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"Terracol, Marc"
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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
Unsteady Turbulence Simulation on Self-Adaptive Grids
The following sections are included:
Turbulence and Self-adaptivity: Expectations and Issues
Adaptive Multilevel DNS and LES
Dynamic local multilevel LES
The dynamic multilevel (DML) method of dubois, jauberteau and temam
Spectral multilevel decomposition
Associated Navier–Stokes-based equations
Quasi-static approximation
General description of the spectral multilevel method
Dynamic estimation of the parameters i1, i2 and nV
Dynamic global multilevel LES
Adaptive Wavelet-based Methods: CVS, SCALES
Wavelet decomposition: brief reminder
Coherency diagram of a turbulent field
Introduction to the coherency diagram
Threshold value and error control
Adaptive wavelet-based direct numerical simulation
Coherent vortex capturing method
Stochastic coherent adaptive large-eddy simulation
DNS and LES with Optimal AMR
Error definition: surfacic versus volumic formulation
A posteriori error estimation and optimization loop
Numerical results
Reference
Global Hybrid RANS/LES Methods
The following sections are included:
Bridging between Hybrid RANS/LES Methods and Multiscale Methods
Concept: the effective filter
Eddy viscosity effective filter
Global hybrid RANS/LES methods asmultiscale methods
Motivation and Classification of RANS/LES Methods
Unsteady Statistical Modelling Approaches
Unsteady RANS approach
The Semi-Deterministic Method of Ha Minh
The Scale Adaptive Simulation (SAS)
The Turbulence-Resolving RANS approach of Travin et al
Global Hybrid Approaches
The Approach of Speziale
Limited Numerical Scales (LNS)
General idea of LNS
Example of application
Blending methods
General idea of blending methods
Applications
Other approaches: PITM and PANS
Partially Integrated Transport Model (PITM)
Partially Averaged Navier–Stokes (PANS)
Detached Eddy Simulation
General idea
DES based on the SA model
Possible extensions of standard SA-DES
Examples
DES based on the k – ω model
Extra-Large Eddy Simulation (XLES)
Grey-Area Modelled-Stress-Depletion (MSD) Grid and Induced Separation (GIS)
Further interpretation of MSD: non-local error analysis
Delayed Detached Eddy Simulation (DDES)
Formulation
Improved Delayed Detached Eddy Simulation (IDDES)
Zonal Detached Eddy Simulation (ZDES)
Formulation
Implementation
Interpretation and further discussion
Reference