Large-eddy simulations of self-excited thermoacoustic instability in a premixed swirling combustor with an outlet nozzle

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.

Analysis of separating acoustics from the thermoacoustic system of methane combustion based on Reynolds-averaged Navier-Stokes and linearized Navier-Stokes equations

“…LES was applied to a realistic gas turbine combustion chamber configuration to investigate the evaluation of the terms in the acoustic energy equation and the identification of the mechanism driving the oscillation. 8 Sun et al 9 used the LES method to explore the generation and mitigation mechanisms of self-excited pulsation oscillations in a methane-fueled swirl combustor with and without an exit nozzle. To overcome the high computational cost required for LES, non-stationary Reynolds-averaged Navier-Stokes (URANS) simulations are used to obtain results as close to LES as possible.…”

Experimental Studies on Suppression of Combustion Instability with the Addition of Helium

“…In the case of combustion instability, pressure fluctuation has negative impacts on the combustion system (Huang and Yang 2009). Combustion instability is a complex physicochemical process in which fluid, acoustics and combustion are coupled, and it is usually studied by experiment (Harvazinski et al 2015) and numerical simulation (Zhao et al 2019;Sun et al 2022). As for the mechanisms of combustion instability, the excitations have not yet been fully understood (Murayama and Gotoda 2019).…”

Numerical optimizing noise damping performances of Helmholtz resonators with a rigid baffle implemented at neck in presence of a grazing flow

“…10,11 Acoustic damping performances of Helmholtz resonators could be evaluated by conducting time-or frequency-domain simulations. [5][6][7]12 The governing equations are coupled nonlinear Navier-Stokes equations. The vorticity-involved damping physics of Helmholtz resonators are visualized by these simulations 12,13,15 or flow visualizations or laserinvolved experimental measurements.…”

“…Optimizing the resonator neck may increase or decrease the transmission losses by 5–15 dB over a wide frequency range. Wu et al 5 numerically investigated aeroacoustics damping performance of a Helmholtz resonator in the presence of a joint bias-grazing flow. They showed that when a joint bias-grazing flow is present, the effects of the cooling/bias flow may give rise to a transmission loss peak being reduced around 5 dB.…”