Papers by Jayesh Dhadphale
arXiv (Cornell University), Dec 19, 2023
Chaos, Apr 1, 2023
We report the occurrence of amplitude death (AD) of limit cycle oscillations in a bluff body stab... more We report the occurrence of amplitude death (AD) of limit cycle oscillations in a bluff body stabilized turbulent combustor through delayed acoustic self-feedback. Such feedback control is achieved by coupling the acoustic field of the combustor to itself through a single coupling tube attached near the anti-node position of the acoustic standing wave. We observe that the amplitude and dominant frequency of the limit cycle oscillations gradually decrease as the length of the coupling tube is increased. Complete suppression (AD) of these oscillations is observed when the length of the coupling tube is nearly 3/8 times the wavelength of the fundamental acoustic mode of the combustor. Meanwhile, as we approach this state of amplitude death, the dynamical behavior of acoustic pressure changes from the state of limit cycle oscillations to low-amplitude chaotic oscillations via intermittency. We also study the change in the nature of the coupling between the unsteady flame dynamics and the acoustic field as the length of the coupling tube is increased. We find that the temporal synchrony between these oscillations changes from the state of synchronized periodicity to desynchronized aperiodicity through intermittent synchronization. Furthermore, we reveal that the application of delayed acoustic self-feedback with optimum feedback parameters completely disrupts the positive feedback loop between hydrodynamic, acoustic, and heat release rate fluctuations present in the combustor during thermoacoustic instability, thus mitigating instability. We anticipate this method to be a viable and cost-effective option to mitigate thermoacoustic oscillations in turbulent combustion systems used in practical propulsion and power systems.
Chaos, Apr 1, 2023
der to suppress thermoacoustic instability, a positive feedback between the phase oscillators and... more der to suppress thermoacoustic instability, a positive feedback between the phase oscillators and the acoustic field is disrupted by increasing the swirler rotation rate. Therefore, we incorporate the effect of the acoustics and active swirler in the model, which plays a significant role in determining the flame response and hence, suppression of thermoacoustic instability. The model not only captures temporal dynamics but also reproduces the features of the spatio-temporal synchronization observed in the experiments. Finally, we show the relationship between the control parameter in the model and the experiments using a simple parameter estimation technique. I. INTRODUCTION Lean combustion systems are prone to thermoacoustic instability wherein high amplitude acoustic pressure oscillations occur due to positive feedback between the unsteady turbulent flame and the acoustic modes of the combustion chamber 1,2. These oscillations can result in disastrous consequences such
arXiv (Cornell University), Jan 5, 2022
der to suppress thermoacoustic instability, a positive feedback between the phase oscillators and... more der to suppress thermoacoustic instability, a positive feedback between the phase oscillators and the acoustic field is disrupted by increasing the swirler rotation rate. Therefore, we incorporate the effect of the acoustics and active swirler in the model, which plays a significant role in determining the flame response and hence, suppression of thermoacoustic instability. The model not only captures temporal dynamics but also reproduces the features of the spatio-temporal synchronization observed in the experiments. Finally, we show the relationship between the control parameter in the model and the experiments using a simple parameter estimation technique. I. INTRODUCTION Lean combustion systems are prone to thermoacoustic instability wherein high amplitude acoustic pressure oscillations occur due to positive feedback between the unsteady turbulent flame and the acoustic modes of the combustion chamber 1,2. These oscillations can result in disastrous consequences such
arXiv (Cornell University), Aug 24, 2022
Thermoacoustic instabilities observed in turbulent combustion systems have disastrous consequence... more Thermoacoustic instabilities observed in turbulent combustion systems have disastrous consequences and are notoriously challenging to model, predict and control. Here, we introduce a mean-field model of thermoacoustic transitions, where the nonlinear flame response is modeled as the amplitude weighted response of an ensemble of phase oscillators constrained to collectively evolve at the rhythm of acoustic fluctuations. Starting from the acoustic wave equation coupled with the phase oscillators, we derive the evolution equations for the amplitude and phase and obtain the limit cycle solution. We show that the model captures abrupt and continuous transition to thermoacoustic instability observed in disparate combustors. We obtain quantitative insights into the model by estimating the model parameters from the experimental data using parameter optimisation. Importantly, our approach provides an explanation of spatiotemporal synchronization and pattern-formation underlying the transition to thermoacoustic instability while encapsulating the statistical properties of desynchronization, chimeras, and global phase synchronization. We further show using the model that continuous and abrupt transitions to limit cycle oscillations in turbulent combustors corresponds to synchronization transitions of second-order and first-order, respectively, of the phase-field comprising the phase difference of pressure and heat release rate fluctuations. We then rationalise our findings in terms of the frequency distribution of oscillators obtained from experiments. The present formulation provides a highly interpretable model of thermoacoustic transitions: changes in empirical bifurcation parameters which lead to limit cycle oscillations amounts to an increase in the coupling strength of the phase oscillators, promoting global phase synchronization. The generality of the model in capturing different types of transitions and states of pattern-formation highlights the possibility of extending the present model to a broad range of fluid-dynamical phenomena beyond thermoacoustics.
Chaos: An Interdisciplinary Journal of Nonlinear Science
We report the occurrence of amplitude death (AD) of limit cycle oscillations in a bluff body stab... more We report the occurrence of amplitude death (AD) of limit cycle oscillations in a bluff body stabilized turbulent combustor through delayed acoustic self-feedback. Such feedback control is achieved by coupling the acoustic field of the combustor to itself through a single coupling tube attached near the anti-node position of the acoustic standing wave. We observe that the amplitude and dominant frequency of the limit cycle oscillations gradually decrease as the length of the coupling tube is increased. Complete suppression (AD) of these oscillations is observed when the length of the coupling tube is nearly [Formula: see text] times the wavelength of the fundamental acoustic mode of the combustor. Meanwhile, as we approach this state of amplitude death, the dynamical behavior of acoustic pressure changes from the state of limit cycle oscillations to low-amplitude chaotic oscillations via intermittency. We also study the change in the nature of the coupling between the unsteady flame...
Cornell University - arXiv, Aug 24, 2022
Thermoacoustic instabilities observed in turbulent combustion systems have disastrous consequence... more Thermoacoustic instabilities observed in turbulent combustion systems have disastrous consequences and are notoriously challenging to model, predict and control. Here, we introduce a mean-field model of thermoacoustic transitions, where the nonlinear flame response is modeled as the amplitude weighted response of an ensemble of phase oscillators constrained to collectively evolve at the rhythm of acoustic fluctuations. Starting from the acoustic wave equation coupled with the phase oscillators, we derive the evolution equations for the amplitude and phase and obtain the limit cycle solution. We show that the model captures abrupt and continuous transition to thermoacoustic instability observed in disparate combustors. We obtain quantitative insights into the model by estimating the model parameters from the experimental data using parameter optimisation. Importantly, our approach provides an explanation of spatiotemporal synchronization and pattern-formation underlying the transition to thermoacoustic instability while encapsulating the statistical properties of desynchronization, chimeras, and global phase synchronization. We further show using the model that continuous and abrupt transitions to limit cycle oscillations in turbulent combustors corresponds to synchronization transitions of second-order and first-order, respectively, of the phase-field comprising the phase difference of pressure and heat release rate fluctuations. We then rationalise our findings in terms of the frequency distribution of oscillators obtained from experiments. The present formulation provides a highly interpretable model of thermoacoustic transitions: changes in empirical bifurcation parameters which lead to limit cycle oscillations amounts to an increase in the coupling strength of the phase oscillators, promoting global phase synchronization. The generality of the model in capturing different types of transitions and states of pattern-formation highlights the possibility of extending the present model to a broad range of fluid-dynamical phenomena beyond thermoacoustics.
In this paper, we report the first observation of complete mitigation of thermoacoustic instabili... more In this paper, we report the first observation of complete mitigation of thermoacoustic instability in a bluff-body stabilized turbulent combustor through the method of self-coupling. Self-coupling is achieved by coupling the acoustic field of the combustor to itself through a coupling tube. We characterize the effects of such acoustic self-feedback on the thermoacoustic instability of the system by varying the length and diameter of the coupling tube. We observe that the amplitude and the dominant frequency of the acoustic pressure fluctuations gradually decrease as the length of the coupling tube is increased. A complete suppression of thermoacoustic instability is observed when the coupling tube length is nearly 1.5 times the combustor length. Meanwhile, as we approach the suppression of thermoacoustic instability, the dynamical behavior of acoustic pressure changes from the state of limit cycle oscillations to low amplitude aperiodic oscillations via intermittency. We also study...
Open-loop control is known to be an effective strategy for controlling self-excited thermoacousti... more Open-loop control is known to be an effective strategy for controlling self-excited thermoacoustic oscillations in turbulent combustors. In this study, we investigate the suppression of thermoacoustic instability in a lean premixed, laboratory-scale combustor using experiments and analysis. Starting with a self-excited thermoacoustic instability in the combustor, we find that a progressive increase in the swirler rotation rate transitions the system from thermoacoustic instability to the suppressed state through a state of intermittency. To model such transition while also quantifying the underlying synchronization characteristics, we extend the model of Dutta et al. [Phys. Rev. E 99, 032215 (2019)] by introducing a feedback between the ensemble of mean-field phase oscillators and the basis expansion of the acoustic pressure governing equation. The assumption that coupling strength among the oscillators is a linear combination of acoustic and swirler rotation frequency is justified ...
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Papers by Jayesh Dhadphale