Étude expérimentale du rôle de la phase liquide dans les phénomènes d’instabilités thermo-acoustiques agissant au sein de turbomachines diphasiques

Other literature type French OPEN
Apeloig, Julien (2013)
  • Subject: Instabilités thermo-acoustiques. Écoulement diphasique. Injecteur aéronautique | Moyenne de phase | PLIF | 532 | Thermo-acoustic instabilities | Multiphase flow | Aeronautical injection system | Phased-average analysis

Le travail présenté concerne l'étude des instabilités thermo-acoustiques apparaissant dans une chambre de combustion aéronautique. Le montage expérimental permet de faire varier continument les fréquences de résonances et de passer pour une même condition d'écoulement, d'un régime de combustion stable à un régime instable. La caractérisation complète d'un cas instable comprend une mesure des conditions acoustiques aux limites du banc, une analyse du comportement des phases liquide et évaporée, de celui du dégagement de chaleur instationnaire et une mesure de la fonction de transfert de la flamme. Ces travaux ont mis en évidence trois phénomènes jouant sur l’injection cyclique de carburant liquide. Les temps caractéristiques des différents phénomènes intervenant dans le couplage thermo acoustique et une distribution spatiale de l'indice de Rayleigh sont présentés. The purpose of this experimental study was to further our understanding of the fuel spray behavior during combustion instability phenomena in combustion chambers. An aeronautical injection system with dual kerosene lines was mounted on the LOTAR setup, which was equipped with an adjustable exhaust length. Stability maps were generated by varying the global equivalent ratio and the fuel split parameter, for two Inner Exhaust Lengths (IEL). A non-unique multiphase flow condition was found to produce stable and unstable combustion for different IELs. Each configuration was fully characterized. Acoustic boundary conditions were measured using the 2-microphone technique. Different optical techniques were used to analyze the unsteady behavior of the liquid phase, fuel vapor, and heat release. Moreover, two techniques were exploited to study the Flame Transfer Function using velocity measurements upstream and downstream of the injection device. Altogether, these results highlighted three atomization phenomena occurring during the cycles of thermo-acoustic instabilities. The phase-averaged analysis applied on the different measurements permitted to determine the time scales associated with each process appearing in the thermo acoustic coupling. This cyclic injection of liquid fuel into the chamber was followed by a vapor phase increase corresponding to a wave of equivalent ratio. The delay between the two phenomena was of 10°. In addition, OH* emissions showed a cyclic behavior following these waves. The delay between the wave of equivalent ratio and the unsteady heat release was approximately of 25°. Finally, spatial distribution of the Rayleigh index revealed that the inner recirculation zone contributed to sustain the combustion instability.
Share - Bookmark