Joint numerical and experimental study of thermo-acoustic instabilities
Soutenance de thèse Maxence Brebion
Sous réserve d’autorisation de soutenance par les rapporteurs
Vendredi 27 janvier
Amphithéâtre Nougaro à 14h 00
From small scale energy systems such as domestic boilers up to rocket motors, combustion chambers are often prone to combustion instabilities. These instabilities stem from the coupling of unsteady heat release rate and acoustic waves. This coupling is two sided : flame front perturbations generate acoustic waves while acoustic waves impinging on flame holders can disturb flames attached on them. Important pressure and velocity oscillations can be reached during unstable regimes, that can alter its efficiency or even damage the entire combustion chamber. One major challenge is to understand, predict, and prevent from these combustion instabilities. The objectives of this thesis are twofold : (1) take into account acoustic dissipation and (2) analyze flame/acoustic coupling to obtain Reduced Order Model (ROM) for combustion instabilities.
This work is divided into three parts. First, the concept of ROM that gives the acoustic modes of a combustion chamber is introduced. This modeling strategy is based on the acoustic network theory and may take into account flame/acoustic coupling as well as acoustic dissipation. An efficient numerical algorithm dedicated to solve ROMs was designed on purpose and validated on several academical configurations. Second, an experimental rig was commissioned to study mean and acoustic pressure losses across a diaphragm and two swirl injectors. Results show that these two phenomena are linked and can be simply incorporated into ROMs. Finally, flame/acoustic coupling is investigated by using both direct numerical simulations and experiments : a lean premixed V-shaped laminar flame is anchored on a cylindrical bluff-body and we show that its temperature greatly influences the flame mean shape as well as its dynamics.
- Thierry Schuller Professeur (EM2C) Rapporteur
- Wolfgang Polifke Professeur (Technische Universitat Munchen) Rapporteur
- Christophe Bailly Professeur (Centre Acoustique, EC-Lyon) Examinateur
- Franck Nicoud Professeur ( IMAG, Montpellier) Examinateur
- Thierry Poinsot Directeur de Recherche (CNRS) (IMFT) Directeur de thèse
- Laurent Selle Chargée de Recherche (CNRS) (IMFT) Co-directeur de thèse