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 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 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.

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.

Simulations of Flow Through Bileaflet Mechanical Heart Valves With Asymmetric Leaflet Motion

2012 ◽  
Author(s):  
B. Min Yun ◽  
Lakshmi P. Dasi ◽  
Cyrus K. Aidun ◽  
Ajit P. Yoganathan
Keyword(s):  
Heart Valve ◽  
Heart Valves ◽  
Mechanical Heart Valve ◽  
Prosthetic Heart Valve ◽  
Prosthetic Heart Valves ◽  
Thromboembolic Events ◽  
Complex Flow ◽  
Blood Damage ◽  
Flow Through ◽  
Leaflet Motion

Prosthetic heart valves have been used for over 50 years to replace diseased native valves but still lead to severe complications such as platelet aggregation and thromboembolic events. The most widely implanted design is the bileaflet mechanical heart valve (BMHV). Most modern BMHV designs have better flow hemodynamics and blood damage performance than earlier-generation counterparts. However, blood element trauma and thromboembolic events still remain as major complications of current BMHV designs. These problems have been linked to blood damage caused by non-physiological stresses. These stresses are caused by the complex flow fields that arise due to prosthetic heart valve design. In order to reduce the severity of these complications, the blood damage that occurs in flows through prosthetic heart valves must be well understood.

Two-dimensional generalized non-Newtonian EHL lubrication: Shear rate-based solution versus shear stress-based solution

2021 ◽  
pp. 135065012110504
Author(s):  
Hai Chao Liu ◽  
Bin Bin Zhang ◽  
Volker Schneider ◽  
C.H. Venner ◽  
G. Poll
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Film Thickness ◽  
Numerical Solutions ◽  
Point Contact ◽  
Shear Thinning ◽  
High Shear ◽  
Two Dimensional ◽  
Ehl Lubrication ◽  
Ehl Contact

Lubricant behaves non-Newtonian at high shear stress and high shear rate. The non-Newtonian shear behavior of oil such as shear-thinning, viscoelasticity, and limiting shear stress could have influences on almost all characteristics of an elastohydrodynamic lubrication (EHL) contact, that is, the central film thickness, the coefficient of friction, and the temperature rise in the lubricating film. For example, for lubricants of large molecular weight or of polymer blended ones, there can be inlet shear-thinning, which would reduce the EHL film thickness. For the EHL traction in a rolling/sliding EHL contact, it cannot be reasonably predicted without the consideration of non-Newtonian rheology. In EHL numerical studies, the non-Newtonian properties and the constitutive equations are expressed by the concept of generalized viscosity [Formula: see text], which can be either a function of shear rate [Formula: see text] or a function of shear stress [Formula: see text]. In this way, a non-Newtonian lubrication problem could be solved as a generalized Newtonian problem based on solvers for a Newtonian EHL problem. According to the function of the generalized viscosity [Formula: see text], numerical solutions can be classified into shear rate-based ones and shear stress-based ones. In this work, these two kinds of numerical solutions are revisited. And their efficiency is compared for a two-dimensional (2D) non-Newtonian point contact EHL problem (here 2D means non-Newtonian flow in both the x and y directions). Results show that the shear rate-based numerical solution has a higher efficiency than the shear stress-based one. The shear rate-based 2D generalized Newtonian method is more suitable to analyze multiple EHL contacts in angular contact ball bearings and gears with complex 2D flow and/or transient EHL lubrication problems.

Sign in / Sign up

Export Citation Format

Share Document