Impact of damper placement on the stability margin of an annular combustor test rig

In the presented study a lab scale lean-premixed annular combustor comprising different axial and azimuthal patterns of dampers as well as several symmetrical and unsymmetrical damper placement patterns is investigated in five steps: In the first step the number of the dampers is increased considering only optimal distributions obtained from literature. As a result a nearly linear increase of damping with the number of dampers is observed. Second, other damper patterns are examined, which perform worse than the ideal distributions. It can be seen that a mode split can lead to differing damping rates of the two decomposed modes. In the worst case one of the modes isn’t damped any stronger than in the baseline measurement without any dampers. A number of selected representative circumferential damper patterns is investigated at two axial locations. It is generally observed that the axial position has an influence on damper performance as the upstream configurations with dampers in the flame region perform better than the downstream configurations. Using an optimum configuration with four dampers equally distributed around the circumference the increase of the window of operation of the annular combustor test rig in terms of equivalence ratio and thermal power is demonstrated. The azimuthal distribution of the dynamic pressure amplitude of the annular combustor test rig is determined and compared with the local damping rate. A correlation can be found which reveals that already very moderate damping rates lead to very low dynamic pressure amplitudes.