Numerical and experimental studies on self sustained thermo-acoustic combustion instabilities of an experimental rig for full-scale industrial burners

In this work a three-dimensional finite element (FEM) code is used to perform the stability analysis of an experimental rig designed and operated in order to study the propensity of full-scale industrial burners to thermo-acoustic combustion instabilities. The Burner Transfer Matrix (BTM) approach is used to characterize the influence of the burner. An experimental transfer matrix is used and compared with an analytical model. In the combustion chamber, the influence of the three - dimensional spatial distribution of the thermodynamics quantities in presence of the flame is considered. Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations are used to compute the base flow. A linear stability analysis of the entire system is performed considering the coupling between pressure oscillations (p′) and heat release fluctuations (q′) with a distributed n-τ linear Flame Transfer Function (FTF). A three-dimensional spatial distribution of time delay (τ) is reconstructed assuming the delay due to convection as the predominant effect. Under these assumptions a good agreement between numerical and experimental results is found both in terms of thermo-acoustic resonant frequencies and mode shape of the resonant modes for different setups of the analyzed system.