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Application of vortex identification schemes to direct numerical simulation data of a transitional boundary layer
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In this paper, the authors have demonstrated how various vortex identification and visualization criteria perform using direct numerical simulation data from a transitional and turbulent boundary layer by Sayadi, Hamman, and Moin.Abstract:
We have demonstrated how various vortex identification and visualization criteria perform using direct numerical simulation data from a transitional and turbulent boundary layer by Sayadi, Hamman, and Moin [“Direct numerical simulation of complete transition to turbulence via h-type and k-type secondary instabilities,” Technical Report, Stanford University, CTR Annual Research Briefs, 2011]. The presence of well-known Λ vortices in the transitional region provides a well defined and yet realistic benchmark for evaluation of various criteria. We investigate the impact of changing the threshold used for iso-surface plotting.read more
Citations
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New omega vortex identification method
TL;DR: In this paper, a new vortex identification criterion called W -method is proposed based on the ideas that vorticity overtakes deformation in vortex and W = 0.52 is a quantity to approximately define the vortex boundary.
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Direct numerical simulation of complete H-type and K-type transitions with implications for the dynamics of turbulent boundary layers
TL;DR: In this article, the onset and development of turbulence from controlled disturbances in compressible ( ), flat-plate boundary layers is studied by direct numerical simulation, and it is shown that H- and K-type breakdowns both relax toward the same statistical structure typical of developed turbulence at high Reynolds number immediately after the skin-friction maximum.
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Determination of epsilon for Omega vortex identification method
TL;DR: In this article, epsilon (e) in the Omega vortex identification criterion (Ω method) is defined as an explicit function in order to apply the Ω method to different cases and even different time steps for the unsteady cases.
Journal ArticleDOI
A stochastic perturbation method to generate inflow turbulence in large-eddy simulation models: Application to neutrally stratified atmospheric boundary layers
TL;DR: In this article, a stochastic approach based on finite amplitude perturbations of the potential temperature field applied within a region near the inflow boundaries of the large-eddy simulation (LES) domain is proposed.
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Building proper invariants for eddy-viscosity subgrid-scale models
TL;DR: In this article, the authors propose a method for the extraction of the structure of the human brain from the data of a neural network, which can be used to predict the future of neural networks.
References
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Journal ArticleDOI
On the identification of a vortex
Jinhee Jeong,Fazle Hussain +1 more
TL;DR: In this article, the authors propose a definition of vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor, which captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers.
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Mechanisms for generating coherent packets of hairpin vortices in channel flow
TL;DR: In this article, the evolution of a single hairpin vortex-like structure in the mean turbulent field of a low-Reynolds-number channel flow is studied by direct numerical simulation, and the detailed mechanisms for this upstream process are determined, and they are generally similar to the mechanisms proposed by Smith et al. (1991), with some notable differences in the details.
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A general classification of three-dimensional flow fields
TL;DR: In this paper, the geometry of solution trajectories for three first-order coupled linear differential equations can be related and classified using three matrix invariants for elementary three-dimensional flow patterns defined by instantaneous streamlines for flow at and away from no slip boundaries for both compressible and incompressible flow.
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The three-dimensional nature of boundary-layer instability
TL;DR: In this article, an experimental investigation is described, in which principal emphasis is given to revealing the nature of the motions in the non-linear range of boundary-layer instability and the onset of turbulence, and it is demonstrated that the actual breakdown of the wave motion into turbulence is a consequence of a new instability which arises in the aforementioned three-dimensional wave motion.
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On the relationships between local vortex identification schemes
TL;DR: In this paper, a new measure of spiralling compactness of material orbits in vortices is introduced and using this measure a new local vortex identification criterion and requirements for a vortex core are proposed.