Novel perspectives on the dynamics of premixed flames

Blumenthal, Ralf; Subramanian, Priya; Sujith, R. I.; Polifke, Wolfgang

doi:10.1016/j.combustflame.2013.02.005

Cited by 52 publications

(60 citation statements)

References 25 publications

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“…32,[43][44][45] It has been reported that this low-order model is capable of reproducing fairly realistic flame behavior observed for laminar wedge flames in both the linear 46 and nonlinear regime. 47 However, in general, the formulation of _ q in equation (17) allows for any linear filter deduced from experiments or numerical simulations.…”

Section: The Flame Subsystemmentioning

confidence: 99%

“…The dynamics of the acoustics/flow subsystem is approximated by a method of weighted residuals (MWR), which may be more familiar to the reader as Galerkin method. The dynamics of the flame subsystem is modeled by an impulse response filter model derived in Blumenthal et al 32 Since the output is a matter of choice, we decide to measure the dynamics of the model by defining the output energy to correspond to the acoustic energy with mean flow (sometimes referred to as Cantrell and Hart norm 33 ). In this case, the output only contains contributions from the states of the acoustics subsystem, and the output energy defines a semi-norm.…”

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confidence: 99%

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A systems perspective on non-normality in low-order thermoacoustic models: Full norms, semi-norms and transient growth

Blumenthal

Tangirala

Sujith

et al. 2016

International Journal of Spray and Combustion Dynamics

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Non-normal transient growth of energy is a feature encountered in many physical systems. Its observation is intimately related to the norm used to describe the system dynamics. For a multi-physics problem such as thermoacoustics, where a heat source is in feedback with acoustic waves and a flow field, the appropriate metric is an ongoing matter of debate. Adopting a systemic perspective, it is argued in the present paper that an energy norm is, in principle, a matter of choice, but one that is critically tied to the dynamics described by the system model. To illustrate our arguments, it is shown that different norms exhibit the non-normal dynamics of thermoacoustic systems differently, but that this difference is fully explicable by the energy flux and source terms related to the formulation of the model. The non-normal dynamics as such is unaffected by the choice of norm, and transient growth merely results from a maximization of the flux and source terms governing the energy balance associated with the specific model formulation. Investigating transient growth for arbitrary energy norms requires the capability to handle semi-norm optimization problems. In the present study, we propose an approach to do so using the singular value decomposition. Non-normal transient growth around a stable fix point is then investigated for a low-order model of a simple thermoacoustic configuration of a premixed flame enclosed in a duct with non-zero mean temperature jump and bulk mean flow. The corresponding optimal mode shapes and pertinent parameters leading to transient growth are identified and discussed. For transient growth resulting from the interaction of the flame with the acoustic field, it is found that heat sources with a fast response lead to more transient growth than slow heat sources, because the system can bear a larger source term before becoming linearly unstable. Furthermore, the amount of transient energy growth does not increase monotonically with the amplitude of the initial perturbation of the flame.

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Section: The Flame Subsystemmentioning

confidence: 99%

mentioning

confidence: 99%

A systems perspective on non-normality in low-order thermoacoustic models: Full norms, semi-norms and transient growth

Blumenthal

Tangirala

Sujith

et al. 2016

International Journal of Spray and Combustion Dynamics

Self Cite

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“…Kinematic Over-Restoration subsequently takes place. Standard kinematic restoration happens when a flame, pushed away from its stable position, naturally reverts to steady state [42,43]. Here, not only is the flame far from its equilibrium position at t = t 3 , but the inlet velocity is also minimal at this instant: these two combined factors lead to a very fast contraction of the flame between instants t 3 and t 4 .…”

Section: Description Of Physical Phenomena Responsible For Ita Modesmentioning

confidence: 99%

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Courtine

Selle

Poinsot

2015

Combustion and Flame

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. , Emmert et al. 2015 suggest that thermoacoustic modes can appear in combustors with anechoic terminations, which have no acoustic eigenmodes. These modes, called here Intrinsic ThermoAcoustic (ITA), can be predicted with simple theoretical arguments, but have been ignored for a long time. They are reproduced in this paper using Direct Numerical Simulation (DNS) of a laminar premixed Bunsen type flame. DNS results and theory are compared showing very good agreement in terms of both frequency and mode structure. DNS confirms that the frequency of ITA modes does not depend on any acoustic characteristic of the burner. Based on a numerical evaluation of the Flame Transfer Function, stability limits of ITA modes predicted by theory are also recovered in the DNS with reasonable accuracy. Finally, DNS is used to analyze the mechanisms of ITA modes.

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“…Yet, in the theory of Preetham et al The analytical analysis of flame dynamics has been, recently, extended to the time domain by Blumenthal et al [33]. These authors derived expressions for the temporal response of two different flame configurations subjected to an impulse [33]. Through spectral analysis of their temporal impulse response, Blumenthal et al…”

Section: Introductionmentioning

confidence: 99%

“…In this theory the phase speed of the flame disturbances is not necessarily the same as the mean flow speed and can vary freely [32]. Yet, in the theory of Preetham et al The analytical analysis of flame dynamics has been, recently, extended to the time domain by Blumenthal et al [33]. These authors derived expressions for the temporal response of two different flame configurations subjected to an impulse [33].…”

Section: Introductionmentioning

confidence: 99%

Response of a conical, laminar premixed flame to low amplitude acoustic forcing – A comparison between experiment and kinematic theories

Karimi

2014

Energy

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This paper presents an experimental study on the dynamics of a ducted, conical, laminar premixed flame subjected to low amplitude acoustic excitation from upstream. The heat release response of the flame to velocity disturbances is investigated through measurement of the so called 'flame transfer function' for a wide range of forcing frequencies. The results are compared with those predicted by the existing linear kinematic theories. It is observed that these theories are in general agreement with the experiment, although there exist some disparities. A detailed comparison of the experimental data with the kinematic theories shows that the phase speed of flame disturbances has an essential influence upon the level of agreement between the theory and experiment. The data set presented in this work complements that reported in an earlier study. In keeping with others, visualisation of the excited flames clearly shows that the flame response includes waves on the flame front which are formed at the base and then convect along the flame.

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Novel perspectives on the dynamics of premixed flames

Cited by 52 publications

References 25 publications

A systems perspective on non-normality in low-order thermoacoustic models: Full norms, semi-norms and transient growth

A systems perspective on non-normality in low-order thermoacoustic models: Full norms, semi-norms and transient growth

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Response of a conical, laminar premixed flame to low amplitude acoustic forcing – A comparison between experiment and kinematic theories

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