Double period thermoacoustic oscillation in swirl stabilised flame
ORAL
Abstract
A partially-premixed swirl-stabilised CH4-Air flame is studied using Large Eddy Simulation (LES). LES is performed at a thermal load of Pth = 25kW and a global equivalence ratio of Φ = 0.9 using an unstrained flamelet model for sub-grid reaction rate. Simulation results show good agreement with PIV and Raman measurements for velocity, temperature and mixture fraction statistics. A self-excited thermoacoustic instability undergoing a period-2 limit cycle oscillation (LCO) at 314 Hz (f1) and 628 Hz (f2) is observed. The pressure amplitude of the LCO has a time-varying behaviour at f2. Time-evolution of the flame, flow fields and coherent structures are studied during the thermoacoustic cycle to reveal the feedback mechanism. The three-dimensional phase space representation of pressure shows a double-loop attractor. The heat release rate strongly couples with the first mode compared to the second mode resulting in a single-loop attractor. Rayleigh index based on the Rayleigh Criterion [2] is analysed to understand the stronger coupling of the heat release rate and pressure fluctuations at f1 compared to f2.
*A. D. Kumar acknowledges the financial support from the Cambridge Trust. The University of Cambridge authors acknowledge the support from Mitsubishi Heavy Industries, Ltd., Japan. This work used the ARCHER2 UK National Supercomputing Service(https://www.archer2.ac.uk). The authors are grateful to the EPSRC (grant number EP/R029369/1) and ARCHER2 for financial and computational support as a part of their funding to the UK Consortium on Turbulent Reacting Flows (https://www.ukctrf.com).
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Presenters
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Ankit D Dilip Kumar
- University of Cambridge, Department of Engineering