Influence of pulsed air entries on a spray generated by an air-blast injection device : an experimental analysis on combustion instability process in aeroengines

Abstract

Recent advances in aeroengine design tend to diminish the thrust-to-weight ratio and to ameliorate the combustion efficiency, taking into account the optimization of both pollutant emissions and noise level. Due to higher pressure and temperature ranges in the combustion chamber, instability processes exerted by aero-acoustic-combustion couplings may appear occasionally. Although such phenomena occuring in turboengines have been investigated since the 1980s, theONERA Centre de Toulouse took the initiative to develop an experimental set-up in order to investigate the twophase flow issued from an air-blast atomizer driven by combustion instability processes, under non-reacting and reacting conditions. The modulation exerted by the acoustic pressure on the injection is experimentally simulated by pulsating the entries (air and fuel with specific actuators placed upstream of the injector). This paper presents a review of the spray characterization under non-reacting conditions and the first results obtained with combustion. The set-up and the measurement techniques developed in order to follow high-frequency phenomena involved in the spray are described first. Second, the dynamics of the pulse-swirled jet and the effect on the transported phase under non-reacting conditions are discussed.Free and confined jet configurations are compared. Third, the perspectives of the actual work are defined according to the observations in combustion.