Experimental Investigation and Numerical Prediction of Thermo-acoustic Instabilities and Associated Liner Vibrations Induced by Combustion Process in Gas Turbines

In this paper, lean premixed combustion on natural gas is studied in experimental and numerical way. Experiments are done at the state-of-the-art 500 kW thermal power combustion setup. The test rig resembles combustion chamber of gas turbine and can be pressurised up to 5 bar absolute pressure. The experimental study are applied for validation of numerical computations. For numerical calculations a hybrid approach combining CFD and FEM methods is used. Mutual interaction between acoustic wave propagation inside the combustion chamber and structural vibrations is studied applying acousto-elastic model. During the CFD computations, pressure fluctuations created by the flame in the combustion chamber, are calculated first. The results of the CFD are exported then to the FEM code, where interaction between acoustic waves and wall vibrations is resolved. To reduce the effect of numerical dispersion and dissipation of acoustic waves in the CFD code, only the pressure recorded near the flame region is transferred. To simulate acoustic waves next to the vibrating liner, the investigated model is equipped with acoustic elements designed to recognize a structure on one side and a fluid on the other side of the element. The frequencies at which thermo-acoustic instabilities may appear at given operational conditions are predicted. Furthermore, a modal analysis to mark the hazardous structural, acoustic and coupled modes and eigenfrequencies is performed. Computational results are validated against experimental data. Results are in good agreement.