New visualization method for vortex structure in turbulence by lambda2 and vortex filaments

Dong, Yinlin; Yan, Ya; Liu, Chaoqun

doi:10.1016/j.apm.2015.04.059

Cited by 29 publications

(7 citation statements)

References 27 publications

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“…To describe vortical flow structures in the aorta, the λ 2 criterion for incompressible flows was evaluated and displayed as isosurfaces running through the fluid domain [ 30 , 31 , 32 ]. The λ 2 criterion can be expressed as:

where λ 2 is the second eigenvalue of the tensor S 2 + Ω 2 , with S and Ω being the symmetric and antisymmetric parts of the velocity gradient tensor, respectively.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Haemodynamic Analysis of Branched Endografts for Complex Aortic Arch Repair

Sengupta

Hamady

2022

Bioengineering

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This study aims to investigate the haemodynamic response induced by implantation of a double-branched endograft used in thoracic endovascular aortic repair (TEVAR) of the aortic arch. Anatomically realistic models were reconstructed from CT images obtained from patients who underwent TEVAR using the RelayPlus double-branched endograft implanted in the aortic arch. Two cases (Patient 1, Patient 2) were included here, both patients presented with type A aortic dissection before TEVAR. To examine the influence of inner tunnel branch diameters on localised flow patterns, three tunnel branch diameters were tested using the geometric model reconstructed for Patient 1. Pulsatile blood flow through the models was simulated by numerically solving the Navier–Stokes equations along with a transitional flow model. The physiological boundary conditions were imposed at the model inlet and outlets, while the wall was assumed to be rigid. Our simulation results showed that the double-branched endograft allowed for the sufficient perfusion of blood to the supra-aortic branches and restored flow patterns expected in normal aortas. The diameter of tunnel branches in the device plays a crucial role in the development of flow downstream of the branches and thus must be selected carefully based on the overall geometry of the vessel. Given the importance of wall shear stress in vascular remodelling and thrombus formation, longitudinal studies should be performed in the future in order to elucidate the role of tunnel branch diameters in long-term patency of the supra-aortic branches following TEVAR with the double-branched endograft.

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where λ 2 is the second eigenvalue of the tensor S 2 + Ω 2 , with S and Ω being the symmetric and antisymmetric parts of the velocity gradient tensor, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…To describe vortical flow structures in the aorta, the λ 2 criterion for incompressible flows was evaluated and displayed as isosurfaces running through the fluid domain [30][31][32]. The λ 2 criterion can be expressed as:…”

Section: Haemodynamic Metricsmentioning

confidence: 99%

Haemodynamic Analysis of Branched Endografts for Complex Aortic Arch Repair

Sengupta

Hamady

2022

Bioengineering

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“…Ring-like vortical structure is observed in all cases. To visualize the vortex structures in the field, the 2 λ method [22,23] is used to capture the iso-surfaces of vortices. In this method, 2 λ is the second eigenvalue of the 3 × 3 matrix comprised of velocity gradient, i.e., Ω Ω + = : : S S M (7) where the 3 × 3 tensors…”

Section: Ring-like Vortices Generated By Mvgmentioning

confidence: 99%

Investigation of Shock-Boundary Layer Interaction in a Ramp Flow with MVG Under Different Turbulent Inflows

Yan

Chen

Cotton

et al. 2018

GJES

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MVG (micro vortex generator) is a potentially new device which can alleviate or overcome the adverse effects of SBLI (Shockboundary layer interaction) and improve the "health" of the boundary layer. In this paper, the SBLI in a ramp flow with MVG under different inflow conditions is investigated by LES (large eddy simulation). Three turbulent inflows with different boundary layer thickness are generated based on turbulent profiles obtained from DNS (Direct numerical simulation) of transition. The numerical results show that the interaction between ring-like vortices generated by MVG and the ramp shock is influenced by these different inflow conditions. With lower boundary layer thickness, the ring-like vortices are less distorted and thus more stronger when they travel to the ramp corner. The more regular and stronger ring-like vortices have more capability to eliminate or distort the strong ramp shock wave. Moreover, it confirms that ring-like vortices generated by MVG, and not the lower turbulent boundary layer, is dominant in flow separation reduction.

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“…To eliminate the contamination of shear effect (Cucitore et al, 1999;Kolář, 2010), recent local approaches turn to other indicators based the velocity gradient tensor, e.g., Δ (Chong et al, 1990), Q (Hunt et al, 1988), λ2 (Jeong and Hussain, 1995), λci (Zhou et al, 1999), and Ω (Liu et al, 2016;Zhang et al, 2018). While these indicators are useful in quantifying vortex strength, it is still difficult to select a proper universal threshold for them in nonuniform flows where vortices exhibit a broad spectrum of variation in size and strength, e.g., a higher value may lead to blurring of weaker vortices, and conversely, a lower one may result in cluttering of stronger vortices (Dong et al, 2016). Such difficulty has been partially overcome by normalization of the average indicator with its root-mean-square in cases where enough samples of the flow are available for statistical analysis (Cao et al, 2017;Chen et al, 2014b;Wu and Christensen, 2006;Zhong et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…A combination of the advantages of local and global approaches provides a new way to enhance the effectiveness of vortex extraction. Dong et al (2016), for instance, developed a λ2-scheme coupled with vortex filaments and accurately found the vortex structure. Unfortunately, this method cannot be used for identifying spanwise vortex as calculation of the vortex filaments is impossible in the two-dimensional velocity field.…”

Section: Introductionmentioning

confidence: 99%

A new method for extracting spanwise vortex from 2D particle image velocimetry data in open-channel flow

Zhang

Yang

et al. 2020

Journal of Hydrology and Hydromechanics

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The two-dimensional particle image velocimetry (PIV) data are inevitably contaminated by noise due to various imperfections in instrumentation or algorithm, based on which the well-established vortex identification methods often yield noise or incomplete vortex structure with a jagged boundary. To make up this deficiency, a novel method was proposed in this paper and the efficiency of the new method was demonstrated by its applications in extracting the two-dimensional spanwise vortex structures from 2D PIV data in open-channel flows. The new method takes up a single vortex structure by combining model matching and vorticity filtering, and successfully locates the vortex core and draws a streamlined vortex boundary. The new method shows promise as being more effective than commonly used schemes in open-channel flow applications.

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New visualization method for vortex structure in turbulence by lambda2 and vortex filaments

Cited by 29 publications

References 27 publications

Haemodynamic Analysis of Branched Endografts for Complex Aortic Arch Repair

Haemodynamic Analysis of Branched Endografts for Complex Aortic Arch Repair

Investigation of Shock-Boundary Layer Interaction in a Ramp Flow with MVG Under Different Turbulent Inflows

A new method for extracting spanwise vortex from 2D particle image velocimetry data in open-channel flow

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