ROLE OF TURBULENCE IN MODIFYING THE COHERENT HEAT RELEASE RESPONSE OF ACOUSTICALLY EXCITED ROD-STABILIZED FLAMES

Modern power generation gas turbine engines operate in primarily fuel-lean conditions in order to mitigate harmful emissions. Lean combustion systems, however, are susceptible to combustion instabilities, which arise from a resonant coupling between coherent oscillations in the unsteady heat release rate and the acoustic modes of the combustor. The occurrence of combustion instabilities can severely limit engine performance and operability. To design effective instability control mechanisms, it is critical to understand the response of flames to coherent fluctuations in the velocity and pressure fields of the flow. In addition to coherent oscillations, combustor flow fields also experience high levels of perturbations arising from turbulence, which can significantly alter the flow and flame dynamics. In this work, we study the coherent heat release response of a rod-stabilized flame subjected to longitudinal acoustic forcing at two levels of in-flow turbulence. We systematically vary the amplitude of acoustic excitation at two frequencies - the natural frequency of vortex shedding and its first harmonic – at both turbulence levels. Our results show that the amplitude of the coherent heat release response is strongly dependent on the turbulence intensity. Additionally, the impact of turbulence on the coherent heat release response is a function of the acoustic forcing frequency. These results provide insight into the interaction between coherent and turbulent motions in the flow and their impact on unsteady heat release oscillations in gas turbine combustors.