Validation of a Physics-Based Low-Order Thermo-Acoustic Model of Combustion Driven Oscillations in a Liquid Fueled Gas Turbine Combustor

Validation test results of a low-order thermoacoustic model of combustion dynamics in a liquid-fueled, gas turbine combustor are presented. A finite element model designed in COMSOL Multiphysics is used as a tool for predicting naturally occurring combustion instabilities. The combustion rig consists of an inlet plenum, nozzle, combustor, and variable length transition tube. The combustor is run at pilot only mode at high pressure (up to 4 atm), resulting in sooty fuel-rich flame. The global flame transfer function is measured using flame emission at OH* band (307±5 nm) from the whole flame with inlet velocity fluctuation which is measured using multi-microphone measurement. The impedances at the choked inlet and exit of combustor are measured using a multi-microphone method, showing that the actual impedances of choked inlet and exit are different from theoretical values. Using the measured flame transfer function and impedances, the model’s capability to predict the instabilities is examined for two different rig configurations: one with a 10”-long transition tube and the other with a 20”-long transition tube. The modelling results are shown to converge to eigenfrequencies close to those measured experimentally. They correctly predict the stability regime of each of the tested conditions and frequencies of oscillations to within a maximum of 4% error. Using measured acoustic boundary conditions at the inlet and exit orifice improves the prediction of instability frequency.