DYNAMICS OF THE BLUFF BODY STABILIZED FLAME IN A MODEL COMBUSTOR USING CFD

The onset of self excited thermo-acoustic instability in premixed combustion is currently a major research target. The turbulent fluctuations in the flame act as a sound source, producing a sound field inside the combustor and in the burner, upstream of the flame. This sound field if further amplified by turbulence, heat or other acoustic source may lead to a thermo-acoustic feedback. In the present study computational fluid dynamic analysis has been done on a model combustor (Rijke tube) with a bluff body injector, using a commercial software package (ANSYS CFX). Transient combustion calculations have been performed using the URANS k - omega model for turbulence and the TFC model for combustion of methane and air. The transient data is post processed by performing FFT and spectral analysis to reveal the dominant frequency that may lead to thermo-acoustic instability. The preliminary results suggest that the combustor shows coherent oscillations in the pressure at a frequency of about 80Hz. This frequency is also confirmed from the Strouhal number calculations, which are in line with the earlier observations. It is found that strong vortex shedding is the main source of instability in this type of burner-flame configuration.