Combining a Helmholtz solver with the flame describing function to assess combustion instability in a premixed swirled combustor

Limit cycles of combustion instabilities can be estimated by studying the nonlinear behavior of flame dynamics. In the present study the flame describing function (FDF) framework is combined with a linear acoustic Helmholtz solver in order to estimate the growth rate of the acoustic perturbations in a swirled combustor. It is assumed that when this growth rate equals the inherent dissipation of the system, acoustic oscillation amplitudes cease to grow and a stationary state, i.e., a limit cycle, is reached. In the same way, the FDF is combined with an analytical acoustic model for a quasi-1D version of the combustor. Numerical and analytical results are compared to experimental data and a reasonable agreement is obtained in terms of frequency, growth rate and amplitude of oscillations at the limit cycle.