Affiliation:
1. Department of Mechanical Engineering, College of Engineering, University of Canterbury, Christchurch 8041, New Zealand
2. School of Mechanical Engineering, Tongji University, Shanghai 201804, China
3. School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
Abstract
Reducing the footprint of greenhouse gases and nitrogen oxides (NOx) emissions from combustion systems means that they have been operating under lean or ultra-lean fuel–air premixed conditions. Under such conditions, self-excited large-amplitude pulsating thermoacoustic instabilities may occur, characterized by deafening combustion noises and even “violent” structural vibrations, which is, therefore, highly undesirable in practice. By conducting chemical reaction-thermodynamics-acoustics-swirling flow coupling investigations, we have numerically explored the generation and mitigation mechanisms of self-excited pulsating oscillations in a methane-fueled swirling combustor in the presence and absence of an outlet nozzle. Hence, a large-eddy simulation was performed on a fully three-dimensional compressible flow via an open-source platform, OpenFOAM. Furthermore, a thorough assessment was made to understand the fundamental physics of the interaction of the swirling flame, either constructively or destructively, to the acoustic pressure perturbations by examining the local Rayleigh criterion/index. A further explanation was made on implementing the outlet nozzle that can mitigate such periodic pulsating combustion via attenuating the fuel fraction fluctuations, vortices processing, and changing temperature field. It was also found that the dominant pulsating mode is switched from the 1/4 standing-wave wavelength mode to the 3/4 wavelength mode. Finally, more physical insights were obtained by conducting a proper orthogonal decomposition analysis on the energy distribution between the thermoacoustic modes.
Funder
College of Engineering, University of Canterbury
National Research Foundation Singapore
Ministry of Science and Technology of the People's Republic of China
Subject
Condensed Matter Physics,Fluid Flow and Transfer Processes,Mechanics of Materials,Computational Mechanics,Mechanical Engineering