Numerical Investigation of Combustion Instability in a V-Gutter Stabilized Combustor

Abstract

The stability of the combustion process in a V-gutter stabilized combustor is numerically investigated. To this end, 3D compressible turbulent and unsteady reacting flow calculations have been carried out using LES. The time history of the pressure at several locations is used to determine the frequency and amplitude of the oscillations along with the mode shapes. A shift in the dominant mode of the frequency spectra from the acoustic mode to the hydrodynamic mode is observed. A POD analysis of pressure time histories on the symmetry plane also corroborates this trend. The computational domain is divided into several subvolumes in the wake region of the V-gutter and the time histories of pressure, temperature, and heat release are collected in the individual volumes. It is seen that the fluctuation of pressure and heat release tend to oscillate from being in phase to out of phase over a time period. Unstable regions predicted by the Rayleigh index across a plane are shown to be different from those predicted in a volume owing to the three dimensionality of the flame. Quite interestingly, the calculated values of the indices show the combustor to be most unstable for an equivalence ratio of 0.1665 which is not the leanest one considered here. The global Rayleigh index is shown to correlate well with the amplitude of the dominant mode.