Flow Through a Realistic Arterial Geometry With Two Aneurysms: Mixing Characteristics and Residence Times

Abstract In the present work, we are presenting computational simulation results for the flow in a human right internal carotid artery, exhibiting two saccular aneurysms close to each other. We utilize computer tomography data in order to extract a realistic geometric description of the region of interest. Aspects of the flow inside the aneurysms are discussed in connection to secondary motion patterns and inflow-outflow regimes. We construct residence time maps that exhibit strong non-uniformity, connected to the existence of fluid entering only the first, only the second, or both aneurysms. Preliminary evidence that the inflow-outflow patterns of the two aneurysms may be leading to particularly complex flow and to chaotic mixing is discussed, based on the apparent properties of both the residence time map iso-contours and the basins of attraction of the two aneurysms. Particular attention is paid in establishing grid independence for the computed results and for this reason a second order spatial discretization scheme is utilized, with resolutions ranging from approximately 110,000 to 1,070,000 tetrahedra.

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Computational and Experimental Study of Enhanced Laminar Flow Heat Transfer in Three-Dimensional Sinusoidal Wavy-Plate-Fin Channels

Heat Transfer: Volume 1 ◽

10.1115/ht2003-47148 ◽

2003 ◽

Cited By ~ 8

Author(s):

Jiehai Zhang ◽

Arun Muley ◽

Joseph B. Borghese ◽

Raj M. Manglik

Keyword(s):

Heat Transfer ◽

Flow Behavior ◽

Computational Simulation ◽

Three Dimensional ◽

Heat Fluxes ◽

Staggered Grid ◽

Uniform Heat Flux ◽

Complex Flow ◽

Constant Property ◽

Fin Efficiency

Enhanced heat transfer characteristics of low Reynolds number airflows in three-dimensional sinusoidal wavy plate-fin channels are investigated. For the computational simulation, steady state, constant property, periodically developed, laminar forced convection is considered with the channel surface at the uniform heat flux condition; the wavy-fin is modeled by its two asymptotic limits of 100% and zero fin efficiency. The governing equations are solved numerically using finite-volume techniques for a non-orthogonal, non-staggered grid. Computational results for velocity and temperature distribution, isothermal Fanning friction factor f and Colburn factor j are presented for airflow rates in the range of 10 ≤ Re ≤ 1500. The numerical results are further compared with experimental data, with excellent agreement, for two different wavy-fin geometries. The influence of fin density on the flow behavior and the enhanced convection heat transfer are highlighted. Depending on the flow rate, a complex flow structure is observed, which is characterized by the generation, spatial growth and dissipation of vortices in the trough region of the wavy channel. The thermal boundary layers on the fin surface are periodically disrupted, resulting in high local heat fluxes. The overall heat transfer performance is improved considerably, compared to the straight channel with the same cross-section, with a relatively smaller increase in the associated pressure drop penalty.

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On LES Methods Applied to Seal Geometries

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-68840 ◽

2012 ◽

Cited By ~ 2

Author(s):

James Tyacke ◽

Richard Jefferson-Loveday ◽

Paul Tucker

Keyword(s):

Maximum Error ◽

Labyrinth Seal ◽

Navier Stokes ◽

Final Solution ◽

Complex Flow ◽

Eddy Simulation ◽

Wide Range ◽

Large Eddy ◽

Rans Models ◽

Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

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Steady Laminar Flow through Twisted Pipes: Fluid Flow in Square Tubes

Journal of Heat Transfer ◽

10.1115/1.3244542 ◽

1981 ◽

Vol 103 (4) ◽

pp. 785-790 ◽

Cited By ~ 19

Author(s):

J. H. Masliyah ◽

K. Nandakumar

Keyword(s):

Laminar Flow ◽

Reynolds Numbers ◽

Navier Stokes ◽

Navier Stokes Equation ◽

Dissipation Term ◽

Axial Velocity Profile ◽

Secondary Motion ◽

Qualitative Nature ◽

Flow Through ◽

Steady Laminar

The Navier-Stokes equation in a rotating frame of reference is solved numerically to obtain the flow field for a steady, fully developed laminar flow of a Newtonian fluid in a twisted tube having a square cross-section. The macroscopic force and energy balance equations and the viscous dissipation term are presented in terms of variables in a rotating reference frame. The computed values of friction factor are presented for dimensionless twist ratios, (i.e., length of tube over a rotation of π radians normalized with respect to half the width of tube) of 20, 10, 5 and 2.5 and for Reynolds numbers up to 2000. The qualitative nature of the axial velocity profile was observed to be unaffected by the swirling motion. The secondary motion was found to be most important near the wall.

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Determination of the Near-Wellbore Pressure Drop for Dual Casing in Hydraulic Fracturing and Refracturing Applications

10.2118/205234-ms ◽

2022 ◽

Author(s):

Joern Loehken ◽

Davood Yosefnejad ◽

Liam McNelis ◽

Bernd Fricke

Keyword(s):

Pressure Drop ◽

Hydraulic Fracturing ◽

Complex Flow ◽

Cement Layer ◽

Natural Rock ◽

Wellbore Pressure ◽

Flow Through ◽

The Difference ◽

Coefficient Of Discharge

Abstract Due to the increases in completion costs demand for production improvements, fracturing through double casing in upper reservoirs for mature wells and refracturing early stimulated wells to change the completion design, has become more and more popular. One of the most common technologies used to re-stimulate previously fracked wells, is to run a second, smaller casing or tubular inside of the existing and already perforated pipes of the completed well. The new inner and old outer casing are isolated from each other by a cement layer, which prevents any hydraulic communication between the pre-existing and new perforations, as well as between adjacent new perforations. For these smaller inner casing diameters, specially tailored and designed re-fracturing perforation systems are deployed, which can shoot casing entrance holes of very similar size through both casings, nearly independent of the phasing and still capable of creating tunnels reaching beyond the cement layer into the natural rock formation. Although discussing on the API RP-19B section VII test format has recently been initiated and many companies have started to test multiple casing scenarios and charge performance, not much is known about the complex flow through two radially aligned holes in dual casings. In the paper we will look in detail at the parameters which influence the flow, especially the Coefficient of Discharge of such a dual casing setup. We will evaluate how much the near wellbore pressure drop is affected by the hole's sizes in the first and second casing, respectively the difference between them and investigate how the cement layer is influenced by turbulences, which might build up in the annulus. The results will enhance the design and provide a better understanding of fracturing or refracturing through double casings for hydraulic fracturing specialists and both operation and services companies.

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A critical evaluation of a pilot scale subsurface flow wetland: 10 years after commissioning

Water Science & Technology ◽

10.2166/wst.1997.0231 ◽

1997 ◽

Vol 35 (5) ◽

pp. 337-343 ◽

Cited By ~ 4

Author(s):

Allan Batchelor ◽

Pierre Loots

Keyword(s):

Critical Evaluation ◽

Subsurface Flow ◽

Plug Flow ◽

Pilot Scale ◽

Preliminary Evidence ◽

Surface Flow ◽

Organic Load ◽

Hydraulic Load ◽

Flow Through ◽

Back Mixing

A pilot scale subsurface flow wetland, commissioned in 1986, has been continuously operated since 1990 at a hydraulic load of 330 mm/day and a corresponding organic load of 1200 kg/ha·day. At these loading rates preliminary evidence suggests that the microbial biomass in the wetland was dominated by anaerobes. Attempts to increase the hydraulic load resulted in surface flooding which was attributed to suspended solids clogging the surface. Despite short circuiting, revealed by tracer studies, COD removal exceeded 70%. The hydraulic flow through the wetland was modelled and was described as modified plug flow with a degree of back mixing. A comparative costing exercise revealed that the unit treatment cost of a combination of a subsurface flow wetland/nitrification column, surface flow wetland was lower than that of an activated sludge system treating the same volume of effluent.

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Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array

Energies ◽

10.3390/en13081977 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1977 ◽

Cited By ~ 5

Author(s):

Donald R. Noble ◽

Samuel Draycott ◽

Anup Nambiar ◽

Brian G. Sellar ◽

Jeffrey Steynor ◽

...

Keyword(s):

Numerical Models ◽

Ocean Energy ◽

Complex Flow ◽

Flow Measurements ◽

Power Extraction ◽

Tidal Turbines ◽

Tidal Stream ◽

Flow Through ◽

And Performance ◽

Structural Loading

Tidal stream turbines are subject to complex flow conditions, particularly when installed in staggered array configurations where the downstream turbines are affected by the wake and/or bypass flow of upstream turbines. This work presents, for the first time, methods for and results from the physical testing of three 1/15 scale instrumented turbines configured in a closely-spaced staggered array, and demonstrates experimentally that increased power extraction can be achieved through reduced array separation. A comprehensive set of flow measurements was taken during several weeks testing in the FloWave Ocean Energy Research Facility, with different configurations of turbines installed in the tank in a current of 0.8 m/s, to understand the effect that the front turbines have on flow through the array and on the inflow to the centrally placed rearmost turbine. Loads on the turbine structure, rotor, and blade roots were measured along with the rotational speed of the rotor to assess concurrently in real-time the effects of flow and array geometry on structural loading and performance. Operating in this closely-spaced array was found to improve the power delivered by the rear turbine by 5.7–10.4% with a corresponding increase in the thrust loading on the rotor of 4.8–7.3% around the peak power operating point. The experimental methods developed and results arising from this work will also be useful for further scale-testing elsewhere, validating numerical models, and for understanding the performance and loading of full-scale tidal stream turbines in arrays.

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Blood Damage Through a Bileaflet Mechanical Heart Valve: A Quantitative Computational Study Using a Multiscale Suspension Flow Solver

Journal of Biomechanical Engineering ◽

10.1115/1.4028105 ◽

2014 ◽

Vol 136 (10) ◽

Cited By ~ 16

Author(s):

B. Min Yun ◽

Cyrus K. Aidun ◽

Ajit P. Yoganathan

Keyword(s):

Numerical Method ◽

Heart Valves ◽

Computational Study ◽

Mechanical Heart Valve ◽

Complex Flow ◽

Damage Potential ◽

Spatiotemporal Resolution ◽

Jude Medical ◽

Blood Damage ◽

Flow Through

Bileaflet mechanical heart valves (BMHVs) are among the most popular prostheses to replace defective native valves. However, complex flow phenomena caused by the prosthesis are thought to induce serious thromboembolic complications. This study aims at employing a novel multiscale numerical method that models realistic sized suspended platelets for assessing blood damage potential in flow through BMHVs. A previously validated lattice-Boltzmann method (LBM) is used to simulate pulsatile flow through a 23 mm St. Jude Medical (SJM) Regent™ valve in the aortic position at very high spatiotemporal resolution with the presence of thousands of suspended platelets. Platelet damage is modeled for both the systolic and diastolic phases of the cardiac cycle. No platelets exceed activation thresholds for any of the simulations. Platelet damage is determined to be particularly high for suspended elements trapped in recirculation zones, which suggests a shift of focus in blood damage studies away from instantaneous flow fields and toward high flow mixing regions. In the diastolic phase, leakage flow through the b-datum gap is shown to cause highest damage to platelets. This multiscale numerical method may be used as a generic solver for evaluating blood damage in other cardiovascular flows and devices.

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Numerical Simulations of Turbulent Flow Through a 90° Elbow

Volume 2: Computational Fluid Dynamics ◽

10.1115/ajkfluids2019-5498 ◽

2019 ◽

Author(s):

Ravon Venters ◽

Brian Helenbrook ◽

Goodarz Ahmadi

Keyword(s):

Turbulent Flow ◽

Cross Section ◽

Navier Stokes ◽

Mean Square ◽

Reynolds Stresses ◽

Streamline Curvature ◽

Secondary Motion ◽

Flow Through ◽

The Mean ◽

Flow Transitions

Abstract Turbulent flow in an elbow has been numerically investigated. The flow was modeled using two approaches; Reynolds Averaged Navier-Stokes (RANS) and Direct Numerical Simulation (DNS) methods. The DNS allows for all the scales of turbulence to be evaluated, providing a detailed depiction of the flow. The RANS simulation, which is typically used in industry, evaluates time-averaged components of the flow. The numerical results are accompanied by experimental data, which was used to validate the two methods. Profiles of the mean and root-mean-square (RMS) fluctuating components were compared at various points along the midplane of the elbow. Upstream of the elbow, the predicted mean and RMS velocities from the RANS and DNS simulations compared well with the experiment, differing slightly near the walls. However, downstream of the elbow, the RANS deviated from the experiment and DNS, showing a longer region of flow re-circulation. This caused the mean and RMS velocities to significantly differ. Examining the cross-section flow field, secondary motion was clearly present. Upstream secondary motion of the first kind was observed which is caused by anisotropy of the reynolds stresses in the turbulent flow. Downstream of the bend, the flow transitions to secondary motion of the second kind which is caused by streamline curvature. Qualitatively, the RANS and DNS showed similar results upstream of the bend, however downstream, the magnitude of the secondary motion differed significantly.

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Plaque Progression in a Human Coronary Artery is Associated With Low Wall Shear Stress and Extended Particle Residence Time

ASME 2010 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2010-19344 ◽

2010 ◽

Author(s):

Jin Suo ◽

Michael McDaniel ◽

Parham Eshtehardi ◽

Saurabh Dhawan ◽

Ravi Prasad Avati Nanjundappa ◽

...

Keyword(s):

Shear Stress ◽

Coronary Artery ◽

Wall Shear Stress ◽

Residence Time ◽

Vigorous Physical Activity ◽

Region Of Interest ◽

Reconstruction Technique ◽

Plaque Progression ◽

Human Coronary Artery ◽

Wall Shear

Intravascular ultrasound (IVUS) evaluation was performed in the coronary arteries of a 45-year-old patient with stable angina during vigorous physical activity. Concurrent angiography demonstrated a mild plaque in the proximal left anterior descending artery (LAD), with obvious lumen dilatation immediately distal to the plaque. Blood velocity was measured by a catheter Doppler transducer at proximal and distal segments of the left coronary artery, and the left main artery (LM) and LAD were reconstructed using a 3D-IVUS reconstruction technique based on biplanar angiography and IVUS images, enabling simulation of the flow field in the artery employing computational fluid dynamics (CFD). Wall shear stress (WSS) and particle path lines were determined from the CFD studies. The patient returned for a follow up evaluation after 6 months, and plaque progression during this period was evaluated from the IVUS data. Results showed that low WSS, less than 5 dynes/cm2, which occurs in the region immediately distal to the plaque, correlates with localized progression of the lesion over the 6 month interval. The path line tracking computations showed that particles near the vessel surface where plaque progression was observed resided near the artery wall longer than one complete cardiac cycle, whereas in other areas particles were flushed through the region of interest rapidly. These observations in a specific individual are consistent with the hypothesis that plaque progression is related to low WSS and relatively long residence time of atherogenic blood-borne substances.

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