Effect of small asymmetries on axisymmetric stenotic flow

Griffith, Martin D.; Leweke, Thomas; Thompson, Mark C.; Hourigan, Kerry

doi:10.1017/jfm.2013.109

Cited by 33 publications

(18 citation statements)

References 19 publications

(42 reference statements)

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“…That same discontinuity was found in this study, occurring at E ≈ 0.27% and E ≈ 0.17% for Re = 350 and Re = 400, respectively. Maximum flow asymmetryμ y for Re = 350 and E = 0.1% wasμ y ≈ 0.019, found at z ≈ 4.3, 12 in agreement with the present study, which findsμ y = 0.0189 at z = 4.34. Stability analysis performed around E = 0 gives the same leading eigenmode as that found by Sherwin and Blackburn.…”

Section: Validationsupporting

confidence: 93%

“…As Figure 3(b) shows, when eccentricity is increased beyond a certain value E 0 , e.g., E 0 = 0.27% for Re = 350 and E 0 = 0.17% for Re = 400, the flow asymmetry increases abruptly, which was also noted by Griffith et al 12 Thus, the flow can be divided into two regimes: branch 1, with the minor flow asymmetry and branch 2 with the greater flow asymmetry. The physics of this new flow regime, branch 2, is largely the same: the flow also exhibits a Coanda type wall attachment to the upper side, but the flow separates further upstream in branch 2 than branch 1, which leads to an increase in flow asymmetry in the post-stenotic region.…”

Section: A Dns With a Flow At Rest As Initial Conditionsupporting

confidence: 70%

“…Vétel et al 7 116-1160 0 Ahmed and Giddens 6 500,1000 0 Griffith et al 8 50-2500 0 N/A 81D Sherwin and Blackburn 9 400-800 0 38 000 50D Griffith et al 12 1-400 0-5 200 000 31D Varghese, Frankel, and Fischer 11 Griffith et al 12 performed a numerical DNS study and showed that the discrepancy in the steady flow regime between the experimental results reported by Vétel et al 7 and the numerical investigations can be accredited to non-axisymmetric changes in the stenosis' shape, inherent in all experimental systems. However, the investigated Reynolds number ranged from Re = 1 to 400 and thus did not cover the non-stationary flow regime, nor was any stability analysis performed.…”

Section: Domain Sizementioning

confidence: 99%

“…The deflection of the jet can be described by tracking flow asymmetry, µ y , as a function of the streamwise coordinate, as was done by Griffith et al 12 using the normalized first moment of the streamwise velocity component,…”

Section: Definitionsmentioning

confidence: 99%

“…The DNS code was validated against results from Griffith et al 12 Griffith et al 12 noticed a discontinuity in the asymmetry of the flow when varying eccentricity at around E ≈ 0.25% and E ≈ 0.18%(±0.02%) for Re = 350 and Re = 400, respectively. That same discontinuity was found in this study, occurring at E ≈ 0.27% and E ≈ 0.17% for Re = 350 and Re = 400, respectively.…”

Section: Validationmentioning

confidence: 99%

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Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

2015

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Flow through a sinuous stenosis with varying degrees of non-axisymmetric shape variations and at Reynolds number ranging from 250 to 750 is investigated using direct numerical simulation (DNS) and global linear stability analysis. At low Reynolds numbers (Re < 390), the flow is always steady and symmetric for an axisymmetric geometry. Two steady state solutions are obtained when the Reynolds number is increased: a symmetric steady state and an eccentric, non-axisymmetric steady state. Either one can be obtained in the DNS depending on the initial condition. A linear global stability analysis around the symmetric and non-axisymmetric steady state reveals that both flows are linearly stable for the same Reynolds number, showing that the first bifurcation from symmetry to antisymmetry is subcritical. When the Reynolds number is increased further, the symmetric state becomes linearly unstable to an eigenmode, which drives the flow towards the non-axisymmetric state. The symmetric state remains steady up to Re = 713, while the non-axisymmetric state displays regimes of periodic oscillations for Re ≥ 417 and intermittency for Re 525. Further, an offset of the stenosis throat is introduced through the eccentricity parameter E. When eccentricity is increased from zero to only 0.3% of the pipe diameter, the bifurcation Reynolds number decreases by more than 50%, showing that it is highly sensitive to non-axisymmetric shape variations. Based on the resulting bifurcation map and its dependency on E, we resolve the discrepancies between previous experimental and computational studies. We also present excellent agreement between our numerical results and previous experimental results. C 2015 AIP Publishing LLC.

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Section: Validationsupporting

confidence: 93%

Section: A Dns With a Flow At Rest As Initial Conditionsupporting

confidence: 70%

Section: Domain Sizementioning

confidence: 99%

Section: Definitionsmentioning

confidence: 99%

Section: Validationmentioning

confidence: 99%

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Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

2015

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The FDA nozzle benchmark: “In theory there is no difference between theory and practice, but in practice there is”

Bergersen

Mortensen

Valen‐Sendstad

2018

Numer Methods Biomed Eng

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The utility of flow simulations relies on the robustness of computational fluid dynamics (CFD) solvers and reproducibility of results. The aim of this study was to validate the Oasis CFD solver against in vitro experimental measurements of jet breakdown location from the FDA nozzle benchmark at Reynolds number 3500, which is in the particularly challenging transitional regime. Simulations were performed on meshes consisting of 5, 10, 17, and 28 million (M) tetrahedra, with Δt = 10 seconds. The 5M and 10M simulation jets broke down in reasonable agreement with the experiments. However, the 17M and 28M simulation jets broke down further downstream. But which of our simulations are "correct"? From a theoretical point of view, they are all wrong because the jet should not break down in the absence of disturbances. The geometry is axisymmetric with no geometrical features that can generate angular velocities. A stable flow was supported by linear stability analysis. From a physical point of view, a finite amount of "noise" will always be present in experiments, which lowers transition point. To replicate noise numerically, we prescribed minor random angular velocities (approximately 0.31%), much smaller than the reported flow asymmetry (approximately 3%) and model accuracy (approximately 1%), at the inlet of the 17M simulation, which shifted the jet breakdown location closer to the measurements. Hence, the high-resolution simulations and "noise" experiment can potentially explain discrepancies in transition between sometimes "sterile" CFD and inherently noisy "ground truth" experiments. Thus, we have shown that numerical simulations can agree with experiments, but for the wrong reasons.

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Direct numerical simulation of a pulsatile flow in a stenotic channel using immersed boundary method

Mirfendereski

Park

2021

Engineering Reports

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A three-dimensional direct numerical simulation model coupled with the immersed boundary method has been developed to simulate a pulsatile flow in a planar channel with single and double one-sided semicircular constrictions. For relevance to blood flow in large arteries, simulations have been performed at Reynolds numbers of 750 and 1000. Flow physics and resultant wall shear stress (WSS)-based hemodynamic parameters are presented. The instantaneous vortex dynamics, mean flow characteristics, and turbulent energy spectra are evaluated for flow physics. Subsequently, three WSS-based parameters, namely the time-averaged WSS, oscillatory shear index, and relative residence time, are calculated over the stenotic wall and correlated with flow physics to identify the regions prone to atherosclerotic plaque progression. Results show that the double stenotic channel leads to high-intensity and broadband turbulent characteristics downstream, promoting critical values of the WSS-based parameters in the post-stenotic areas. In addition, the inter-space area between two stenoses displays multiple strong recirculations, making this area highly prone to atherosclerosis progression. The effect of stenosis degree on the WSS-based parameters is studied up to 60% degree. As the degree of occlusion is increased, larger regions are involved with the nonphysiological ranges of the WSS-based parameters.

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Effect of small asymmetries on axisymmetric stenotic flow

Cited by 33 publications

References 19 publications

Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

Breaking axi-symmetry in stenotic flow lowers the critical transition Reynolds number

The FDA nozzle benchmark: “In theory there is no difference between theory and practice, but in practice there is”

Direct numerical simulation of a pulsatile flow in a stenotic channel using immersed boundary method

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