Inlet Conditions for Image-Based CFD Models of the Carotid Bifurcation: Is it Reasonable to Assume Fully Developed Flow?

2006 ◽  
Vol 128 (3) ◽  
pp. 371-379 ◽  
Author(s):  
Keri R. Moyle ◽  
Luca Antiga ◽  
David A. Steinman
Keyword(s):  
Secondary Flow ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Fully Developed Flow ◽  
Bifurcation Method ◽  
Inlet Velocity ◽  
Cfd Models ◽  
Measurement Tools ◽  
Inlet Conditions ◽  
Geometry Simplification

Background: Computational fluid dynamics tools are useful for their ability to model patient specific data relevant to the genesis and progression of atherosclerosis, but unavailable to measurement tools. The sensitivity of the physiologically relevant parameters of wall shear stress (WSS) and the oscillatory shear index (OSI) to secondary flow in the inlet velocity profiles was investigated in three realistic models of the carotid bifurcation. Method of Approach: Secondary flow profiles were generated using sufficiently long entrance lengths, to which curvature and helical pitch were added. The differences observed were contextualized with respect to effect of the uncertainty of the models’ geometry on the same parameters. Results: The effects of secondary velocities in the inlet profile on WSS and OSI break down within a few diameters of the inlet. Overall, the effect of secondary inlet flow on these models was on average more than 3.5 times smaller than the effect of geometric variability, with 13% and 48% WSS variability induced by inlet secondary flow and geometric differences, respectively. Conclusions: The degree of variation is demonstrated to be within the range of the other computational assumptions, and we conclude that given a sufficient entrance length of realistic geometry, simplification to fully developed axial (i.e., Womersley) flow may be made without penalty. Thus, given a choice between measuring three components of inlet velocity or a greater geometric extent, we recommend effort be given to more accurate and detailed geometric reconstructions, as being of primary influence on physiologically significant indicators.

The influence of inlet velocity profile and secondary flow on pulsatile flow in a model artery with stenosis

2008 ◽  
Vol 616 ◽  
pp. 263-301 ◽  
Author(s):  
SEAN D. PETERSON ◽  
MICHAEL W. PLESNIAK
Keyword(s):  
Velocity Profile ◽  
Secondary Flow ◽  
Vortex Ring ◽  
Radial Pressure ◽  
Minor Role ◽  
Mean Velocity ◽  
Inlet Velocity ◽  
Area Reduction ◽  
Vortex Ring Formation ◽  
Inlet Conditions

The results of an experimental investigation to determine the influence of two physiologically relevant inlet conditions on the flow physics downstream of an idealized stenosis are presented. The two inlet conditions are an asymmetric mean inlet velocity profile and an asymmetric mean inlet velocity profile plus secondary flow, as found downstream of a bend. The stenosis is modelled as an axisymmetric 75% area reduction occlusion with a length-to-diameter ratio of 2. The flow was forced by a 10-harmonic carotid artery-inspired waveform with mean, maximum and minimum Reynolds numbers of 364, 1424 and 24, respectively, and a Womersley number of 4.6. Laser Doppler velocimetry and particle image velocimetry were used to characterize the spatial and temporal evolution of a baseline case (no disturbances) as well as the two physiologically relevant inlet conditions. The asymmetric inlet velocity profile was found to reduce the region of influence of the stenosis by forcing the stenotic jet towards the tube wall via an induced non-uniform radial pressure gradient, similar to the Coanda effect. Curvature-induced secondary flow was found to play a minor role in the near-stenosis region. Vortex ring formation was relatively unaffected by the mean velocity gradient and secondary flow. Evidence of remnants of the starting vortex ring was observed far downstream in all cases.

scholarly journals Effect of Inlet Velocity Profiles on Patient-Specific Computational Fluid Dynamics Simulations of the Carotid Bifurcation

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Ian C. Campbell ◽  
Jared Ries ◽  
Saurabh S. Dhawan ◽  
Arshed A. Quyyumi ◽  
W. Robert Taylor ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Carotid Bifurcation ◽  
Velocity Profiles ◽  
Patient Specific ◽  
Flow Waveform ◽  
Specific Flow ◽  
Inlet Velocity ◽  
The Mean

Patient-specific computational fluid dynamics (CFD) is a powerful tool for researching the role of blood flow in disease processes. Modern clinical imaging technology such as MRI and CT can provide high resolution information about vessel geometry, but in many situations, patient-specific inlet velocity information is not available. In these situations, a simplified velocity profile must be selected. We studied how idealized inlet velocity profiles (blunt, parabolic, and Womersley flow) affect patient-specific CFD results when compared to simulations employing a “reference standard” of the patient’s own measured velocity profile in the carotid bifurcation. To place the magnitude of these effects in context, we also investigated the effect of geometry and the use of subject-specific flow waveform on the CFD results. We quantified these differences by examining the pointwise percent error of the mean wall shear stress (WSS) and the oscillatory shear index (OSI) and by computing the intra-class correlation coefficient (ICC) between axial profiles of the mean WSS and OSI in the internal carotid artery bulb. The parabolic inlet velocity profile produced the most similar mean WSS and OSI to simulations employing the real patient-specific inlet velocity profile. However, anatomic variation in vessel geometry and the use of a nonpatient-specific flow waveform both affected the WSS and OSI results more than did the choice of inlet velocity profile. Although careful selection of boundary conditions is essential for all CFD analysis, accurate patient-specific geometry reconstruction and measurement of vessel flow rate waveform are more important than the choice of velocity profile. A parabolic velocity profile provided results most similar to the patient-specific velocity profile.

On the Relative Importance of Rheology for Image-Based CFD Models of the Carotid Bifurcation

2006 ◽  
Vol 129 (2) ◽  
pp. 273-278 ◽  
Author(s):  
Sang-Wook Lee ◽  
David A. Steinman
Keyword(s):  
Blood Rheology ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Newtonian Viscosity ◽  
Cfd Simulations ◽  
Shear Rates ◽  
Cfd Models ◽  
Geometric Precision ◽  
Simplifying Assumptions ◽  
Constant Viscosity

Background: Patient-specific computational fluid dynamics (CFD) models derived from medical images often require simplifying assumptions to render the simulations conceptually or computationally tractable. In this study, we investigated the sensitivity of image-based CFD models of the carotid bifurcation to assumptions regarding the blood rheology. Method of Approach: CFD simulations of three different patient-specific models were carried out assuming: a reference high-shear Newtonian viscosity, two different non-Newtonian (shear-thinning) rheology models, and Newtonian viscosities based on characteristic shear rates or, equivalently, assumed hematocrits. Sensitivity of wall shear stress (WSS) and oscillatory shear index (OSI) were contextualized with respect to the reproducibility of the reconstructed geometry, and to assumptions regarding the inlet boundary conditions. Results: Sensitivity of WSS to the various rheological assumptions was roughly 1.0dyn∕cm2 or 8%, nearly seven times less than that due to geometric uncertainty (6.7dyn∕cm2 or 47%), and on the order of that due to inlet boundary condition assumptions. Similar trends were observed regarding OSI sensitivity. Rescaling the Newtonian viscosity based on time-averaged inlet shear rate served to approximate reasonably, if overestimate slightly, non-Newtonian behavior. Conclusions: For image-based CFD simulations of the normal carotid bifurcation, the assumption of constant viscosity at a nominal hematocrit is reasonable in light of currently available levels of geometric precision, thus serving to obviate the need to acquire patient-specific rheological data.

The Effect of Inlet Flow Profile Simplifications in Computational Fluid Dynamics of the Carotid Bifurcation

2011 ◽  
Author(s):  
Jared Ries ◽  
Ian C. Campbell ◽  
Saurabh S. Dhawan ◽  
Arshed A. Quyyumi ◽  
W. Robert Taylor ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Flow Profile ◽  
Inlet Flow ◽  
Measured Velocity ◽  
Inlet Velocity ◽  
Parabolic Flow

Computational fluid dynamics (CFD) is emerging as a powerful tool for researching the role of blood flow in disease processes. Modern clinical imaging technology such as magnetic resonance (MR) angiography and computed tomography (CT) can provide very high resolution information about the geometry of patients’ vasculature for such modeling. However, in many situations, patient-specific inlet velocity information is not available. In these situations, a simplified velocity profile must be selected. In this study, we sought to identify how idealized inlet velocity profiles (blunt flow, parabolic flow, and Womersley flow) affect patient-specific CFD results when compared to simulations employing the real measured velocity profile for each patient. Focusing on the carotid bifurcation, a site prone to atherosclerosis because of its branching geometry and oscillatory flow patterns, we investigated the effect of inlet flow assumptions on hemodynamic parameters known to be associated with atherosclerosis and vascular disease, namely mean wall shear stress (WSS) and oscillatory shear index (OSI) [1].

scholarly journals Effect of Common Carotid Artery Inlet Length on Normal Carotid Bifurcation Hemodynamics

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Yiemeng Hoi ◽  
Bruce A. Wasserman ◽  
Edward G. Lakatta ◽  
David A. Steinman
Keyword(s):  
Carotid Artery ◽  
Common Carotid Artery ◽  
Carotid Bifurcation ◽  
Velocity Profiles ◽  
Substantial Improvement ◽  
Disturbed Flow ◽  
Inlet Velocity ◽  
Cfd Models ◽  
Inlet Length ◽  
The Impact

Controversy exists regarding the suitability of fully developed versus measured inlet velocity profiles for image-based computational fluid dynamics (CFD) studies of carotid bifurcation hemodynamics. Here, we attempt to resolve this by investigating the impact of the reconstructed common carotid artery (CCA) inlet length on computed metrics of “disturbed” flow. Twelve normal carotid bifurcation geometries were reconstructed from contrast-enhanced angiograms acquired as part of the Vascular Aging—The Link That Bridges Age to Atherosclerosis study (VALIDATE). The right carotid artery lumen geometry was reconstructed from its brachiocephalic origin to well above the bifurcation, and the CCA was truncated objectively at locations one, three, five, and seven diameters proximal to where it flares into the bifurcation. Relative to the simulations carried out using the full CCA, models truncated at one CCA diameter strongly overestimated the amount of disturbed flow. Substantial improvement was offered by using three CCA diameters, with only minor further improvement using five CCA diameters. With seven CCA diameters, the amounts of disturbed flow agreed unambiguously with those predicted by the corresponding full-length models. Based on these findings, we recommend that image-based CFD models of the carotid bifurcation should incorporate at least three diameters of CCA length if fully developed velocity profiles are to be imposed at the inlet. The need for imposing measured inlet velocity profiles would seem to be relevant only for those cases where the CCA is severely truncated.

Numerical study on the hemodynamics of patient-specific carotid bifurcation using a new mesh approach

2018 ◽  
Vol 34 (6) ◽  
pp. e2972 ◽  
Author(s):  
S.I.S. Pinto ◽  
J.B.L.M. Campos ◽  
E. Azevedo ◽  
C.F. Castro ◽  
L.C. Sousa
Keyword(s):  
Numerical Study ◽  
Carotid Bifurcation ◽  
Patient Specific

Numerical Simulation of Blood Flow in Patient-Specific Stenotic Carotid Bifurcation Geometries

2009 ◽  
Author(s):  
Megan Cummins ◽  
Jenn S. Rossmann
Keyword(s):  
Vortex Shedding ◽  
Carotid Bifurcation ◽  
Secondary Flows ◽  
Patient Specific ◽  
Mechanical Forces ◽  
Plaque Vulnerability ◽  
Governing Equations ◽  
Unstable Plaque ◽  
Recirculation Zones ◽  
Insight Into

The hemodynamics and fluid mechanical forces in blood vessels have long been implicated in the deposition and growth of atherosclerotic plaque. Detailed information about the hemodynamics in vessels affected by significant plaque deposits can provide insight into the mechanisms and likelihood of plaque weakening and rupture. In the current study, the governing equations are solved in their finite volume formulation in several patient-specific geometries. Recirculation zones, vortex shedding, and secondary flows are captured. The forces on vessel walls are shown to correlate with unstable plaque deposits. The results of these simulations suggest morphological features that may usefully supplement percent stenosis as a predictor of plaque vulnerability.

Modeling of Compressor Drum Cavities With Radial Inflow

2016 ◽  
Author(s):  
D. Amirante ◽  
Z. Sun ◽  
J. W. Chew ◽  
N. J. Hills ◽  
N. R. Atkins
Keyword(s):  
Thermal Stratification ◽  
Turbulence Modeling ◽  
Navier Stokes ◽  
Inflow Rate ◽  
Cfd Models ◽  
Flow And Heat Transfer ◽  
Rotating Discs ◽  
Computational Fluid Dynamics Cfd ◽  
Inlet Conditions ◽  
Cooling Air

Reynolds-Averaged Navier-Stokes (RANS) computations have been conducted to investigate the flow and heat transfer between two co-rotating discs with an axial throughflow of cooling air and a radial bleed introduced from the shroud. The computational fluid dynamics (CFD) models have been coupled with a thermal model of the test rig, and the predicted metal temperature compared with the thermocouple data. CFD solutions are shown to vary from a buoyancy driven regime to a forced convection regime, depending on the radial inflow rate prescribed at the shroud. At a high radial inflow rate, the computations show an excellent agreement with the measured temperatures through a transient rig condition. At a low radial inflow rate, the cavity flow is destabilized by the thermal stratification. Good qualitative agreement with the measurements is shown, although a significant over-prediction of disc temperatures is observed. This is associated with under prediction of the penetration of the axial throughflow into the cavity. The mismatch could be the result of strong sensitivity to the prescribed inlet conditions, in addition to possible shortcomings in the turbulence modeling.

Experimental Investigations and Numerical Validation of an Outlet Guide Vane With an Engine Mount Recess

2008 ◽  
Author(s):  
Johan Hja¨rne ◽  
Valery Chernoray ◽  
Jonas Larsson
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Guide Vane ◽  
Test Facility ◽  
Experimental Investigations ◽  
Flow Angle ◽  
Sst Model ◽  
Engine Mount ◽  
Inlet Conditions ◽  
Secondary Flow Field

This paper presents experiments and CFD calculations of a Low Pressure Turbine/Outlet Guide Vane (LPT/OGV) equipped with an engine mount recess (a bump) tested in the Chalmers linear LPT/OGV cascade. The investigated characteristics include performance for the design point in terms of total pressure loss and turning as well as a detailed description of the downstream development of the secondary flow field. The numerical simulations are performed for the same inlet conditions as in the test-facility with engine-like properties in terms of Reynolds number, boundary-layer thickness and inlet flow angle. The objective is to validate how accurately and reliably the secondary flow field and losses can be predicted for an LPT/OGV equipped with a bump. Three different turbulent models as implemented in FLUENT, the k-ε realizable model, the kω-SST model and the RSM are validated against detailed measurements. From these results it can be concluded that the kω-SST model predicts both the secondary flow field and the losses most accurately.

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