PhD defense - C. Sensiau

Numerical simulations of thermoacoustic instabilities in annular combustion chambers

Delivered by University of Montpellier II
Speciality: Mathematics

October 16, 2008 - CERFACS

Thermoacoustic instabilities are spontaneously excited by a feedback loop between an oscillatory combustion process and one of the natural acoustic modes of the combustor. This phenomenon causes loss of performance and severe damages to the engine. However, aeronautical engines or gas turbines manufacturers often observe this kind of instabilities during the experiments. In this work we propose a methodology dedicated to the computation of thermoacoustic instabilities usable in an industrial context. The coupling between acoustics and combustion is accounted for thanks to a specific Helmholtz equation including a reacting flow term. Using a finite element approach leads to an algebraic non-linear eigenvalue problem with N dimensions (N the number of nodes in the mesh). A point fix algorithm mixed with subspace iterative methods (Arnoldi implemented in ARPACK or Jacobi-Davidson) permits to solve this problem efficiently. Because aeronautical combustors usually present an annular shape with 10 to 20 injectors located all over the circumference, a multi-referenced (n-?) flame transfer function is proposed. This thermoacoustic model shows amplified or damped, standing or spinning azimuthal modes depending on the parameter ?. This methodology is integrated in the calculation chain QUIET (AVBPN3S-NOZZLE-AVSP) and it is used to study thermoacoustic instabilities of a Turbomeca engine. The results are shown to be in good accordance with large eddy simulations of the whole combustor.

L. Giraud	Professor - ENSEEIHT, Toulouse	Referee
A. Hirschberg	Professor - Technische Universiteit, Eindhoven	Referee
J. Droniou	Professor - University of Montpellier II	Referee
S. Ducruix	Researcher - Ecole Centrale, Paris	Member
V. Moureau	Engineer - TURBOMECA, Bordes	Member
M. Van Guzen	Assistant professor - Technische Universiteit, Delft	Member
S. Roux	Engineer - SNECMA, Villaroche	Invited member
F. Nicoud	Professor - University of Montpellier II	Advisor