Large eddy simulations of inlet temperature effects on the combustion instabilities in a partially premixed coaxial staged model combustor

Abstract

To investigate the effects of inlet temperature on the combustion instability in a partially premixed coaxial staged model combustor, the Wall-Modeled Large Eddy Simulations and Flamelet Generated Manifolds are conducted for the combustion field structure and dynamic combustion characteristics at different inlet temperatures. The results show that the increasement of the inlet temperature leads to an enlargement of the axial size of the primary recirculation zone. Meanwhile, there is stronger velocity pulsation near the shear layer, but the temperature and heat release rate pulsation intensity at the shear layer weaken. With the increase of the inlet temperature, the flame anchor position shifts upstream, moving up by 10 mm from case 1 to case 2. This is because as the inlet temperature increases, the flow velocity rises for the same mass flow rate, resulting in stronger swirl in the pilot-stage. Consequently, the flame root transitions from the stabilized with main-stage swirl to the stabilized with pilot-stage swirl. The results of Fast Fourier Transfer and Dynamic Mode Decomposition reveal that there are two primary modes in the combustor, with frequencies of approximately 430 Hz and 1100 Hz. The results of the low-order thermoacoustic network indicate that as the inlet temperature increases from case 1 to case 2, the growth rate of the 430 Hz mode decreases from 4.5 rad s^-1 to -9.4 rad s^-1. This is also consistent with the gain trend of the flame transfer function, where, as the inlet temperature increases, the low-frequency gain decreases.