Flame transfer function and disturbance energies in gaseous reacting flows

The general objective of this thesis is to extend the understanding of combustion instabilities by testing models, physical concepts and numerical procedures, and by providing new numerical post-processing tools to do so. Flame transfer function (FTF) : four different methods for the determination of flame transfer functions (FTFs) in LES have been tested. A new method based on the forcing of the flame by a filtered white noise is used to obtain the FTF at all frequencies with only one unsteady LES. Disturbance energies and stability criteria in reacting flows : two stability criteria in reacting flows are derived. The first one extends teh Rayleigh criterion by taking into account the influence of the heat flux fluctuation. The second criterion is nonlinear and is based on the analysis of the budjet of a newly derived nonlinear disturbance energy during a controled thermo-acoustic instabilit

Large Eddy Simulation of an axial compressor rotor passage: Preliminary comparison with experimental measurements

Ce résumé étendu présente les résultats préliminaires issus de la comparaison entre la Simulation aux Grandes Echelles et la mesure expérimentale de l'écoulement dans un passage inter-aubes de rotor axial.This extended abstract presents preliminary results of the comparison between Large Eddy Simulation and experimental measurements of the flow in an axial rotor passage

A nonlinear model for indirect combustion noise through a compact nozzle

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Fonctions de transfert de flamme et énergies des pertubations dans les écoulements réactifs

The general objective of this thesis is to extend the understanding of combustion instabilities by testing models, physical concepts and numerical procedures, and by providing new numerical post-processing tools to do so. Flame Transfert Function (FTF) : four methods for the determination of Flame Transfer Functions (FTFs) in LES have been tested. A new method based on the forcing of the flame by a filtered white noise is used to obtain the FTF at all frequencies with only one unsteady LES. Disturbance Energies and Stability Criteria in reacting Flows : two stability criteria in reacting flows are derived. The first one extends the Rayleigh criterion by taking into account the influence of the heat flux fluctuation. The second criterion is nonlinear and is based on the analysis of the budjet of a newly derived nonlinear disturbance energy during a controled thermo-acoustic instability.L'objectif de cette thèse est d'étendre la compréhension des instabilités de combustion en testant des modèles, des concepts physiques, des méthodes numériques ainsi qu'en fournissant de nouveaux outils numériques pour y parvenir. Fonctions de Transfert de Flamme (FTF) : quatre méthodes numériques de détermination de la FTF grâce à la Simulation aux Grandes Échelles (SGE) sont testées. Une nouvelle méthode reposant sur le forçage de la chambre de combustion par un bruit blanc filtré est utilisée pour obtenir la FTF à toutes les fréquences grâce à un unique calcul SGE. Énergies des Perturbations et Critères de stabilité en Combustion : deux critères de stabilité en combustion sont proposés. Le premier étend le critère de Rayleigh en introduisant l'influence de la fluctuation du flux de chaleur. Le second critère est nonlinéaire et repose sur l'analyse du bilan d'une nouvelle énergie nonlinéaire des perturbations au cours d'un cycle d'instabilité thermo-acoustique contrôlée.TOULOUSE-INP (315552154) / SudocSudocFranceF

Direct numerical simulations of temporal compressible mixing layers in a BZT dense gas: influence of the convective Mach number

International audienceThe present article investigates the effects of a BZT (Bethe-Zel'dovich-Thompson) dense gas (FC-70) on the development of turbulent compressible mixing layers at three different convective Mach numbers M c = 0.1, 1.1 and 2.2. This study extends a previous analysis conducted at M

Direct numerical simulations of homogeneous isotropic turbulence in a dense gas

International audienceA study of turbulence in BZT dense gas flows is performed using DNS. It is shown that for a large but realistic intensity, the turbulence in dense gas flows behaves in a highly compressible manner when the average thermodynamic state lies within the inversion region in which the gas fundamental derivative is negative. A close similarity is observed in the evolution of the kinetic energy when the initial turbulent Mach number and the Taylor Reynolds number are matched regardless of the Equation of State (EoS) considered. A large turbulent Mach number is yet more easily attained in dense gas flows lying in the inversion region because of the low speed of sound associated with it. In this case the turbulence shows a highly compressible evolution with periodic exchanges between the internal and kinetic energies. In order to assess the capabilities of currently available Large Eddy Simulation (LES) subgrid-scale models, a-posteriori tests are performed using the dynamic Smagorinsky model. Coherently with the hypothesis it relies on, the model perfectly captures the evolution of the kinetic energy when the turbulent Mach number is low enough. When using the perfect gas EoS at a higher turbulent Mach number the agreement is reasonable. Yet, when the average thermodynamic state lies within the inversion region and when using the thermal and caloric Martin&Hou EoS, the model is not able to capture the correct evolution of the kinetic energy. The results presented in this study call for a specific research effort directed towards the assessment and possibly the development of advanced subgrid-scale models for LES of turbulent dense gas flows

Towards Subgrid-Scale Turbulence Modeling in Dense Gas Flows

International audienceIt is known from the literature that Large Eddy Simulations of dense gas flows can prove very useful in order to better understand the behavior of friction losses in Organic Rankine Cycle turbines and expanders. Yet, no dedicated turbulence closure models exist for such flows. In this study, the authors lay the fondations for the development of turbulence closure models in dense gas flows. The Subgrid-Scale terms are first rigorously derived from the filtered Navier-Stokes equations. Additional terms to the well-known Subgrid-Scale closure terms are identified in the dense gas context. Using Direct Numerical Simulation, the variances of Subgrid-Scale terms in the filtered momentum equations are computed both for the dense and perfect gas cases and significant differences are revealed between the two cases. A model using only filtered fields as input is derived for one of the dense gas specific Subgrid-Scale terms using a Correlation Patterns Modeling approach. Preliminary a priori tests indicate that this approach can be easily implemented and provides promising results

A 2D-axisymmetric analytical model for the estimation of indirect combustion noise in nozzle flows

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Thermoacoustic Shape Optimization of a Subsonic Nozzle

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