Nonlinear dynamics of a simplified subcritical thermoacoustic system under axial structure vibration

Energy conversion from heat to acoustics remains one of the major challenges in high-performance propulsion systems, due to the incurred serious threat to the structural safety of engine and the reliability of system operation. In this paper, the influence of axial structural vibration on the nonlinear dynamics of a subcritical thermoacoustic system are investigated using large eddy simulation and moving mesh techniques. Multiple analysis methods, including time series analysis, reconstructed phase portrait, spectrum analysis, and wavelet analysis are employed to analyze the system response. When the thermoacoustic system is configured in the globally stable region, the acoustic oscillations grow monotonically with the increase of structure vibration, and resonant conditions lead to more severe thermoacoustic oscillations compared to non-resonant cases. In the hysteresis region, the structure vibration can trigger the silent thermoacoustic system to exhibit intense oscillations, and the minimum vibration amplitude for the triggering is obtained at different operating condition. Under non-resonant conditions, low-frequency vibrations need lower amplitude to trigger than high-frequency vibrations. Once the system becomes unstable, external structural vibrations exert a modulating effect on the high-amplitude limit cycle oscillations. These findings offer valuable insights into the interplay between axial structural vibration and thermoacoustic instability in thermoacoustic systems.