LASER BASED INVESTIGATIONS OF THERMO-ACOUSTIC INSTABILITIES IN A LEAN PREMIXED GAS TURBINE MODEL COMBUSTOR

摘要

Non-intrusive laser-based and optical measurements were performed in a gas turbine model combustor with a lean premixed swirl-stabilized CH_4-air flame at atmospheric pressure. The main objective was to gain spatially and temporally resolved experimental data to enable the validation of numerical CFD-results of oscillating flames. The investigated flame was operated at 25 kW and φ=0.70 and exhibited self-excited oscillations of more than 135 dB at about 300 Hz. The applied measurement techniques were 3-D LDV for velocity measurements, OH~* chemiluminescence yielding information about the heat release, and point-wise laser Raman scattering for the determination of joint PDFs of the major species concentrations, temperature, and mixture fraction. Each of these techniques was applied with phase resolution with respect to the periodic fluctuation of the pressure in the combustion chamber that was measured with a microphone probe. The measurements finally revealed that the mixing of fuel and air in this technical premixing system was strongly affected by the pressure fluctuations leading to changes in equivalence ratio during an oscillation cycle which in turn induced the pressure fluctuations.