A Comprehensive Thermoacoustic Framework Based on Doak’s Momentum Potential Theory – Application to Combustion Noise of the VOLVO Test Rig from LES Data

Abstract An extension to multi-species and reacting flows of Doak’s “Momentum Potential Theory of Energy Flux carried by Momentum Fluctuations” is proposed as a general and comprehensive framework for thermoacoustic characterization of combustor systems. This framework is applied here for the first time in its extended form to analyze simulation data relative to the flow in a bluff-body stabilized combustor, in stable operating conditions. The proposed thermoacoustic model is able to: (i) unambiguously separate turbulent, acoustic, thermal, and mixture fluctuations; (ii) effectively describe the interaction between turbulent, acoustic, thermal, and mixture dynamics; (iii) highlight the main characteristics of the combustion noise emitted by the systems. By means of the performed analysis, the thermal phenomena are found to dominate the dynamics interaction. All convective quantities interact in the shear layer at the flame border and feature a similar, low-frequency spectral behavior. As expected, the acoustics does not couple directly with the convective quantities, due to the considered stable conditions. Although, the acoustic spectrum is strongly characterized by three peaks, which can be attributed to secondary, high-frequency thermal fluctuations. The modes related to these peaks can be seen, therefore, as a representation of the combustion noise emitted by the flame. The new terms related to the mixture do not seem to effectively contribute to the dynamics interaction and to the acoustic production, at least for the considered configuration and operating conditions.