PhD defense - S. Roux

Influence of air/fuel mixture modelling and computational domain
in Large Eddy Simulation of combustion instabilities.
Application to aeronautical burners.

(Confidential)

Delivered by INP Toulouse
Speciality: Fluid dynamics

June 21, 2007 - CERFACS

Pollutants legislation strengthen, especially for NOx emissions. The demand from industries towards aeronautical motor and industrial gas turbine performances are even more strict. As a consequence, new combustors have to deal with combustion instabilities and the methods used until now to study the behaviour of combustion chambers show their lack of precision like RANS or are too expensive and too slow to set up like experimental investigations. Large eddy simulation appears in this field like a fortunate tool to tackle the combustion instability phenomena. In this document is demonstrated the capacity of large eddy simulation to predict in details the mean flow as well as the unsteady behaviour of an ”academic” combustion chamber when it is used with an additional acoustic analysis tool. These simulations realized with the AVBP numerical code developed by CERFACS is validated by a large amount of experimental measurements done at DLR-Stuttgart and is part of the European program called PRECCINSTA. Besides, this thesis sheds light on the influence of taking into account or not the high pressure stator at the exit of the combustion chamber into the simulation domain in the case of a real aeronautic combustor. The main point of this work lies in the answers as well as in the questions that it gives concerning the boundary conditions that should be used in a good combustion chamber simulation.

The first part of this document introduces the ecologic issue and the pollutants into gas turbines to point out a direct consequence of NOx emissions reduction : combustion instabilities. The second part gives details concerning the numerical code AVBP used to compute the large eddy simulation of two configurations. The first of these two configurations consists in an ”academic” combustion chamber plugged on burner and is the third part of this document. The second configuration is a real aeronautic combustor and it is the fourth and last part of this thesis.