Coupled interaction between unsteady flame dynamics and acoustic field in a turbulent combustor
TL;DR: A possible asymmetric bidirectional coupling between q ˙ ' and p ' is observed to exert a stronger influence on p ' than vice versa, and the directional property of the network measure, namely, cross transitivity is used to analyze the type of coupling existing between the acoustic field and the heat release rate fluctuations.
Abstract: Thermoacoustic instability is a result of the positive feedback between the acoustic pressure and the unsteady heat release rate fluctuations in a combustor. We apply the framework of the synchronization theory to study the coupled behavior of these oscillations during the transition to thermoacoustic instability in a turbulent bluff-body stabilized gas-fired combustor. Furthermore, we characterize this complex behavior using recurrence plots and recurrence networks. We mainly found that the correlation of probability of recurrence ( C P R), the joint probability of recurrence ( J P R), the determinism ( D E T), and the recurrence rate ( R R) of the joint recurrence matrix aid in detecting the synchronization transitions in this thermoacoustic system. We noticed that C P R and D E T can uncover the occurrence of phase synchronization state, whereas J P R and R R can be used as indices to identify the occurrence of generalized synchronization (GS) state in the system. We applied measures derived from joint and cross recurrence networks and observed that the joint recurrence network measures, transitivity ratio, and joint transitivity are useful to detect GS. Furthermore, we use the directional property of the network measure, namely, cross transitivity to analyze the type of coupling existing between the acoustic field ( p ′) and the heat release rate ( q ˙ ′) fluctuations. We discover a possible asymmetric bidirectional coupling between q ˙ ′ and p ′, wherein q ˙ ′ is observed to exert a stronger influence on p ′ than vice versa.Thermoacoustic instability is a result of the positive feedback between the acoustic pressure and the unsteady heat release rate fluctuations in a combustor. We apply the framework of the synchronization theory to study the coupled behavior of these oscillations during the transition to thermoacoustic instability in a turbulent bluff-body stabilized gas-fired combustor. Furthermore, we characterize this complex behavior using recurrence plots and recurrence networks. We mainly found that the correlation of probability of recurrence ( C P R), the joint probability of recurrence ( J P R), the determinism ( D E T), and the recurrence rate ( R R) of the joint recurrence matrix aid in detecting the synchronization transitions in this thermoacoustic system. We noticed that C P R and D E T can uncover the occurrence of phase synchronization state, whereas J P R and R R can be used as indices to identify the occurrence of generalized synchronization (GS) state in the system. We applied measures derive...
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TL;DR: In this article, the authors discuss various prognosis and mitigation strategies for thermo-acoustic instability based on complex system theory in turbulent combustors, where the authors view the thermoacoustic system in a turbulent combustor as a complex system and the dynamics exhibited by the system is perceived as emergent behaviors of this complex system.
Abstract: Thermoacoustic instability in turbulent combustors is a nonlinear phenomenon resulting from the interaction between acoustics, hydrodynamics, and the unsteady flame Over the years, there have been many attempts toward understanding, prognosis, and mitigation of thermoacoustic instabilities Traditionally, a linear framework has been used to study thermoacoustic instability In recent times, researchers have been focusing on the nonlinear dynamics related to the onset of thermoacoustic instability In this context, the thermoacoustic system in a turbulent combustor is viewed as a complex system, and the dynamics exhibited by the system is perceived as emergent behaviors of this complex system In this paper, we discuss these recent developments and their contributions toward the understanding of this complex phenomenon Furthermore, we discuss various prognosis and mitigation strategies for thermoacoustic instability based on complex system theory
88 citations
TL;DR: A feature space consisting of the principal component plane estimated from the probability distribution of the transition patterns, which is obtained by a support vector machine, allows the early detection of thermoacoustic combustion instability.
Abstract: Early detection of thermoacoustic instabilities is of interest to both applied physicists and engineers, to avoid resonance leading to self-destruction of gas-based engines and turbines. This study shows how a combination of complex-network physics and machine learning can be used to detect a precursor of thermoacoustic instabilities, which can help to prevent the onset of a potentially destructive combustion-driven instability.
66 citations
01 Jan 2021
TL;DR: In this article, a range of problems involving unsteady combustion such as thermoacoustic instability, flame blowout, fire propagation, reaction chemistry and flow flame interaction are discussed. But the focus is not on the effects of these processes on the actual combustion system.
Abstract: Reacting flow fields are often subject to unsteadiness due to flow, reaction, diffusion, and acoustics. Further, flames can also exhibit inherent unsteadiness caused by various intrinsic instabilities. Interaction between various unsteady processes across multiple scales often makes combustion dynamics complex. Characterizing such complex dynamics is essential to ensure the safe and reliable operation of high efficiency combustion systems. Tools from nonlinear dynamics and complex systems theory provide new perspectives to analyze and interpret the data from real systems. They could also provide new ways of monitoring and controlling combustion systems. We discuss recent advances in studying unsteady combustion dynamics using the tools from dynamical systems theory and complex systems theory. We cover a range of problems involving unsteady combustion such as thermoacoustic instability, flame blowout, fire propagation, reaction chemistry and flow flame interaction.
35 citations
TL;DR: The turbulence network, which consists of nodes and vertexes in weighted networks between vortices, can characterize the complex spatiotemporal structure of a flow field during thermoacoustic combustion instability.
Abstract: We numerically study the spatiotemporal dynamics and early detection of thermoacoustic combustion instability in a model rocket combustor using the theories of complex networks and synchronization. The turbulence network, which consists of nodes and vertexes in weighted networks between vortices, can characterize the complex spatiotemporal structure of a flow field during thermoacoustic combustion instability. The transfer entropy allows us to identify the driving region of thermoacoustic combustion instability. In addition to the order parameter, a phase parameter newly proposed in this study is useful for capturing the precursor of thermoacoustic combustion instability.
33 citations
TL;DR: This paper adopts tools from dynamical systems and complex systems theory to understand the dynamical transitions from a state of stable operation to thermoacoustic instability in a self-excited model multielement liquid rocket combustor based on an oxidizer rich staged combustion cycle.
Abstract: Liquid rockets are prone to large amplitude oscillations, commonly referred to as thermoacoustic instability. This phenomenon causes unavoidable developmental setbacks and poses a stern challenge to accomplish the mission objectives. Thermoacoustic instability arises due to the nonlinear interaction between the acoustic and the reactive flow subsystems in the combustion chamber. In this paper, we adopt tools from dynamical systems and complex systems theory to understand the dynamical transitions from a state of stable operation to thermoacoustic instability in a self-excited model multielement liquid rocket combustor based on an oxidizer rich staged combustion cycle. We observe that this transition to thermoacoustic instability occurs through a sequence of bursts of large amplitude periodic oscillations. Furthermore, we show that the acoustic pressure oscillations in the combustor pertain to different dynamical states. In contrast to a simple limit cycle oscillation, we show that the system dynamics switches between period-3 and period-4 oscillations during the state of thermoacoustic instability. We show several measures based on recurrence quantification analysis and multifractal theory, which can diagnose the dynamical transitions occurring in the system. We find that these measures are more robust than the existing measures in distinguishing the dynamical state of a rocket engine. Furthermore, these measures can be used to validate models and computational fluid dynamics simulations, aiming to characterize the performance and stability of rockets.
29 citations
References
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TL;DR: In this article, an experimental study of the mechanism of unstable combustion in a coaxial, optically accessible, bluff-body-stabilized dumpcombustor with natural gas and fuel was performed.
Abstract: Results from an experimental study of the mechanism of unstable combustion in a coaxial, optically accessible, bluff-body-stabilizeddumpcombustorwithnaturalgasasthefuelarereported.Aparametricstudywasperformed to investigate the effects of equivalence ratio, inletvelocity, inlet fuel distribution, inlet swirl, and centerbody recess oncombustionstability. It wasfoundthatall of theseparametershadan effectonthestability characteristicsofthis combustor.Atselectedunstableoperatingconditions,phase-resolvedCHchemiluminescenceimageswerecaptured to study the heat-release structure during one period of pressure oscillation. The e ame‐ e owe eld interaction that is depicted in these images indicates that e ame‐ vortex interactions, and the resultant e ame area changes, play a signie cant role in the instabilities that occur when there is no swirl. A simple analysis of these images, however, showedthate uctuatinge ameareaandequivalenceratioe uctuationsbothcontributetotheheatreleasee uctuations that drive the instability. Unstable combustion with swirl appears to be fundamentally different from unstable combustion without swirl in that instabilities with swirl occur near lean blowout and appear to be associated with repeated detaching and reattaching of the e ame from the centerbody.
206 citations
TL;DR: Active instability control (AIC) as mentioned in this paper uses external acoustic excitation by a loudspeaker to suppress the oscillations of a flame, where the excitation signal is provided by a microphone located upstream of the flame.
204 citations
TL;DR: In this article, a review explains why linear and nonlinear thermoacoustic behavior is so sensitive to parameters such as operating point, fuel composition, and injector geometry, and proposes tools to exploit this sensitivity in the future: adjoint-based sensitivity analysis to optimize passive control designs and complex systems theory to warn of impending thermo-acoustic oscillations and to identify the most sensitive elements of a thermo acoustic system.
Abstract: Nine decades of rocket engine and gas turbine development have shown that thermoacoustic oscillations are difficult to predict but can usually be eliminated with relatively small ad hoc design changes These changes can, however, be ruinously expensive to devise This review explains why linear and nonlinear thermoacoustic behavior is so sensitive to parameters such as operating point, fuel composition, and injector geometry It shows how nonperiodic behavior arises in experiments and simulations and discusses how fluctuations in thermoacoustic systems with turbulent reacting flow, which are usually filtered or averaged out as noise, can reveal useful information Finally, it proposes tools to exploit this sensitivity in the future: adjoint-based sensitivity analysis to optimize passive control designs and complex systems theory to warn of impending thermoacoustic oscillations and to identify the most sensitive elements of a thermoacoustic system
201 citations
01 Jan 1998
TL;DR: In this article, a comprehensive experimental study has been conducted on combustion instabilities in a premixed swirler injector system at various equivalence ratios, chamber pressures, and inlet air temperatures.
Abstract: A comprehensive experimental study has been conducted on combustion instabilities in a premixed swirler injector system at various equivalence ratios, chamber pressures, and inlet air temperatures. A stability map has been determined to indicate the range of operating conditions conductive to the occurrence of instabilities. The amplitude of instabilities was found to be a strong function of the equivalence ratio, with pressure oscillations as high as 20% of the mean chamber pressure and unsteady velocities comparable to the mean flow values observed for equivalence ratios around 0.6. On the other hand, beyond an initial threshold value of inlet air temperature at which instability suddenly initiated, variations in inlet air temperature had minimal effect on the strength of instabilities. Measurements of steady and unsteady flame structures carried out using CH chemiluminescence and photographic imaging techniques indicate that the onset of instabilities can potentially cause significant alterations in flame structure, sometimes even causing near extinction of the flame during certain periods of the oscillation cycle. Coupled longitudinal oscillations were observed in the combustion chamber and upstream duct. Instability characteristics such as frequency, mode shape, and phase obtained through pressure measurements were found to be in excellent agreement with predictions from a linear acoustic analysis. A strong correlation was found between the heat release and pressure fluctuations near the dump plane, indicating a possible mechanism for creating and sustaining instabilities.
201 citations