Identification, Modeling and Control of Nonlinear Thermoacoustic Instability

• Applicant: Professorin Dr. Lipika Kabiraj
• Subject Area: Fluid Mechanics
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 248884514

• Final Report Year: 2020

Final Report Abstract

Thermoacoustic instability is a major issue for existing technical combustion systems and in the development of cleaner, more flexible future combustor technology. Among the less understood aspects of this instability is the dynamics of the coupled system (primarily involving the combustion chamber acoustics, and fluctuations in the flame) at fluctuations large enough such that linear approximations do not hold. Universal aspects of nonlinear systems, such as bifurcations, aperiodic oscillations, and chaos; are features that affect all practical combustion systems and their dynamics; but were identified only recently as the inherent noise in the system is always masking characteristic features and conventional analysis methodology cannot distinguish noise from nonlinear behavior. Moreover, noise itself affects the nonlinear coupling. Identifying nonlinear dynamics is critical for understanding the physics of the coupling phenomenon, and in particular for understanding the mechanisms through which the flame interacts to acoustics of the combustor. This understanding in turn is critical for developing stable systems and for controlling/supressing instability. The present project was undertaken to investigate the nonlinear dynamics of thermoacoustic instability, its implications on control, and to identify strategies for the control of nonlinear oscillations. The project involved detailed experiments on a model thermoacoustic rig driven by a 1W flat flame and with provisions for the control of inherent noise in the combustor, acoustic control of oscillations, measurements of the acoustic field and flame fluctuations, and fine control of a critical system parameter: the fuel-air ratio. Several new findings on nonlinear behavior of thermoacoustic systems were identified in this project: bifurcations and their relation to flame dynamics, the influence of external periodic forcing and noise to the system, and a more accurate control strategy for thermoacoustic system (but also applicable to other nonlinear systems). In particular, the identification of the effects of noise may be considered as a major development in the field. Coherence resonance, and P-bifurcations not only provide a better understanding to how thermoacoustic coupling—specifically the bifurcation to instability–is affected by the presence of inherent noise of varying amplitudes or the presence of a constant intensity noise in the presence of small variation in the operating conditions; but the findings also imply that the state-of-the-art estimation of deterministic features such as the system growth rate and its proximity to stability borders (boundaries of the operating envelope) are inaccurate and must be revised. The PI is investigating this specific aspect presently. The methods developed during the project were also found to be applicable for the study of other complex combustion-related phenomena. Specifically, transient events affecting such as flame flashback and blowout and noise-generation from turbulent flames were investigated in the project.

Publications

• Chaos in an Imperfectly Premixed Model Combustor, Chaos, Vol. 25, 2015, pp. 023101
  Kabiraj, L., Saurabh, A., Karimi, N., Sailor, A., Mastorakos, E., Dowling, A. P., and Paschereit, C. O.
  
• Coherence resonance in a thermoacoustic system, Phys. Rev. E, Vol. 92, No. 4, oct 2015, pp. 042909
  Kabiraj, L., Steinert, R., Saurabh, A., and Paschereit, C. O.
  
• Characterizing the signature of flame flashback precursor through recurrence analysis, Chaos: An Interdisciplinary Journal of Nonlinear Science, Vol. 26, No. 1, Jan. 2016, pp. 013110
  Christodoulou, L., Kabiraj, L., Saurabh, A., and Karimi, N.
  
• Effect of Noise on a Model Thermoacoustic System at its Stability Boundary, Springer Fachmedien Wiesbaden, 2016
  Steinert, R.
  
• Effect of phase-shift feedback on thermoacoustic coupling, IFAC-PapersOnLine, Vol. 49, No. 10, 2016, pp. 65–70
  Morán, B. M., Saurabh, A., Paschereit, C., and Kabiraj, L.
  
• Numerical results on noise-induced dynamics in the subthreshold regime for thermoacoustic systems, Journal of Sound and Vibration, Vol. 390, March 2017, pp. 55–66
  Gupta, V., Saurabh, A., Paschereit, C. O., and Kabiraj, L.
  
• On the nonlinear dynamics of convective-diffusive-reactive waves, Ph.D. thesis, University of Glasgow, School of Engineering, 2018
  Christodoulou, L.
  
• Phase-shift feedback control of nonlinear thermoacoustic oscillations, 25th International Congress on Sound and Vibration, Hiroshima, Japan, 2018, pp. 1–8
  Saurabh, A., Ehlert, A., Paschereit, C. O., and Kabiraj, L.
  
• Method for controlling a combustion apparatus and control device, European Patent Office, No. EP3450848, 2019
  Saurabh, A., Kabiraj, L., and Paschereit, C. O.