Impact of transverse acoustic modes on a linearly arranged two-phase flow swirling flames

Abstract : The energy needs of population around the word are continuously increasing. For instance, forecasts indicates an important grow of the request of the aeronautic transportation sector. It is necessary to continue the research efforts to get more performants and less contaminating systems. New concepts for combustion have been developed and introduced to the gas turbine industry. Among these concepts it is found technologies based on lean-premixed combustion or lean-premixed prevaporized combustion when liquid fuels are employed. These novel energetic systems, making use of lean combustion, are promising to meet the future norms about pollutant emissions, but this make them more sensitive to combustion instabilities that limit their operating range and can lead to irreversible damage. In this domain, many questions still need to be considered. In particular that of the behavior of two-phase flow swirling flames subjected to acoustic perturbations. Indeed most of aero-engines operate with this type of flames, but the dynamics and mutual interaction of these flames, as they are submitted to acoustic perturbation, are not yet well understood. This work addresses these issues and gives some understanding elements for the mechanisms driving the response of the flow and of the flame to acoustic perturbations and delivers data to validate models predicting unstable operating points.The experimental bench employed for this work is TACC-Spray. It has been designed and developed in the CORIA laboratory during this PhD thesis which is inscribed in the framework of the ANR FASMIC project. The injections system that equips this bench is composed by three swirled injectors fed with a liquid fuel (here n-heptane), developed by the EM2C laboratory. They are linearly arranged in the bench such that this represents an unwrapped sector of an annular chamber. The setup, being new and complex, needed technical solutions developed during this work and applied then in order to equip TACC-Spray with pressure and temperature sensors, a photomultiplier as well as adequate optic diagnostics (LDA, PDA, high speed imaging systems). In this study, the energetic system, composed by the two-phase swirling flow and the spray flame, has been submitted to the impact of a transverse acoustic mode excited within the acoustic cavity. The system response has been studied as a function of its location in the acoustic field. Three basins of influence of the acoustic field on the energetic system have been chosen, namely: (i) the pressure antinode characterized mainly by strong pressure fluctuations, (ii) the intensity antinode where important acoustic pressure and velocity gradients are present, (iii) the velocity antinode with strong velocity fluctuations where the acoustic pressure is residual. The approach of the study presented here is to investigate in first place the energetic system free of acoustic forcing. The results concerning this first study are presented in the Part I of this manuscript. In second place, the energetic system is placed in each of the location of interest within the acoustic field and the response of the air flow without combustion, that of the two-phase flow with combustion and finally that of the spray flames, are systematically investigated. The results of the study under acoustic forcing are shown in Part II of the manuscript.
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Marcos Caceres. Impact of transverse acoustic modes on a linearly arranged two-phase flow swirling flames. Mechanical engineering [physics.class-ph]. Normandie Université, 2019. English. ⟨NNT : 2019NORMIR01⟩. ⟨tel-02296934⟩

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