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"Marc Terracol"
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Nonlinear global modes in hot jets
Since the experiments of Monkewitz et al. (J. Fluid Mech. vol. 213, 1990, p. 611), sufficiently hot circular jets have been known to give rise to self-sustained synchronized oscillations induced by a locally absolutely unstable region. In the present investigation, numerical simulations are carried out in order to determine if such synchronized states correspond to a nonlinear global mode of the underlying base flow, as predicted in the framework of Ginzburg–Landau model equations. Two configurations of slowly developing base flows are considered. In the presence of a pocket of absolute instability embedded within a convectively unstable jet, global oscillations are shown to be generated by a steep nonlinear front located at the upstream station of marginal absolute instability. The global frequency is given, within 10% accuracy, by the absolute frequency at the front location and, as expected on theoretical grounds, the front displays the same slope as a $k^-$-wave. For jet flows displaying absolutely unstable inlet conditions, global instability is observed to arise if the streamwise extent of the absolutely unstable region is sufficiently large: while local absolute instability sets in for ambient-to-jet temperature ratios $S \\le 0.453$, global modes only appear for $S \\le 0.3125$. In agreement with theoretical predictions, the selected frequency near the onset of global instability coincides with the absolute frequency at the inlet. For lower $S$, it gradually departs from this value.
Journal Article
Multiscale and multiresolution approaches in turbulence
This unique book gives a general unified presentation of the use of the multiscale/multiresolution approaches in the field of turbulence. The coverage ranges from statistical models developed for engineering purposes to multiresolution algorithms for the direct computation of turbulence. It provides the only available up-to-date reviews dealing with the latest and most advanced turbulence models (including LES, VLES, hybrid RANS/LES, DES) and numerical strategies.
eBook
Multiscale and multiresolution approaches in turbulence : LES, DES and hybrid RANS/LES methods : applications and guidelines
The book aims to provide the reader with an updated general presentation of multiscale/multiresolution approaches in turbulent flow simulations. All modern approaches (LES, hybrid RANS/LES, DES, SAS) are discussed and recast in a global comprehensive framework. Both theoretical features and practical implementation details are addressed. Some full scale applications are described, to provide the reader with relevant guidelines to facilitate a future use of these methods.
Sample Chapter(s)
eBook
Multiscale and multiresolution approaches in turbulence
The book aims to provide the reader with an updated general presentation of multiscale/multiresolution approaches in turbulent flow simulations. All modern approaches (LES, hybrid RANS/LES, DES, SAS) are discussed and recast in a global comprehensive framework. Both theoretical features and practical implementation details are addressed. Some full scale applications are described, to provide the reader with relevant guidelines to facilitate a future use of these methods.
eBook
Multiscale Subgrid Models: Self-Adaptivity
The following sections are included:
Fundamentals of Subgrid Modelling
Functional and structural subgrid models
The Gabor–Heisenberg curse
Germano-type Dynamic Subgrid Models
Germano identity
Two-level multiplicative Germano identity
Multilevel Germano identity
Generalized Germano identity
Derivation of dynamic subgrid models
Dynamic models and self-similarity
Turbulence self-similarity
Scale separation operator self-similarity
Self-Similarity Based Dynamic Subgrid Models
Terracol–Sagaut procedure
Shao procedure
Variational Multiscale Methods and Related Subgrid Viscosity Models
Hughes VMS approach and extended formulations
Implementation of the scale separation operator
Bridging with hyperviscosity and filtered models
Reference
Feedback from Numerical Experiments
The following sections are included:
Flow Physics Classification and Modelling Strategy Suitability
Illustrative Examples
Practical industrial applications
Wall turbulence simulation
Further Discussion
Numerical discretization effects
General statement
Grid resolution requirements
More detailed discussion: classical LES
Zonal vs. non-zonal treatment of turbulence
Reference
A Brief Introduction to Turbulence
The following sections are included:
Common Features of Turbulent Flows
Introductory concepts
Randomness and coherent structure in turbulent flows
Turbulent Scales and Complexity of a Turbulent Field
Basic equations of turbulent flow
Defining turbulent scales
A glimpse at numerical simulations of turbulent flows
Inter-scale Coupling in Turbulent Flows
The energy cascade
Inter-scale interactions
Reference