A 2D low-order thermoacoustic network model of annular combustor with baffles in the plenum

Experimental results showed that configuring different baffles (a regular baffle, a single- or double-layer perforated plate and a Helmholtz resonator) in the plenum has an impact on the self-excited oscillation in annular combustor. In this paper, a 2D low-order network model is proposed to describe this phenomenon and predict the modal frequencies and growth rates of longitudinal and circumferential thermoacoustic modes for annular combustor with different baffles. In the plenum, only the circumferential acoustic propagation and the influence of baffles on it are accounted for as the longitudinal geometry size is much smaller than the acoustic wavelength of the longitudinal mode. Pure longitudinal acoustic propagation is considered in burners and both longitudinal and circumferential ones are accounted for in the combustion chamber. These three modules are connected by jump conditions. Compared with the experimental results, Baffles using Helmholtz resonators feature the best damping performance for specific modes. The circumferential mode is converted to two unfolded non-degenerate modes when configuring perforated plates baffles. And these two modes are orthogonal to each other.