Time resolved flowfield, flame structure and acoustic characterization of a staged multi-injection burner Se ´verine Barbosa * , Philippe Scouflaire, Se ´bastien Ducruix Laboratoire EM2C, C.N.R.S., Ecole Centrale Paris, Grande Voie des Vignes, 92295 Cha ˆtenay-Malabry, France Abstract The present work details the analysis of staging and multipoint injection effects on the flow field, flame structure and acoustic properties of a lean swirled injector, representative of a gas turbine burner. The study is carried out for a constant power and global equivalence ratio while the staging parameter a between pilot and multipoint stages is varied. Using PLIF-OH, it is shown that the flame structure consists in a large central recirculation zone of burnt gases surrounded by an annular conical jet of fresh gases. The OH spatial distribution indicates that increasing a significantly modifies the flame structure, which becomes more compact and more organized while the mean flame front angle increases. Using High Frequency PIV in the reactive situation, a temporal analysis of the velocity field is carried out, indicating that large coher- ent structures appear periodically within the combustion chamber. The structure frequencies are deter- mined and compared with acoustic measurements. This comparison indicates that for a = 0%, the vortex frequency is slightly lower than the first eigenmode of the chamber, while for a = 30%, it corre- sponds to a secondary peak at a higher frequency of the spectrum for both p 0 and q 0 , with dramatic con- sequences on the burner behavior in terms of stability. When a increases starting from zero, the level of p 0 and q 0 increases to reach a maximum value for a = 20% before decreasing for higher staging. This acoustic behavior can be compared with the evolution of the temperature in the injector, that also reaches a max- imum value for a = 20%, proving that strong instabilities are associated with flame stabilization within the injector. Increasing the staging factor makes it possible to decrease the flame instability level while keeping the flame compact and robust. Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Gas turbine; Multipoint injection; Flame dynamics; High frequency PIV; Acoustic flame interactions 1. Introduction Lean premixed combustion devices have been widely developed to reach low NO x level in indus- trial applications. However, in this combustion regime, strong instabilities may occur leading to mechanical damages or flame extinction [1,2]. At the design stage, several solutions have already been proposed to improve flame stabilization in the combustion chamber. First, swirled flows per- mit to enhance the combustion process by improving the mixing rate between fuel and oxi- dant streams and the flame stabilization itself through the swirl-induced recirculation of hot products near the nozzle [3]. Nevertheless, swirl- ing flames often feature large periodic coherent 1540-7489/$ - see front matter Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2008.06.139 * Corresponding author. Fax: +33 1 47 02 80 35. E-mail address: severine.barbosa@em2c.ecp.fr (S. Barbosa). Available online at www.sciencedirect.com Proceedings of the Combustion Institute 32 (2009) 2965–2972 www.elsevier.com/locate/proci Proceedings of the Combustion Institute