Analysis of Thermo-Acoustic Properties of Combustors and Afterburners

Abstract

Predicting thermo-acoustic instabilities in combustion chambers remains an important issue. These instabilities mainly contain hydrodynamic and acoustic waves and can lead to severe structural damage if the energy feedback due to combustion builds up high amplitudes. In order to predict their behavior, linearized flow solvers have been developed in combination with an Arnoldi extraction method to compute several of the least damped eigenmodes of combustor flows. This technique has been validated against an atmospheric combustor test rig, named Validation Rig I, in which both low frequency buzz and high frequency screech modes could be induced. Both types of modes have also been found computationally, by matching frequencies and modes shapes. A post-processing mode stability analysis procedure has also been developed with which any computed eigenmode may be analyzed with respect to the Rayleigh criterion. The results of the mode stability analysis are consistent with the corresponding unsteady RANS simulations, but not with the experimental data. Understanding the modes coupled with combustion can provide useful knowledge regarding the the possibility to suppress them.