No abstract

No abstract

No abstract

Self-excited combustion instabilities in a high pressure, single-element, lean, premixed, natural gas (NG) dump-combustor are investigated. The combustor is designed for optical access and instrumented with high frequency pressure transducers at multiple axial locations. A parametric survey of operating conditions including inlet air temperature and equivalence ratio has been performed, resulting in a wide range of pressure fluctuation amplitudes (p′) of the mean chamber pressure (pCH). Two representative cases, flames A and B with p′/pCH=23% and p′/pCH=12%, respectively, both presenting self-excited instabilities at the fundamental longitudinal (1L) mode of the combustion chamber, are discussed to study the coupling mechanism between flame-vortex interactions and the acoustic field in the chamber. 10 kHz OH*-chemiluminescence imaging was performed to obtain a map of the global heat release distribution. Phase conditioned and Rayleigh index analysis as well as dynamic mode decomposition (DMD) is performed to highlight the contrasting mechanisms that lead to the two distinct instability regimes. Flame interactions with shear layer vortex structures downstream of the backward-facing step of the combustion chamber are found to augment the instability magnitude. Flame A engages strongly in this coupling, whereas flame B is less affected and establishes a lower amplitude limit cycle.

This paper presents high-fidelity simulations of fuel injection and atomization in a hybrid air-blast atomizer for realistic gas turbine engines. In particular, the fuel injection and atomization characteristics under lean-blowout conditions are considered which corresponds to a low liquid Weber number. A Volume-of-Fluid approach is combined with a Lagrangian particle framework to accurately simulate the fuel injection and atomization for the pilot pressure-swirl atomizer. The simulation results are compared to the experimental measurements from PDPA techniques. Good agreement is found for spray angle, droplet size and droplet velocities. However, the simulation predicts an early breakup compared to the experiments due to the stringent mesh resolution requirement under low liquid Weber number conditions.