Pulsatile Flow Through a Bifurcation With a Cerebrovascular Aneurysm

1994 ◽  
Vol 116 (1) ◽  
pp. 112-118 ◽  
Author(s):  
Tong-Miin Liou ◽  
Tzung-Wu Chang ◽  
Wen-Chin Chang
Keyword(s):  
Volume Flow Rate ◽  
Reynolds Numbers ◽  
Parent Vessel ◽  
Bifurcation Angle ◽  
Flow Through ◽  
The Mean ◽  
Rate Ratios ◽  
Flow Activity ◽  
Aneurysm Model ◽  
Made In

Laser-Doppler velocimetry measurements and flow visualization were complementarily made in pulsatile and steady flow in a cerebrovascular aneurysm model with bifurcation angles of 60, 90, and 140 deg, and volume-flow rate ratios between the branches of 1 to 1 and 3 to 1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. For uneven branch flow, it is found that the flow activity inside the aneurysm and the stresses acting on the aneurysmal wall increase with increasing bifurcation angle. More importantly, the present angle suggests the presence of a critical bifurcation angle below which the aneurysm is prone to thrombosis, whereas above which the aneurysm is susceptible to progression or rupture. For evenly distributed branch flow, the intra-aneurysmal flow is sluggish and therefore prone to thrombosis for all studied bifurcation angles.

Intra-Aneurysmal Flow With Helix and Mesh Stent Placement Across Side-Wall Aneurysm Pore of a Straight Parent Vessel

2004 ◽  
Vol 126 (1) ◽  
pp. 36-43 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shun-Nan Liou ◽  
Kai-Lung Chu
Keyword(s):  
Average Velocity ◽  
Side Wall ◽  
Reynolds Numbers ◽  
Shear Stresses ◽  
Parent Vessel ◽  
The Mean ◽  
Wall Shear ◽  
Comparison Of The Results ◽  
Flow Stasis ◽  
Aneurysm Model

Pulsatile flow fields in a cerebrovascular side-wall aneurysm model with a wide ostium after stenting are presented in terms of particle tracking velocimetry measurements and flow visualization. Among the stent parameters the shape, helix versus mesh, was selected to study its effect on the changes of intraaneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The blocking ratio of the stents was fixed at 30%. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. Four consecutive flow-rate phases were selected to characterize the intra-aneurysmal flow. The results are characterized in terms of velocity vector field, regional average velocity, and intra-aneurysmal vorticity/circulation/wall shear stress. It is found that the hemodynamic features inside the aneurysm alter markedly with the shape of the stent and the size of the orifice. Both stents investigated induce favorable changes in the intra-aneurysmal flow stasis as well as direction and undulation of wall shear stresses. A comparison of the results of the helix to mesh stent shows that the former is more favorable for endovascular treatment.

Modeling of Flow in a Straight Stented and Nonstented Side Wall Aneurysm Model

1997 ◽  
Vol 119 (2) ◽  
pp. 206-212 ◽  
Author(s):  
M. Aenis ◽  
A. P. Stancampiano ◽  
A. K. Wakhloo ◽  
B. B. Lieber
Keyword(s):  
Finite Element ◽  
Stent Placement ◽  
Fluid Dynamic ◽  
Side Wall ◽  
Flow Patterns ◽  
Parent Vessel ◽  
Similarity Parameter ◽  
Cross Sectional ◽  
Flow Activity ◽  
Aneurysm Model

We investigated the changes of flow patterns in a blood vessel with a side wall aneurysm resulting from placement of a stent. Local hemodynamics can be markedly altered by placing an intravascular stent, which covers the orifice of the aneurysm. The alterations in flow patterns can lead to flow stasis in the aneurysmal pouch and promote the formation of a stable thrombus. Furthermore, a porous stent can serve as substrate for neointimal growth and subsequently induce a remodeling of the diseased arterial segment. To examine changes in local hemodynamics due to stent placement, a stented and nonstented aneurysm model was investigated computationally in a three-dimensional configuration using a finite element fluid dynamics program. The finite element model was studied under incompressible, pulsatile, viscous, Newtonian conditions. The fluid dynamic similarity parameter, i.e., the maximum/minimum Reynolds number, was set at about 240/25 based on cross-sectional average instantaneous flow. The Womersley number was set to 2.5. These values are representative of large cerebral arteries. The results of the stented versus the nonstented model show substantial differences in flow patterns inside the aneurysmal pouch. Flow activity inside the stented aneurysm model is significantly diminished and flow inside the parent vessel is less undulated and is directed past the orifice. A high-pressure zone at the distal neck and the dome of the aneurysm prior to stenting decreases after stent placement. However, elevated pressure values are found at the stent filaments facing the current. Higher shear rates are observed at the distal aneurysmal neck after stenting, but are confined to a smaller region and are unidirectional compared to the nonstented model.

The dispersion of matter in turbulent flow through a pipe

1954 ◽  
Vol 223 (1155) ◽  
pp. 446-468 ◽  
Keyword(s):  
Turbulent Flow ◽  
Capillary Tube ◽  
Resistance Coefficient ◽  
Mean Flow ◽  
Combined Action ◽  
Flow Through ◽  
The Mean ◽  
Coefficient Of Diffusion ◽  
Good Agreement ◽  
Made In

The dispersion of soluble matter introduced into a slow stream of solvent in a capillary tube can be described by means of a virtual coefficient of diffusion (Taylor 1953 a ) which represents the combined action of variation of velocity over the cross-section of the tube and molecluar diffusion in a radial direction. The analogous problem of dispersion in turbulent flow can be solved in the same way. In that case the virtual coefficient of diffusion K is found to be 10∙1 av * or K = 7∙14 aU √ γ . Here a is the radius of the pipe, U is the mean flow velocity, γ is the resistance coefficient and v * ‘friction velocity’. Experiments are described in which brine was injected into a straight 3/8 in. pipe and the conductivity recorded at a point downstream. The theoretical prediction was verified with both smooth and very rough pipes. A small amount of curvature was found to increase the dispersion greatly. When a fluid is forced into a pipe already full of another fluid with which it can mix, the interface spreads through a length S as it passes down the pipe. When the interface has moved through a distance X , theory leads to the formula S 2 = 437 aX ( v * / U ). Good agreement is found when this prediction is compared with experiments made in long pipe lines in America.

Compressible Gas Flow Through Smooth and Rough Microchannels

2001 ◽  
Author(s):  
Stephen E. Turner ◽  
Otto J. Gregory
Keyword(s):  
Gas Flow ◽  
Rectangular Cross Section ◽  
Continuum Theory ◽  
Reynolds Numbers ◽  
Silicon Wafers ◽  
Constant Area ◽  
Flow Through ◽  
Compressible Gas Flow ◽  
Made In ◽  
Compressible Gas

Abstract This paper presents an experimental investigation on compressible gas flow through microchannels with a constant area, rectangular cross-section. The microchannels are etched into silicon wafers, capped with smooth glass, and have hydraulic diameters between 4 and 100 μm. All measurements were made in the laminar flow regime with Reynolds numbers ranging from 0.02 to 1000. Smooth channels were obtained by etching (100) silicon wafers with potassium hydroxide (KOH) solution. Rough channel surfaces were obtained by etching (110) silicon wafers with KOH. The investigation shows that the friction factor for both smooth and rough microchannels compares closely with continuum theory.

Moderate Reynolds number flows through periodic and random arrays of aligned cylinders

1997 ◽  
Vol 349 ◽  
pp. 31-66 ◽  
Author(s):  
DONALD L. KOCH ◽  
ANTHONY J. C. LADD
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Volume Fraction ◽  
Unit Length ◽  
Reynolds Numbers ◽  
Moderate Reynolds Number ◽  
Random Arrays ◽  
Flow Through ◽  
The Mean ◽  
Square Array

The effects of fluid inertia on the pressure drop required to drive fluid flow through periodic and random arrays of aligned cylinders is investigated. Numerical simulations using a lattice-Boltzmann formulation are performed for Reynolds numbers up to about 180.The magnitude of the drag per unit length on cylinders in a square array at moderate Reynolds number is strongly dependent on the orientation of the drag (or pressure gradient) with respect to the axes of the array; this contrasts with Stokes flow through a square array, which is characterized by an isotropic permeability. Transitions to time-oscillatory and chaotically varying flows are observed at critical Reynolds numbers that depend on the orientation of the pressure gradient and the volume fraction.In the limit Re[Lt ]1, the mean drag per unit length, F, in both periodic and random arrays, is given by F/(μU) =k1+k2Re2, where μ is the fluid viscosity, U is the mean velocity in the bed, and k1 and k2 are functions of the solid volume fraction ϕ. Theoretical analyses based on point-particle and lubrication approximations are used to determine these coefficients in the limits of small and large concentration, respectively.In random arrays, the drag makes a transition from a quadratic to a linear Re-dependence at Reynolds numbers of between 2 and 5. Thus, the empirical Ergun formula, F/(μU) =c1+c2Re, is applicable for Re>5. We determine the constants c1 and c2 over a wide range of ϕ. The relative importance of inertia becomes smaller as the volume fraction approaches close packing, because the largest contribution to the dissipation in this limit comes from the viscous lubrication flow in the small gaps between the cylinders.

The Distortion of Turbulent Velocity and Temperature Profiles on Heating, for Mercury in a Vertical Pipe

1974 ◽  
Vol 96 (2) ◽  
pp. 152-158 ◽  
Author(s):  
H. O. Buhr ◽  
E. A. Horsten ◽  
A. D. Carr
Keyword(s):  
Heat Input ◽  
Reynolds Numbers ◽  
High Heat ◽  
Vertical Pipe ◽  
Eddy Diffusivities ◽  
Limiting Profile ◽  
Buoyancy Forces ◽  
High Heat Input ◽  
The Mean ◽  
Made In

Measurements were made in mercury, for turbulent flow and constant flux heating in a vertical pipe, in order to determine the extent to which the velocity and temperature distributions are affected by buoyancy forces. With increasing heat flux, velocity profiles at Reynolds numbers of 20,000 to 60,000 were found to be markedly distorted in comparison with the isothermal velocity profile. Even very low heat input caused significant distortion, while at high heat input a limiting profile shape was approached, with the center velocity well below the mean and the maximum occurring in the vicinity of the wall. Eddy diffusivities of heat and momentum calculated from the measured profiles exhibit a considerable variation with heat input, indicating that buoyancy forces not only change the radial shear stress distribution but also alter the nature of the turbulence in the pipe.

Addressing Concentration Spaces by Multi Injectors for Micro Fluid Segment Sequences

2008 ◽  
Author(s):  
P. Mike Gu¨nther ◽  
Frances Mo¨ller ◽  
Thomas Henkel ◽  
J. Michael Ko¨hler
Keyword(s):  
Two Dimensional ◽  
Cell Cultivation ◽  
Glass Technology ◽  
Line Flow ◽  
Orange G ◽  
Flow Through ◽  
Rate Ratios ◽  
Concentration Space ◽  
Double Twin ◽  
Made In

Micro fluid segments attract increasing interest due to the possibility of easy generation, manipulation and use for diagnostics, chemical analytics, synthesis, cell cultivation and chemical as well as biological screenings. The addressing of chemical composition is a very important precondition for the application of micro fluid segments in highly parallelized operations. Here, we report the addressing of larger concentration spaces by use of a double-twin injector made in micro lithographic glass/glass technology. Two-dimensional concentration distributions can be achieved by varying flow rate ratios during the formation of fluid segments. Two different dyes (Orange G and Crystal violet) have been used to generate the two dimensional concentration space. The composition of dye containing segments is monitored by in-line flow-through micro photometry.

Stochastic homogenization and macroscopic modelling of composites and flow through porous media

2002 ◽  
pp. 337-378 ◽  
Author(s):  
Jozef Telega ◽  
Wlodzimierz Bielski
Keyword(s):  
Porous Medium ◽  
Random Distribution ◽  
Flow Through Porous Media ◽  
Macroscopic Models ◽  
Linear Elastic ◽  
Multi Scale ◽  
Convergence Method ◽  
Flow Through ◽  
The Mean ◽  
Random Porous Medium

The aim of this contribution is mainly twofold. First, the stochastic two-scale convergence in the mean developed by Bourgeat et al. [13] is used to derive the macroscopic models of: (i) diffusion in random porous medium, (ii) nonstationary flow of Stokesian fluid through random linear elastic porous medium. Second, the multi-scale convergence method developed by Allaire and Briane [7] for the case of several microperiodic scales is extended to random distribution of heterogeneities characterized by separated scales (stochastic reiterated homogenization). .

Study of pumping effect in flow-through electrolysers

1983 ◽  
Vol 48 (8) ◽  
pp. 2232-2248 ◽  
Author(s):  
Ivo Roušar ◽  
Michal Provazník ◽  
Pavel Stuhl
Keyword(s):  
Natural Convection ◽  
Balance Equation ◽  
Volume Fraction ◽  
Industrial Applications ◽  
Pumping Effect ◽  
Flow Through ◽  
The Mean ◽  
The Difference

In electrolysers with recirculation, where a gas is evolved, the pumping of electrolyte from a lower to a higher level can be effected by natural convection due to the difference between the densities of the inlet electrolyte and the gaseous emulsion at the outlet. An accurate balance equation for calculation of the rate of flow of the pumped liquid is derived. An equation for the calculation of the mean volume fraction of bubbles in the space between the electrodes is proposed and verified experimentally on a pilot electrolyser. Two examples of industrial applications are presented.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

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