| 1. |
- Wildemans, Roeland, et al.
(författare)
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Nonlinear dynamics of pure intrinsic thermo-acoustic modes
- 2023
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 251, s. 112703-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the nonlinear dynamics of the pure Intrinsic Thermo-Acoustic (ITA) modes are experimentally investigated for burner stabilized premixed flames by decoupling them from the acoustic modes. Thereto, a setup is used with up- and downstream mufflers that provide close to anechoic boundary conditions. This enables the investigation of the self-excited oscillations of the flame, without the influences of acoustic reflections. An experimental bifurcation analysis is conducted to systematically investigate the different asym ptotic oscillatory states and their transitions. By increasing the upstream velocity, the flame looses stability through a supercritical Hopf bifurcation and reveals limit cycles with a single dominant frequency. For increasing upstream velocity, a low frequent mode appears, resulting in quasi-periodic oscillations. This regime is characterized by a beating phenomenon with simultaneous amplitude and frequency modulations. When the upstream velocity is even further increased, a period doubling bifurcation is observed. To our best knowledge, the experimental investigation of the nonlinear dynamical behavior of pure ITA modes and, in particular, the low frequency oscillation, has not been reported before, and it provides valuable insights towards developing accurate time-domain models of the nonlinear acoustic behavior of premixed flames. Finally, a phenomenological model of two coupled oscillators is introduced that is able to qualitatively reproduce all observed nonlinear oscillations of the flames.
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| 2. |
- Wildemans, Roeland, et al.
(författare)
-
Parameter estimation of two coupled oscillator model for pure intrinsic thermo-acoustic instability
- 2023
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Ingår i: Nonlinear dynamics. - : Springer Nature. - 0924-090X .- 1573-269X. ; 111:14, s. 12835-12853
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear phenomenological model of two coupled oscillators is proposed, which is able to describe the rich nonlinear behaviour stemming from an unstable pure intrinsic thermo-acoustic (ITA) mode of a simple combustion system. In an experimental bifurcation analysis of a pure ITA mode, it was observed that for increasing mean upstream velocity the flames loose stability through a supercritical Hopf bifurcation and subsequently exhibit limit cycle, quasi-periodic and period-2 limit cycle oscillations. The quasi-periodic oscillations were characterised by low frequent amplitude and frequency modulation. It is shown that a phenomenological model consisting of two coupled oscillators is able to reproduce qualitatively all the different experimentally observed regimes. This model consists of a nonlinear Van der Pol oscillator and a linear damped oscillator, which are nonlinearly coupled to each other. Furthermore, a parameter estimation of the model parameters is conducted, which reveals a good quantitative match between the model response and the experimental data. Hence, the presented phenomenological dynamical model accurately describes the nonlinear self-excited acoustic behaviour of premixed flames and provides a promising model structure for nonlinear time-domain flame models.
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| 3. |
- Wildemans, Roeland, et al.
(författare)
-
Parameter identification of two coupled oscillator model for pure intrinsic thermoacoustic instability
- 2022
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Ingår i: Internoise 2022. - : The Institute of Noise Control Engineering of the USA, Inc..
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Konferensbidrag (refereegranskat)abstract
- In this paper, a nonlinear phenomenological model of two coupled oscillators is presented, which is able to describe the rich nonlinear behaviour stemming from an unstable pure Intrinsic Thermo-Acoustic (ITA) mode of a simple combustion system. In a bifurcation analysis of a pure ITA mode, it was observed that for increasing mean upstream velocity the flames loose stability through a supercritical Hopf bifurcation and subsequently exhibit limit cycle, quasi-periodic and period-2 limit cycle oscillations. The quasi-periodic oscillations were characterized by low frequent amplitude and frequency modulation. It is shown that a phenomenological model consisting of two coupled oscillators is able to reproduce qualitatively all the different experimentally observed regimes. This model consists of a nonlinear Van der Pol oscillator and a linear mass-spring-damper oscillator, which are nonlinearly coupled to each other. Furthermore, a parameter identification of the model parameters is executed, which shows a good quantitative match between the model and the experimental data. Hence, the presented phenomenological dynamical model accurately describes the nonlinear self-excited acoustic behaviour of premixed flames.
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