Radial Stagnation Flow on a Twisting Cylinder

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Patrick Weidman
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shooting Method ◽  
Azimuthal Velocity ◽  
Shear Stresses ◽  
Torsional Motion ◽  
Stagnation Flow ◽  
Strong Function ◽  
Stress Parameter ◽  
Wall Shear

The problem of stagnation-point flow impinging radially on a linearly twisting cylinder is considered. This advances previous work on the motion outside a cylinder undergoing linear torsional motion. The problem is governed by a Reynolds number R and a dimensionless torsion rate σ. Numerical calculations are carried out using the ODEINT program, and convergence of the shooting method is obtained using the MNEWT program. The radial and azimuthal wall shear stresses are found over a range of R and σ, and radial and azimuthal velocity profiles at σ={0,1,2} are presented for various values of R. The interesting feature is that the axial wall shear stress parameter f″(1) is a very weak function of σ while the azimuthal wall shear stress parameter g′(1) is a strong function of σ although both stress parameters are a strong function of R.

Preston-Static Tubes for the Measurement of Wall Shear Stress

1994 ◽  
Vol 116 (3) ◽  
pp. 645-649 ◽  
Author(s):  
Josef Daniel Ackerman ◽  
Louis Wong ◽  
C. Ross Ethier ◽  
D. Grant Allen ◽  
Jan K. Spelt
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Convenient Method ◽  
Pipe Flow ◽  
Total Pressure ◽  
Static Pressure ◽  
Shear Stresses ◽  
Streamline Curvature ◽  
Syringe Needle ◽  
Wall Shear

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Requirements for Mesh Resolution in 3D Computational Hemodynamics

2000 ◽  
Vol 123 (2) ◽  
pp. 134-144 ◽  
Author(s):  
Sujata Prakash ◽  
C. Ross Ethier
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Velocity Fields ◽  
Shear Stresses ◽  
Large Artery ◽  
Mesh Independence ◽  
Wall Shear

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features. Here we examine, for a single arterial geometry, how velocity and wall shear stress patterns depend on mesh characteristics. A well-validated Navier-Stokes solver was used to simulate flow in an anatomically realistic human right coronary artery (RCA) using unstructured high-order tetrahedral finite element meshes. Velocities, wall shear stresses (WSS), and wall shear stress gradients were computed on a conventional “high-resolution” mesh series (60,000 to 160,000 velocity nodes) generated with a commercial meshing package. Similar calculations were then performed in a series of meshes generated through an adaptive mesh refinement (AMR) methodology. Mesh-independent velocity fields were not very difficult to obtain for both the conventional and adaptive mesh series. However, wall shear stress fields, and, in particular, wall shear stress gradient fields, were much more difficult to accurately resolve. The conventional (nonadaptive) mesh series did not show a consistent trend towards mesh-independence of WSS results. For the adaptive series, it required approximately 190,000 velocity nodes to reach an r.m.s. error in normalized WSS of less than 10 percent. Achieving mesh-independence in computed WSS fields requires a surprisingly large number of nodes, and is best approached through a systematic solution-adaptive mesh refinement technique. Calculations of WSS, and particularly WSS gradients, show appreciable errors even on meshes that appear to produce mesh-independent velocity fields.

scholarly journals Assessing Bioinspired Topographies for their Antifouling Potential Control Using Computational Fluid Dynamics (CFD)

2018 ◽  
Vol 152 ◽  
pp. 02004 ◽  
Author(s):  
Jacky Ling ◽  
Felicia Wong Yen Myan
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Extended Period ◽  
Slip Boundary Condition ◽  
Shear Stresses ◽  
Cfd Simulations ◽  
Potential Control ◽  
Slip Boundary ◽  
Computational Fluid Dynamics Cfd ◽  
Wall Shear

Biofouling is the accumulation of unwanted material on surfaces submerged or semi submerged over an extended period. This study investigates the antifouling performance of a new bioinspired topography design. A shark riblets inspired topography was designed with Solidworks and CFD simulations were antifouling performance. The study focuses on the fluid flow velocity, the wall shear stress and the appearance of vortices are to be noted to determine the possible locations biofouling would most probably occur. The inlet mass flow rate is 0.01 kgs-1 and a no-slip boundary condition was applied to the walls of the fluid domain. Simulations indicate that Velocity around the topography averaged at 7.213 x 10-3 ms-1. However, vortices were observed between the gaps. High wall shear stress is observed at the peak of each topography. In contrast, wall shear stress is significantly low at the bed of the topography. This suggests the potential location for the accumulation of biofouling. Results show that bioinspired antifouling topography can be improved by reducing the frequency of gaps between features. Linear surfaces on the topography should also be minimized. This increases the avenues of flow for the fluid, thus potentially increasing shear stresses with surrounding fluid leading to better antifouling performance.

scholarly journals Numerical Simulation of Dispersed Particle-Blood Flow in the Stenosed Coronary Arteries

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Mongkol Kaewbumrung ◽  
Somsak Orankitjaroen ◽  
Pichit Boonkrong ◽  
Buraskorn Nuntadilok ◽  
Benchawan Wiwatanapataphee
Keyword(s):  
Numerical Simulation ◽  
Blood Flow ◽  
Shear Stress ◽  
Coronary Artery ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Stokes Equations ◽  
Spherical Shape ◽  
Shear Stresses ◽  
Wall Shear

A mathematical model of dispersed bioparticle-blood flow through the stenosed coronary artery under the pulsatile boundary conditions is proposed. Blood is assumed to be an incompressible non-Newtonian fluid and its flow is considered as turbulence described by the Reynolds-averaged Navier-Stokes equations. Bioparticles are assumed to be spherical shape with the same density as blood, and their translation and rotational motions are governed by Newtonian equations. Impact of particle movement on the blood velocity, the pressure distribution, and the wall shear stress distribution in three different severity degrees of stenosis including 25%, 50%, and 75% are investigated through the numerical simulation using ANSYS 18.2. Increasing degree of stenosis severity results in higher values of the pressure drop and wall shear stresses. The higher level of bioparticle motion directly varies with the pressure drop and wall shear stress. The area of coronary artery with higher density of bioparticles also presents the higher wall shear stress.

Analysis of Flow Disturbance in a Stenosed Carotid Artery Bifurcation Using Two-Equation Transitional and Turbulence Models

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
F. P. P. Tan ◽  
G. Soloperto ◽  
S. Bashford ◽  
N. B. Wood ◽  
S. Thom ◽  
...  
Keyword(s):  
Shear Stress ◽  
Carotid Artery ◽  
Laminar Flow ◽  
Wall Shear Stress ◽  
Turbulence Models ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Shear Stresses ◽  
Zone Length ◽  
Wall Shear

In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter’s hybrid k‐ϵ∕k‐ω shear stress transport (SST) model and its “scale adaptive simulation” (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant.

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.

Compaction and flow of potato starch and potato granules Compactación y flujo de almidón de patata y gránulos de patata

1997 ◽  
Vol 3 (5) ◽  
pp. 333-342 ◽  
Author(s):  
P.J. Halliday ◽  
A.C. Smith
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Water Content ◽  
Capillary Flow ◽  
Potato Starch ◽  
Slip Flow ◽  
Shear Stresses ◽  
Wall Shear ◽  
Water Contents

Potato starch and potato granules are materials that are often used in extrusion processes. It is important to quantify their rheology for modelling and prediction of process performance. The compaction behaviour of potato starch was examined at water contents of 4-18% wwb (wet weight basis) for pressures between 1 and 85 MPa. The Heckel deformation stress decreased as the water content increased up to 12% but became inaccurate at 18%. This decrease agreed qualitatively with other observations of the decrease in stiffness of starchy materials over this water content range. Potato granules were examined at water contents of 25-45% wwb and aspects of their rheo logical behaviour characterized using different approaches. A first approximation used the shear viscosity-shear rate power law which produced a law exponent for the resulting pastes (0.1-0.2). The classical Benbow equation was used to estimate yield and wall shear stresses in capillary flow. The latter indicates the presence of slip which was examined more fully as a function of wall shear stress. The Mooney technique was used together with a variation of the method where the shear rate for each die was subtracted from that for a non-slip flow, which was approximated using rough dies. A critical wall shear stress for slip was found to be 0.05-0.1 MPa, making it consistent with published results for other materials.

Blood Flow Manipulation in the Aorta With Coarctation and Arch Narrowing for Pediatric Subjects

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Yuxi Jia ◽  
Kumaradevan Punithakumar ◽  
Michelle Noga ◽  
Arman Hemmati
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Arch ◽  
Flow Direction ◽  
Upper Body ◽  
Patient Specific ◽  
Shear Stresses ◽  
Wall Shear

Abstract The characteristics of blood flow in an abnormal pediatric aorta with an aortic coarctation and aortic arch narrowing are examined using direct numerical simulations and patient-specific boundary conditions. The blood flow simulations of a normal pediatric aorta are used for comparison to identify unique flow features resulting from the aorta geometrical anomalies. Despite flow similarities compared to the flow in normal aortic arch, the flow velocity decreases with an increase in pressure, wall shear stress, and vorticity around both anomalies. The presence of wall shear stresses in the trailing indentation region and aorta coarctation opposing the primary flow direction suggests that there exist recirculation zones in the aorta. The discrepancy in relative flowrates through the top and bottom of the aorta outlets, and the pressure drop across the coarctation, implies a high blood pressure in the upper body and a low blood pressure in the lower body. We propose using flow manipulators prior to the aortic arch and coarctation to lower the wall shear stress, while making the recirculation regions both smaller and weaker. The flow manipulators form a guide to divert and correct blood flow in critical regions of the aorta with anomalies.

Induction of NO and prostaglandin E2 in osteoblasts by wall-shear stress but not mechanical strain

1997 ◽  
Vol 273 (4) ◽  
pp. E751-E758 ◽  
Author(s):  
R. Smalt ◽  
F. T. Mitchell ◽  
R. L. Howard ◽  
T. J. Chambers
Keyword(s):  
Shear Stress ◽  
Fluid Flow ◽  
Wall Shear Stress ◽  
Bone Cells ◽  
Mechanical Strain ◽  
Osteoblastic Cells ◽  
Long Bone ◽  
Shear Stresses ◽  
No Production ◽  
Wall Shear

The nature of the stimulus sensed by bone cells during mechanical usage has not yet been determined. Because nitric oxide (NO) and prostaglandin (PG) production appear to be essential early responses to mechanical stimulation in vivo, we used their production to compare the responsiveness of bone cells to strain and fluid flow in vitro. Cells were incubated on polystyrene film and subjected to unidirectional linear strains in the range 500–5,000 microstrain (με). We found no increase in NO or PGE2 production after loading of rat calvarial or long bone cells, MC3T3-E1, UMR-106–01, or ROS 17/2.8 cells. In contrast, exposure of osteoblastic cells to increased fluid flow induced both PGE2 and NO production. Production was rapidly induced by wall-shear stresses of 148 dyn/cm2 and was observed in all the osteoblastic populations used but not in rat skin fibroblasts. Fluid flow appeared to act through an increase in wall-shear stress. These data suggest that mechanical loading of bone is sensed by osteoblastic cells through fluid flow-mediated wall-shear stress rather than by mechanical strain.

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