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.

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.

The Ratio of the Wall Shear Stresses in Concentric Annuli

1968 ◽  
Vol 72 (688) ◽  
pp. 345-346 ◽  
Author(s):  
Alan Quarmby
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
Radius Ratio ◽  
Experimental Results ◽  
Bulk Velocity ◽  
Shear Stresses ◽  
Wall Shear

Summary Experimental results are presented of the measurement of the ratio of the wall shear stresses at the inner and outer surfaces of concentric annuli. Five radius ratios were investigated with Reynolds numbers in the range 2000-89 000 with air. The Reynolds number is defined as where ū is the bulk velocity. It is concluded that the ratio of the shear stresses is very different from the corresponding laminar flow value and is a function of both radius ratio and Reynolds number.

M. J. Hartmann Memorial Session Paper: Turbulence Characteristics in a Supersonic Cascade Wake Flow

1994 ◽  
Vol 116 (4) ◽  
pp. 586-596 ◽  
Author(s):  
P. L. Andrew ◽  
Wing-fai Ng
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Shear Stresses ◽  
State University ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean ◽  
Supersonic Wake

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two-component laser-doppler anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near-wake and the far-wake. The extremities of profiles of both the mean and turbulent wake properties´ were found to be strongly influenced by upstream shock-boundary -layer interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23 percent, and the generally accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock-boundary-layer interactions has been superimposed.

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.

Shear Induced Removal of Calcium Carbonate Scale From Polypropylene and Copper Tubes

2009 ◽  
Author(s):  
Matt Royer ◽  
Jane H. Davidson ◽  
Lorraine F. Francis ◽  
Susan C. Mantell
Keyword(s):  
Shear Stress ◽  
Calcium Carbonate ◽  
Wall Shear Stress ◽  
Polymeric Materials ◽  
Reynolds Numbers ◽  
Shear Stresses ◽  
Solar Absorbers ◽  
Flow Through ◽  
Wall Shear ◽  
Calcium Carbonate Scale

This paper presents an analytical model and experimental study of adhesion and fluid shear removal of calcium carbonate scale on polypropylene and copper tubes in laminar and turbulent water flows, with a view toward understanding how scale can be controlled in solar absorbers and heat exchangers. The tubes are first coated with scale and then inserted in a flow through apparatus. Removal is measured gravimetrically for Reynolds numbers from 525 to 5550, corresponding to wall shear stresses from 0.16 to 6.0 Pa. The evolutionary structure of the scale is visualized with scanning electron microscopy. Consistent with the predictive model, calcium carbonate is more easily removed from polypropylene than copper. In a laminar flow with a wall shear stress of 0.16 Pa, 65% of the scale is removed from polypropylene while only 10% is removed from copper. Appreciable removal of scale from copper requires higher shear stresses. At Reynolds number of 5500, corresponding to a wall shear stress of 6.0 Pa, 30% of the scale is removed from the copper tubes. The results indicate scale will be more easily removed from polypropylene, and by inference other polymeric materials, than copper by flushing with water.

Nonasymptotic behavior of developing turbulent pipe flow

1976 ◽  
Vol 54 (3) ◽  
pp. 268-278 ◽  
Author(s):  
J. K. Reichert ◽  
R. S. Azad
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Reynolds Numbers ◽  
Peak Position ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Inlet Region ◽  
The Mean ◽  
Hot Film

Detailed measurements of mean velocity U profiles, in the inlet 70 diameters of a pipe, show that the development of turbulent pipe flow is nonasymptotic. Experiments were done at seven Reynolds numbers in the range 56 000–15 3000. Contours of U and V fields are presented for two representative Reynolds numbers. A U component peak exceeding the fully developed values has been found to occur along the pipe centerline. The Reynolds number behavior of the peak position has been determined. Hot film measurements of the mean wall shear stresses in the inlet region also show a nonasymptotic development consistent with the mean velocity results.

Near-Wall Measurements in Turbulent Boundary Layers Using Laser Doppler Anemometry

2002 ◽  
Author(s):  
T. Gunnar Johansson ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
The Mean ◽  
Wall Shear ◽  
Near Wall

Near wall measurements have been performed in a zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers using Laser-Doppler Anemometry in order to investigate how accurately the wall shear stress can be determined. Also, scaling problems are particularly difficult at low Reynolds numbers since they involve simultaneous influences of both inner and outer scales and this is most clearly observed in the near-wall region. In order to fully describe the zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers it is necessary to accurately measure a number of quantities. These include the mean velocity and Reynolds stresses, and their spatial derivatives all the way down to the wall (y+∼1). Integral parameters that need to be measured are the wall shear stress and boundary layer thickness, particularly the momentum thickness. Problems with the measurement of field properties get worse close to a wall, and they get worse for increasing local Reynolds number. Three different approaches to measure the wall shear stress were examined. It was found that small measurement errors in the mean velocity close to the wall significantly reduced the accuracy in determining the wall shear stress by measuring the velocity gradient at the wall. The constant stress layer was found to be affected by the advection terms. However, it was found that taking the small pressure gradient into account and improving on the spatial resolution in the outer part of the boundary layer made the momentum integral method reliable.

scholarly journals Impact of Stent Design on Intra-Aneurysmal Flow

2004 ◽  
Vol 10 (2_suppl) ◽  
pp. 85-94 ◽  
Author(s):  
M. Ohta ◽  
M. Hirabayashi ◽  
S. Wetzel ◽  
P. Lylyk ◽  
H. Wata ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Side Wall ◽  
Vortical Flow ◽  
Parent Artery ◽  
Parent Vessel ◽  
Navier Stokes Equation ◽  
Aneurysm Neck ◽  
Neck Area ◽  
The Mean ◽  
Vessel Axis

In addition to providing a skeleton for vessel reconstruction, stent implantation as used for cerebral aneurysm treatment can induce flow redirection, thus reducing vortical flow velocities within the aneurysm cavity. Further, stent characteristics such as strut size, porosity and cell shape influence the changes in intra-aneurysmal flow by analog simulations. The purpose of this computer simulation study was to visualize the flow pattern over the entire neck area of a side wall aneurysm while changing the stent parameters. A 3-D computer model aneurysm was constructed to have a parent artery of 5 mm diameter and an aneurysm of 10 mm diameter. The distance between the midline of main artery and center point of the aneurysm was 6.8 mm, providing a neck length of 5 mm, a width of 3.6 mm, and a neck area of 14 mm 2. The simulations were carried out with a Finite Element Method based flow simulation package. The incompressible Navier -Stokes equation was solved for a steady flow with a mean speed of 290 mm/s, steady viscosity of 3.83 cp, and density of 1.0 g/cm3. Two parallel stent struts (dimensions: 100 μm m 100 μm m 2.0 mm) were introduced into the plane of the aneurysm neck. The fraction of the aneurysm neck cross-section occupied by the stent was 2.83% in all cases. The velocity distribution through the neck of the aneurysm was calculated for three different choices of separation between the struts for each of two orientations of the struts (parallel and perpendicular) relative to the vessel axis. The flow pattern in the aneurysm was composed of an inflow zone at the distal neck and of an outflow zone at the proximal neck. The placement of stent struts at the aneurysm neck resulted in a decrease in the mean speed in the aneurysm. The degree of reduction and the distribution of flow through the neck did depend on the orientation of the stent struts. The struts, when placed parallel or perpendicular to the parent vessel axis affected the mean speed through the aneurysm neck differently.

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