Thermo-acoustic instability can be caused by the feedback mechanism between unsteady
heat release, acoustic oscillations and flow perturbations. In a gas turbine combustor
limit cycles of pressure oscillations at elevated temperatures generated by the unstable combustion
process enhance the structural vibration levels of the combustor. In this paper, the
behavior of turbulent partially premixed flames in a laboratory-scale lean partially premixed
combustor (called as LIMOUSINE combustor) operating on natural gas- methane fuel mixtures
is studied by using CFD methods. Depending on the operating conditions, the flame
shows a stable or an unstable behavior. In order to predict the frequency and magnitude of
the thermo-acoustic instability, and also to capture the reacting flow physics within the combustor,
the influence of operating conditions on combustion characteristics is examined by
using unsteady three-dimensional RANS solution of the conservation equations. To understand
the effects of operating conditions on the observed stability characteristics, the time averaged
velocity fields were measured with Particle Image Velocimetry (PIV) for the thermoacoustically
stable and unstable operating conditions of the combustor. The comparison of
the CFD calculations with the mean velocity fields shows good agreement. The results of
the present study demonstrate the relationship between the flame structure, the mean velocity
filed and pressure fluctuations under different operating conditions
