Experimental Study of Damper Position on Instabilities in an Annular Combustor

Abstract

The present study experimentally investigates the effects of different circumferential damper configurations on the instabilities in an annular combustor. The combustor consists of multiple bluff body swirl stabilized flames. It is operated with a ethylene-air premixture at a power of 66 kW. Combinations of Helmholtz resonators are used as dampers circumferentially arranged around the combustion chamber. The tests are performed at operating conditions where the combustor is self-excited and characterized by a strong standing mode and periodic mode switching. For each test, the dynamic pressure is measured at different locations and overhead imaging of OH* of the entire combustor is conducted simultaneously at a high sampling frequency. The measurements are then used to compare the pressure fluctuations of the different cases in order to find the best positioning of the dampers. The azimuthal modes in the chamber are determined and the phase shift between OH* and pressure is analysed. Based on the Rayleigh criterion, these investigations allow us to find out if the dampers only remove energy from the pressure oscillations, or if they also influence the instability margins of the combustor and the flame dynamics. Finally, the results are compared with the theoretical findings in literature and observed discrepancies are discussed.