Investigation on thermo-acoustical instabilities related to a confined swirling burner

Abstract

Swirling lean nonpremixed flames are used in modern combustors. These flames are susceptible of ther-mo-acoustic combustion instabilities, caused by the cou-pling between heat release fluctuations and combustor acoustics. Thermo-acoustic instabilities are dynamic phe-nomena that represent a major threat for most modern combustion systems. It consists of the coupling and auto-sustenance of large amplitude and low frequency pressure and heat release oscillations. Analysis of thermo-acoustic combustion instabilities of a nonpremixed swirling flame is presented extensively in this paper. This study is concerned with the evaluation of the influences induced by the equivalence ratio on the thermo-acoustic combustion in-stabilities, as well with a numerical method for determin-ing these instabilities. This analysis is made by acoustic correlation between numerical simulation using the 3D RNG k-ε model and experimental results. The dominant frequencies are located in the ranges 20-50 Hz for the non-reactive flow, and 40-300 Hz for the reactive flow. Multi-ple acoustic sensors are used in the experimental setup in order to account for spectral acquisition and to help elimi-nate the irrelevant environmental noise.