Impact of fuel supply driven instability on the response of hydrogen-enriched methane-air partially premixed turbulent flames

Abstract

Large eddy simulation (LES) for determining the flame transfer function (FTF) in a model gas turbine combustor is conducted to identify the cause of the dynamic flame response inside a combustor. Partially premixed flame with external forcing is considered for quantifying the impact of fuel feed system driven instability. At a forcing frequency of 50 Hz at the inlet of the fuel supply line, a sudden increase of the gain in both FTF and cold flow transfer function (CTF) is observed. Also, the flow instabilities in the vicinity of a swirler affecting the response of the fuel feed flow dynamics are observed. Furthermore, rotating vortices are generated at the inlets of a swirler, and appeared periodically, which dissipated later due to the influence of the turbulent characteristics of the fuel feed flow. These vortices block the fluid supply entering the swirler, resulting in the periodic injection into the combustor. The oscillation frequency of vortices at around 50 Hz coincides with the forcing frequency at which a strong flame response is shown, implying the influence of internal instabilities on the flame response. Also, the dynamic flame responses inside the combustor are studied where the swirling flame emerges. The flame shape is predominantly influenced by the inflow fluctuations entering the combustor, which induces the periodic flame-wall interactions and the flame length variations. The flame responses showed similar characteristics to the flow responses at the swirler outlet, indicating a strong influence on the fuel supply driven instabilities. Subsequently, the obtained FTF and CTF are validated against the experimental data for confirming the accuracy of the present LES results. Thus, the present findings have clarified the role of fuel supply driven instability on the swirling flame, which directly affects the FTF and combustion instability.