Asymmetry and transition to turbulence in a smooth axisymmetric constriction

Vétel, Jérôme; Garon, André; Pelletier, Dominique; Farinas, Marie-Isabelle

doi:10.1017/s0022112008002188

Cited by 57 publications

(61 citation statements)

References 36 publications

(62 reference statements)

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“…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%

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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: Domain Sizementioning

confidence: 99%

“…This blockage ratio of 75% represents the threshold of clinical significance and visibility using present technology. 7 The radius can be written as…”

Section: A Problem Setupmentioning

confidence: 99%

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

2015

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“…Recently, Vetel et al 8 experimentally investigates transition to turbulence in a pipe geometry having a smooth axisymmetric constriction. When the Reynolds number is increased above the critical value of 200, an unsteady flow occurs with low-frequency oscillations of the reattachment point and the shedding of vortices.…”

Section: A Vortex Shedding Phenomenamentioning

confidence: 99%

“…The boundary and initial conditions, (8) and (9), are similarly transformed into computational coordinates through the use of (10). Thus, the boundary conditions at the bottom and top of the computational domain are…”

Section: Coordinate Transformationmentioning

confidence: 99%

“…[1][2][3][4][5] Recently, this vortex shedding phenomenon has been observed in numerical simulations and experiments on the hemodynamics of stenosed blood vessels. [6][7][8] The vortex shedding phenomenon is important because it significantly impacts surface forces, can affect local mass transfer rates, generates vibrations, and it is expected that breakdown of shed vortices plays a critical role in transition to turbulence. 9 Real flows in channel geometries are typically three-dimensional, particularly at high Reynolds numbers.…”

Section: Introductionmentioning

confidence: 99%

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A pressure-gradient mechanism for vortex shedding in constricted channels

Boghosian

Cassel

2013

Physics of Fluids

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Numerical simulations of the unsteady, two-dimensional, incompressible NavierStokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier-Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability, leads to the vortex shedding phenomenon via a proposed streamwise pressure-gradient mechanism. C 2013 AIP Publishing LLC. [http://dx

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Laminar‐to‐turbulent fluid–nanoparticle dynamics simulations: Model comparisons and nanoparticle‐deposition applications

Zhang

Kleinstreuer

2011

Numer Methods Biomed Eng

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SUMMARYRelying on benchmark experimental data sets for flow in conduits with local constrictions, LES and three widely used RANS turbulence models, i.e. the low Reynolds number (LRN) k-model, standard k-model and shear stress transport (SST) transition model, were compared and evaluated to gain new physical insight and provide useful turbulence modeling information. These two geometric test cases may represent stenosed arteries and a segment of the human upper airways where the velocity fields undergo all flow regimes, i.e. from laminar, via transitional, to fully turbulent.The comparison study revealed that the standard k-models amplify the flow instabilities after the constrictions, and hence fail to capture the laminar flow behavior at relatively LRNs. The overall performances of LES, the LRN k-model and SST transition model do not have measurable differences in predicting laminar flows and transition to turbulent flow, while the SST transition model may give a better prediction of turbulence kinetic energy profiles in some cases. Clearly, LES can provide instantaneous velocity fluctuations, which may be significant for turbulent micron particle transport/deposition in the respiratory tract. However, it requires 100-fold more computational time than RANS turbulence models. The use of different turbulence models has a minor effect on nanoparticle deposition in human upper airways when the inspiratory flow rate is low, say, Q = 10 L/min. The relative difference for deposition fraction (DF) of nanoparticles with d p > 10 nm is measurable at a medium inhalation flow rate (say, Q = 30 L/min) when employing different turbulence models. However, the absolute difference in DFs is within 0.5% for all-sized nanoparticles (i.e. 1 nm d p 50 nm) because the DF in the oral airway is very low (say, < 1.5%) when d p 10 nm and Q 10 L/min.The modeling and simulation information provided are most useful for computational fluid-particle dynamics practitioners to obtain accurate lung deposition concentrations of inhaled toxic or therapeutic nanoparticles. The physical insight provided sheds additional light on the laminar-to-turbulent airflow and nanoparticle transport/deposition in locally constricted conduits.

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Asymmetry and transition to turbulence in a smooth axisymmetric constriction

Cited by 57 publications

References 36 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

A pressure-gradient mechanism for vortex shedding in constricted channels

Laminar‐to‐turbulent fluid–nanoparticle dynamics simulations: Model comparisons and nanoparticle‐deposition applications

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