Numerical prediction of the Flame Describing Function and thermoacoustic limit cycle for a pressurised gas turbine combustor

ABSTRACT

The forced flame responses in a pressurized gas turbine combustor are predicted using numerical reacting flow simulations. Two incompressible¹ large eddy simulation solvers are used, applying two combustion models and two reaction schemes (4-step and 15-step) at two operating pressures (3 and 6 bar). Although the combustor flow field is little affected by these factors, the flame length and heat release rate are found to depend on combustion model, reaction scheme, and combustor pressure. The flame responses to an upstream velocity perturbation are used to construct the flame describing functions (FDFs). The FDFs exhibit smaller dependence on the combustion model and reaction chemistry than the flame shape and mean heat release rate. The FDFs are validated by predicting combustor thermoacoustic stability at 3 and 6 bar and, for the unstable 6 bar case, also by predicting the frequency and oscillation amplitude of the resulting limit cycle oscillation. All of these numerical predictions are in very good agreement with experimental measurements.

KEY WORDS:

• Thermoacoustic limit cycle
• pressurized combustor
• reaction chemistry
• incompressible LES
• flame describing function

Acknowledgments

Experimental data from DLR and financial support from Siemens Industrial Turbomachinery Ltd., ERC Starting Grant ACOULOMODE, EPSRC CDT in Fluid Dynamics across Scales and Department of Mechanical Engineering at Imperial College are all acknowledged. Access to HPC facilities at Imperial College and via the UK’s ARCHER are acknowledged. We also thank Dr Jim W. Rogerson and Dr Ghenadie Bulat from Siemens Industrial Turbomachinery Ltd. for their contributions.

Conflicts of interests

Authors Yu Xia, William P. Jones and Aimee S. Morgans have received funding from the Siemens Industrial Turbomachinery Ltd.

Notes

² Recent computations of laminar flames with BOFFIN using accurate transport properties reproduce the GRI results.

Additional information

Funding

This work was funded by the Siemens Industrial Turbomachinery Ltd., the EPSRC Centre for Doctoral Training (CDT) in “Fluid Dynamics across Scales”, the Department of Mechanical Engineering at Imperial College London, and the European Research Council (ERC) Starting Grant (grant No: 305410) ACOULOMODE (2013–2018).