Pulsatile Albumin Transport in Large Arteries: A Numerical Simulation Study

1996 ◽  
Vol 118 (4) ◽  
pp. 511-519 ◽  
Author(s):  
G. Rappitsch ◽  
K. Perktold
Keyword(s):  
Pulsatile Flow ◽  
Stokes Equations ◽  
Separated Flow ◽  
Flow Region ◽  
Navier Stokes ◽  
Permeability Model ◽  
Navier Stokes Equations ◽  
Area Reduction ◽  
Stenosed Artery ◽  
Percent Area

Albumin transport in a stenosed artery configuration is analyzed numerically under steady and pulsatile flow conditions. The flow dynamics is described applying the incompressible Navier-Stokes equations for Newtonian fluids, the mass transport is modelled using the convection diffusion equation. The boundary conditions describing the solute wall flux take into account the concept of endothelial resistance to albumin flux by means of a shear dependent permeability model based on experimental data. The study concentrates on the influence of steady and pulsatile flow patterns and of regional variations in vascular geometry on the solute wall flux and on the ratio of endothelial resistance to concentration boundary layer resistance. The numerical solution of the Navier-Stokes equations and of the transport equation applies the finite element method where stability of the convection dominated transport process is achieved by using an upwind procedure and a special subelement technique. Numerical simulations are carried out for albumin transport in a stenosed artery segment with 75 percent area reduction representing a late stage in the progression of an atherosclerotic disease. It is shown that albumin wall flux varies significantly along the arterial section, is strongly dependent upon the different flow regimes and varies considerably during a cardiac cycle. The comparison of steady results and pulsatile results shows differences up to 30 percent between time-averaged flux and steady flux in the separated flow region downstream the stenosis.

scholarly journals Numerical simulation of pulsatile blood flow: a study with normal artery, and arteries with single and multiple stenosis

2021 ◽  
Vol 68 (1) ◽  
Author(s):  
Md. Alamgir Kabir ◽  
Md. Ferdous Alam ◽  
Md. Ashraf Uddin
Keyword(s):  
Blood Flow ◽  
Numerical Simulations ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Area Reduction ◽  
Significant Difference ◽  
Stenosed Artery ◽  
Fluid Properties ◽  
Flow Through

AbstractNumerical simulations of pulsatile transitional blood flow through symmetric stenosed arteries with different area reductions were performed to investigate the behavior of the blood. Simulations were carried out through Reynolds averaged Navier-Stokes equations and well-known k-ω model was used to evaluate the numerical simulations to assess the changes in velocity distribution, pressure drop, and wall shear stress in the stenosed artery, artery with single and double stenosis at different area reduction. This study found a significant difference in stated fluid properties among the three types of arteries. The fluid properties showed a peak in an occurrence at the stenosis for both in the artery with single and double stenosis. The magnitudes of stated fluid properties increase with the increase of the area reduction. Findings may enable risk assessment of patients with cardiovascular diseases and can play a significant role to find a solution to such types of diseases.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

Self-Excited Oscillation of Transonic Flow Around an Airfoil in Two-Dimensional Channel

1989 ◽  
Author(s):  
Kazuomi Yamamoto ◽  
Yoshimichi Tanida
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Transonic Flow ◽  
Stokes Equations ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Layer Separation ◽  
Excited Oscillation

A self-excited oscillation of transonic flow in a simplified cascade model was investigated experimentally, theoretically and numerically. The measurements of the shock wave and wake motions, and unsteady static pressure field predict a closed loop mechanism, in which the pressure disturbance, that is generated by the oscillation of boundary layer separation, propagates upstream in the main flow and forces the shock wave to oscillate, and then the shock oscillation disturbs the boundary layer separation again. A one-dimensional analysis confirms that the self-excited oscillation occurs in the proposed mechanism. Finally, a numerical simulation of the Navier-Stokes equations reveals the unsteady flow structure of the reversed flow region around the trailing edge, which induces the large flow separation to bring about the anti-phase oscillation.

Numerical Investigation of Blade Flutter at or Near Stall in Axial Flow Turbomachines

2001 ◽  
Author(s):  
Wolfgang Höhn
Keyword(s):  
Viscous Flow ◽  
Stokes Equations ◽  
Separated Flow ◽  
Parallel Computer ◽  
Navier Stokes ◽  
Computational Domain ◽  
Compressor Cascade ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Blade Flutter

During the design of the compressor and turbine stages of today’s aeroengines, aerodynamically induced vibrations become increasingly important since higher blade load and better efficiency are desired. In this paper the development of a method based on the unsteady, compressible Navier-Stokes equations in two dimensions is described in order to study the physics of flutter for unsteady viscous flow around cascaded vibrating blades at stall. The governing equations are solved by a finite difference technique in boundary fitted coordinates. The numerical scheme uses the Advection Upstream Splitting Method to discretize the convective terms and central differences discretizing the viscous terms of the fully non-linear Navier-Stokes equations on a moving H-type mesh. The unsteady governing equations are explicitly and implicitly marched in time in a time-accurate way using a four stage Runge-Kutta scheme on a parallel computer or an implicit scheme of the Beam-Warming type on a single processor. Turbulence is modelled using the Baldwin-Lomax turbulence model. The blade flutter phenomenon is simulated by imposing a harmonic motion on the blade, which consists of harmonic body translation in two directions and a rotation, allowing an interblade phase angle between neighboring blades. Non-reflecting boundary conditions are used for the unsteady analysis at inlet and outlet of the computational domain. The computations are performed on multiple blade passages in order to account for nonlinear effects. A subsonic massively stalled unsteady flow case in a compressor cascade is studied. The results, compared with experiments and the predictions of other researchers, show reasonable agreement for inviscid and viscous flow cases for the investigated flow situations with respect to the Steady and unsteady pressure distribution on the blade in separated flow areas as well as the aeroelastic damping. The results show the applicability of the scheme for stalled flow around cascaded blades. As expected the viscous and inviscid computations show different results in regions where viscous effects are important, i.e. in separated flow areas. In particular, different predictions for inviscid and viscous flow for the aerodynamic damping for the investigated flow cases are found.

Modeling of Particulate Pressure in the Frame of Mesoscopic Eulerian Formalism for Compressible Reactive Dispersed Two-Phase Flows

2006 ◽  
Author(s):  
M. Simoes ◽  
O. Simonin
Keyword(s):  
Stokes Equations ◽  
Flow Region ◽  
Navier Stokes ◽  
Two Phase Flows ◽  
Two Phase ◽  
Specific Flow ◽  
Navier Stokes Equations ◽  
Rocket Motors ◽  
Eulerian Approach ◽  
Liquid Rocket

In space propulsion, compressible reactive dispersed two-phase flows are investigated in order to predict the behavior of solid or liquid rocket motors. In the frame of full Eulerian approach, physical modeling of aerodynamic flows in such motors is performed resolving unsteady compressible Navier-Stokes equations for both phases. However, numerical simulations performed on a simple axisymmetric motor have pointed out a flaw of this basic Eulerian approach. Indeed, the variance of the particle velocity distribution is not accounted for, leading to unrealistic accumulations of particles in some specific flow region. To correct this shortcoming, we have developed an advanced Eulerian model based on a statistical approach in the framework of the Mesoscopic Eulerian Formalism (MEF).

The Effect of Constriction Size on the Pulsatile Flow in a Channel

1995 ◽  
Vol 117 (4) ◽  
pp. 571-576 ◽  
Author(s):  
Moshe Rosenfeld ◽  
Shmuel Einav
Keyword(s):  
Pulsatile Flow ◽  
Stokes Equations ◽  
Thrombus Formation ◽  
Propagation Speed ◽  
Navier Stokes ◽  
Flow Structures ◽  
Incoming Flow ◽  
Noninvasive Methods ◽  
Navier Stokes Equations ◽  
Potential Damage

The effect of the constriction size on the pulsatile flow in a channel is studied by solving the time-dependent incompressible Navier-Stokes equations. A pulsating incoming flow is specified at the upstream boundary and the flow is investigated for several constriction sizes. Large flow structures are developed downstream of the constriction even for very small constriction size. The flow structures consist of several vortices that are created in each cycle and propagate downstream until they are washed away with the acceleration of the incoming flow. Additional vortices are created by a vortex multiplication process. The strength and total number of vortices generated in each cycle increase with the severity of the constriction. The maximal size of the vortices as well as their propagation speed are independent of the constriction size. These findings may be used for devising noninvasive methods for detecting the severity of stenoses in blood vessels and the potential damage to blood elements and thrombus formation caused by vortices.

Stokes flow between two intersecting circular arcs

1965 ◽  
Vol 61 (1) ◽  
pp. 271-274 ◽  
Author(s):  
K. B Ranger
Keyword(s):  
Reynolds Number ◽  
Stokes Flow ◽  
Stokes Equations ◽  
Flow Region ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Reynolds Number Flow ◽  
Circular Arcs ◽  
Converging Flow ◽  
Point Of Intersection

This paper considers a family of viscous flows closely related to the exact Jeffery-Hamel solution ((l), (2)) of the two-dimensional Navier-Stokes equations, for diverging or converging flow in a channel. It is known that if the walls of the channel intersect at an angle less than π then there is a unique solution of the Navier-Stokes equations in which the streamlines are straight lines issuing from the point of intersection of the walls and the flow is everywhere diverging or everywhere converging. The flow parameters depend on the total fluid mass M emitted at the point of intersection and the angle 2α between the walls. By taking the Reynolds number R = M/ν, where v is the kinematic viscosity, the stream function can be expanded in a power series in R in which the leading term is a Stokes flow. Alternatively the solution can be developed by perturbing the Stokes flow and is one of very few examples known in which a Stokes flow can be regarded as a uniformly valid first approximation everywhere in an infinite fluid region. The class of flows to be considered is a generalization of the Jeffery–Hamel flow by taking the flow region to be finite and bounded by two circular arcs which intersect at an angle less than π At one point of intersection fluid is forced into the region and an equal amount is absorbed out at the other point. It is found to the first order that the flow at the two points of intersection corresponds to the zero Reynolds number limit for diverging and converging flow, respectively. Now since the flow at these points can be developed by perturbing the Stokes flow solution it is reasonable to assume that the zero Reynolds number flow in the entire finite region bounded by the arcs is a Stokes flow since the most likely region in which this approximation becomes invalid is locally at the points of intersection but here the validity of the approximation is ensured. A comparison of the convection terms with the viscous terms verifies that this conclusion is borne out.

Geometrical Effects on Fluid Mixing of Pulsatile Flow in Convergent-Divergent Micromixer

2015 ◽  
Author(s):  
Arshad Afzal ◽  
Kwang-Yong Kim
Keyword(s):  
Pulsatile Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Geometrical Parameters ◽  
Navier Stokes Equations ◽  
Mixing Performance ◽  
Throat Width ◽  
Pulsatile Flows ◽  
Geometrical Effects ◽  
Diffusion Convection

Time-dependent pulsatile flows have been used by many researchers for fast and efficient mixing at micro-scale [1–2]. In a recent study, a convergent-divergent microchannel with sinusoidal walls showed a strong coupling with pulsatile flow for enhanced mixing performance over a short mixing length [3]. In the present study, effects of two geometrical parameters, i.e., the ratio of amplitude to wavelength and ratio of throat-width to depth on mixing performance, were analyzed with the Strouhal number and the ratio of pulsing amplitude to steady flow velocity at a fixed Reynolds number, Re = 0.5. The flow and mixing analyses were performed using unsteady Navier-Stokes equations and a diffusion-convection model for species concentration.

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