Kyu Tae Kim/Domenic Santavicca
The Journal of Mechanical Science and Technology, vol. 23, no. 12, pp.3436-3447, 2009

Abstract : The dynamic response of a turbulent premixed flame to acoustic velocity perturbations was experimentally determined in a swirl-stabilized lean-premixed gas turbine combustor. CH* chemiluminescence intensity and the twomicrophone method were used to measure heat release rates and inlet velocity fluctuations, respectively. Using the n-τ formulation, gain and phase of flame transfer functions were incorporated into an analytic thermoacoustic model to predict instability frequencies and modal structures. Self-excited instability measurements were performed to verify eigenfrequencies predicted by the thermoacoustic model. Instability frequency predicted by the model is supported by experimental results. Results show that the self-excited instability frequency of ~ 220 Hz results from the fact that the flames amplify flow perturbations with f = 150 ~ 250 Hz. The other instability frequency of ~ 350 Hz occurs because the whole combustion system has an eigenfrequency corresponding to the ¼-wave eigenmode of the mixing section.

Keyword : Combustion instabilities; Flame transfer function; Gas turbine; Lean premixed; Linear stability analysis