Experimental investigation of the thermo-acoustic instabilities coupled with wall vibrations

In order to fulfil requirements regarding emission of harmful gases to atmosphere, the gas turbine technologies had to develop into clean techniques for energy generation. Lean premixed combustion of natural gas is one of them. Since during this process exceed of air is used, the total combustion temperature is relatively low. In consequence fewer pollutants are produced. The major drawback of this process is high sensitivity on the thermo-acoustic instabilities. Inside the combustion chamber interaction between several phenomena takes place. Three of them, i.e. combustion, acoustics and the combustion chamber walls vibration coupled together into closed feedback loop might finally lead to the gas turbine failure. The destruction process has an origin in flame intrinsic instabilities. When those are promoted by coupling the heat release fluctuations with acoustic field perturbations, the unsteady self-excited oscillations of the pressure field inside the combustion chamber grows up in the amplitude and exert significant forces on the chamber walls called liner. The liner is a critical component since has to operate reliably at extremely high temperatures. This has a significant negative influence on the liner performance and its material properties. Additional pressure forces acting on the walls surface due to unstable combustion reduce significantly the life time of the liner and gas turbine itself. In this paper the thermo-acoustic instabilities are investigated in combination with liner vibrations. The investigations are done at the combustion test rig which may operate with maximum power of 500kW and absolute pressure equal to 5bar. In order to observe influence of the wall configuration on the overall instabilities two liners constructions i.e. stiff and flexible one are taken into account. Both liners are investigated at various pressure levels. Finally, relation between perturbations upstream of the burner and system response in form of flame transfer function is obtained.