Influence of dampers on the damping rates of a lab scale annular combustor

The impact of dampers on the stability margin of an atmospheric lab-scale annular combustor is investigated experimentally. In this study, the number of dampers as well as their circumferential distribution is varied. The used acoustic damping devices are quarter wave tube resonators. Furthermore, a modeling approach based on linearized Euler equations is applied to analyze the effect of different resonator arrangements on the stability of the annular combustor numerically. Damping rates are extracted from dynamic pressure measurements in the combustion chamber that are used to evaluate the damping performance of different resonator arrangements. Two methods are employed for the data analysis. The first one uses Lorentzian fitting of the pressure spectra of the first azimuthal mode. The second method analyzes the autocorrelation of the acoustic pressure signals. Both methods rely on turbulent combustion noise measurements. Furthermore, the azimuthal pressure field is decomposed into two independent modes. This allows analyzing the unbalanced damping effect of spatially asymmetrical resonator distributions on both modes. We see that the circumferential placement of the dampers has a significant influence on the damping of the first azimuthal mode as both decomposed modes need to be damped sufficiently in order to obtain a more stable system. For this reason, it can be shown that with the same number of dampers different damping rates can be observed. The experimental findings are confirmed by a validated model of the annular combustor that is applied to numerically investigate and assess the influence of the considered resonator configurations on the modal dynamics of the first azimuthal mode.