detailed results clearly identify regions of very high shear and normal stresses, regions of very low or very high shear stress at the walls and the extent of separated or reverse flow regions. The length of the separated flow region downstream of the disk agreed very well with experimental data. The maximum value of the shear stress occurred on the upstream corner of the disk.

Numerical Study on Diastolic Left Ventricular Hemodynamics Using Motion Models of Mitral Valve With/Without Edge-to-Edge Repair

2010 ◽  
Author(s):  
Yingying Hu ◽  
Liang Shi ◽  
Siva Parameswaran ◽  
Sergey A. Smirnov ◽  
Zhaoming He
Keyword(s):  
Shear Stress ◽  
Mitral Valve ◽  
Left Ventricle ◽  
Platelet Activation ◽  
Numerical Study ◽  
Left Ventricular ◽  
High Shear ◽  
High Shear Stress ◽  
Orifice Area ◽  
Motion Models

Edge-to-edge repair (ETER) is a newly developed technique to correct such mitral valve (MV) malfunctions as regurgitation [1,2]. This technique changes MV geometric configuration by suturing the anterior and posterior leaflets at central or commissural edges, and consequently alters MV and left ventricle (LV) dynamics. For instance, stress in the MV elevated due to ETER may cause leaflets tearing near suture. Little has been known about shear stress on the MV and LV walls under MV ETER conditions, where high shear stress might cause platelet activation or hemolysis [3]. When ETER is done at the central leaflet edges, it generates two MV orifices, leads to two deflected jets, and completely changes vortices in the LV. ETER also reduces the orifice area, and increases jet velocity and transmitral pressure [1,2,4]. Flow patterns in the LV and ETER effects on the LV and MV functions have not been understood well.

Numerical Solutions of the Navier-Stokes Equations for Axisymmetric Flows

1968 ◽  
Vol 10 (5) ◽  
pp. 389-401 ◽  
Author(s):  
D. R. Strawbridge ◽  
G. T. J. Hooper
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Axisymmetric Flow ◽  
Labyrinth Seal ◽  
Taylor Vortex ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Taylor Vortex Flow ◽  
Concentric Cylinders ◽  
Flow Through

A numerical method is presented for the solution of the time dependent Navier-Stokes equations for the axisymmetric flow of an incompressible viscous fluid. The method is applied to the problems of Taylor-vortex flow about an enclosed rotating cylinder and between infinite concentric cylinders, and to the analysis of the flow through a labyrinth seal. The torque calculations, which show favourable agreement with experiment, and the resulting flow patterns are presented graphically.

Measurement of the viscosity of supercooled liquids at high shear rates with a Hopkinson torsion bar

1982 ◽  
Vol 381 (1780) ◽  
pp. 195-214 ◽  
Keyword(s):  
Shear Stress ◽  
High Pressures ◽  
Rolling Contact ◽  
Shear Strain Rate ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Short Time ◽  
Torsion Bar ◽  
Very High

The Eyring theory of viscous flow suggests that lubricating oils should exhibit shear thinning when the shear stress exceeds about 5 MPa. The results of friction experiments in rolling-contact disc machines where very high pressures are generated in the lubricant film support this prediction, but are open to the criticism that the fluid is subjected to a high pressure for such a short time ( ca . 10 -4 s) that an equilibrium state may not be reached. In the present investigation the appropriate condition of the lubricant is achieved, not by subjecting it to very high pressures but by maintaining it in the supercooled state. The lubricant is thus in a condition of equili­brium and the shear experiments are carried out at atmospheric pressure. The lubricant specimen is retained in a suitably adapted split Hopkinson torsion bar, and at the high rates of shear applied ( ca . 10 4 s -1 ) the shear stress at sufficiently low temperatures can exceed 5 MPa. By this tech­nique the shear pulse is applied for a sufficiently short time ( ca . 10 -3 s) to avoid viscous heating of the sample, which bedevils normal viscometry at high shear rates. Two fluids were tested: polyphenyl ether 5P4E and a mineral oil Shell HVI 650. Nonlinearity in the shear-stress-shear-strain-rate relation was found when the stress exceeded about 3 MPa. The elastic shear modulus G ∞ was also measured, yielding ca . 500 MPa for 5P4E and ca . 50 MPa for HVI 650.These values compare with ca . 1100 MPa and 300 MPa as found by the high-frequency oscillating shear technique at small strains.

Influence of Distal Stenosis on Blood Flow Through Coronary Serial Stenoses: A Numerical Study

2019 ◽  
Vol 16 (03) ◽  
pp. 1842003 ◽  
Author(s):  
Biyue Liu ◽  
Dalin Tang
Keyword(s):  
Blood Flow ◽  
Pressure Drop ◽  
Numerical Study ◽  
Reverse Flow ◽  
Arterial Segment ◽  
Disturbed Flow ◽  
Curved Artery ◽  
Artery Segment ◽  
Flow Through ◽  
Drop Flow

Computer simulations of the blood flow through right coronary arteries with two stenoses in the same arterial segment are carried out to investigate the interactions of serial stenoses, especially the effect of the distal stenosis. Various mathematical models are developed by varying the location of the distal stenosis. The numerical results show that the variation of the distal stenosis has significant impact on coronary hemodynamics, such as the pressure drop, flow shifting, wall shear stress and flow separation. Our simulations demonstrate that the distal stenosis has insignificant effect on the disturbed flow pattern in the regions of upstream and across the proximal stenosis. In a curved artery segment with two moderate stenoses of the same size, the distal stenosis causes a larger pressure drop and a more disturbed flow field in the poststenotic region than the proximal stenosis does. A distal stenosis located at a further downstream position causes a larger pressure drop and a stronger reverse flow.

Shear stress experienced by echinoderm eggs in the oviduct during spawning: potential role in the evolution of egg properties

1999 ◽  
Vol 202 (22) ◽  
pp. 3111-3119 ◽  
Author(s):  
F.I. Thomas ◽  
T.F. Bolton
Keyword(s):  
Shear Stress ◽  
Laminar Flow ◽  
Potential Role ◽  
Shear Stresses ◽  
High Shear ◽  
High Shear Stress ◽  
Arbacia Punctulata ◽  
Shear Rates ◽  
Flow Through

Shear stresses experienced by eggs in the oviduct of the echinoid Arbacia punctulata during spawning were calculated using engineering equations that describe laminar flow through pipes. Shear stresses in the oviduct ranged from 0 to 58.7 Pa. Two properties of eggs were identified that have the potential either to minimize the shear stress in the oviduct or to reduce the damage experienced by eggs exposed to high shear stress. These properties are the viscosity of the eggs and the presence of extracellular layers on eggs of A. punctulata. The viscosity of eggs decreases with increasing shear rates, which reduces the magnitude of shear stress experienced in the oviduct, while the extracellular layers mitigate the effect of shear stress on the eggs. Eggs with intact extracellular layers were damaged less frequently than were those with the extracellular layers removed. The results of this research indicate that physical stresses may be important selective factors in the evolution of gamete properties.

Experimental and Numerical Study of Three-Dimensional Flows in a Mixed-Flow Pump Stage

1994 ◽  
Author(s):  
T. Takemura ◽  
A. Goto
Keyword(s):  
Numerical Study ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Swirl Flow ◽  
Experimental Results ◽  
Test Fluid ◽  
Internal Flows ◽  
Mixed Flow ◽  
Pump Stage ◽  
Flow Through

Internal flows of a low specific speed pump stage, having a mixed-flow impeller and a vaned bowl diffuser combination, have been investigated experimentally and numerically. Air was used as the test fluid, and the internal flows were measured at various locations and under various capacities. Flow calculations were made, for both the isolated impeller case and the complete stage case, using Denton viscous codes LOSS3D and MULTSTAGE14, by which the three-dimensional steady flow through multiple blade rows can be calculated using the inter-row mixing process. Experimental results showed the effects of the interaction between the impeller and the reverse flow, originating in the downstream diffuser, even at the design point capacity. While an impeller exit reverse flow occurred at the shroud side in the isolated impeller calculation, it was observed at the hub side in the complete stage case, showing good agreement with the experimental results. Although the flow in the diffuser was highly distorted due to a strong swirl flow, patterns of total pressure distribution could be well predicted by the complete stage calculation.

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