Theoretical and numerical study of symmetry breaking effects on azimuthal thermoacoustic modes in annular combustors

Abstract

A large range of physical problems, from molecules to giant stars, contains rotating symmetry and can exhibit azimuthal waves or vibrations. When this symmetry is broken, the system can become unstable with chaotic behaviors. Symmetry breaking is investigated in annular combustors prone to azimuthal thermo-acoustic instabilities. First, theories reveal that two types of symmetry breaking exist : due to different burner types distributed along the chamber or due to the flow itself . It leads to frequency splitting, fixes the mode structure and can destabilize the configuration. A UQ analysis is also performed to quantify the symmetry breaking effect due to uncertainties of flame descriptions or behaviors. To complete theory, Large Eddy Simulations are performed on a single-sector as well as on a complete 360° configuration of the annular experiment of Cambridge. Numerical results are compared to experimental data showing a good agreement. In particular, an unstable azimuthal mode at 1800 Hz grows in both LES and experiment. However, LES cannot investigate the limit cycle because of its extreme cost. To tackle this problem, a new methodology is developed, called AMT, where theory or Helmholtz solver predictions are injected into LES or DNS. This method allows to study symmetry breaking, mode nature and dynamics as well as evaluating damping in realistic annular configurations