60009 - Thermoacoustic Instabilities of Hydrogen-Enriched Partially Premixed Flames in a Swirl Combustor 

Large eddy simulations (LES) of premixed hydrogen-enriched swirling flames in a model gas turbine combustor (PRECCINSTA) were performed to investigate the flame topology and combustion instabilities. A novel compressible LES approach is utilised to account for the self-excited combustion dynamics. A transported probability density function (pdf) approach is adopted to account for sub-grid scale (sgs) turbulence-chemistry interaction, and the solution to the joint sgs-pdf evolution equation of the scalars is obtained by the stochastic field method. The chemistry is represented using a reduced chemical reaction mechanism containing 15 reaction steps and 19 species.

Various operating conditions are studied, with hydrogen volume fraction up to 40%. The results revealed that as the concentration of hydrogen increases, the flame is shortened in the longitudinal direction and more confined in the cross-sectional direction, which is consistent with experimental observations and is likely due to the corresponding increased flame speed. The self-excited limit-cycle oscillations for all considered conditions were successfully reproduced, with the predicted dominant frequencies of the chamber pressure spectra in good agreement with the measured values. Hydrogen addition is found to increased the dominant frequency significantly, which results in a different thermoacoustic behaviour of the flame. The feedback loop of the oscillations in the combustion is successfully captured and analysed with the temporal evolution of axial velocity and heat release presented.