École Nationale Supérieure de
Techniques Avancées

Abstract

In the development of aeronautical motors, two requirements must be taken into account : to get the best performances and to respect the polluants legislation. To decrease polluant emissions, Snecma uses lean combustion. As a consequence, new combustors have to deal with combustion instabilities but the methods used until now to study the behaviour of combustion chambers show their lack of precision. Large eddy simulation performed in research laboratories can predict these behaviours. To foretell combustion instabilities, Snecma chooses to industrialize the AVBP numerical code based on large eddy simulation developed by CERFACS (Toulouse). In this project, this code is used to understand if flow detachments observed after diffuser blades during experimental investigations can lead to combustion instabilities. The numerical simulations made are non reactive large eddy simulations. Various parts of the diffuser are studied to investigate the influence of numerical parameters on the results. The studied geometries become more and more complex to account for more accurate physical phenomena. An analysis of the mean flow and a temporal analysis are given. Flow detachments are observed in the part surrounded the flame tube. These perturbations can enter into the tube flame by the primary holes and can lead to combustion instabilities. The part surrounded the flame tube is then added. This configuration is not satisfying : the air must enter in the flame tube to reflect what happens actually. The first part of this document introduces the ecologic issues and the polluants formation into gas turbines to point out a direct consequence of Nox emission reduction : combustion instabilities. The second part gives details concerning the numerical code AVBP used to compute the large eddy simulations. The third part gives a methodology to compute large eddy simulations at Snecma. The last part presents the studied configurations and the results obtained.