Premixed Flames Excited by Helical Disturbances: Flame Wrinkling and Heat Release Oscillations

Acharya, Vishal; Shin, Dong-Hyuk; Lieuwen, Tim

doi:10.2514/1.b34883

Cited by 44 publications

(21 citation statements)

References 54 publications

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“…These oscillations cancel each other on opposite sides of the flame, an observation that is consistent with theoretical analysis of axisymmetric flames [7,[47][48][49]. The phase averaged [40] images of the vertical cuts of the flame were seen to be different view angles of a stationary structure.…”

Section: Flow Instabilitiessupporting

confidence: 79%

“…For nonaxisymmetric modes (m 7^ 0), the integral over 0 is zero, which implies that only the axisymmetric m = 0 mode contributes to the global flame area. An important implication of this result is that helical modes, while introducing substantial wrinkling of the flame front, actually lead to no fluctuations in flame surface area in axisymmetric flows [49], a result that is also consistent with experimental observations from Moeck et al [45]. This has important implications when it comes to the use of flow field data from experiments as inputs to the model.…”

Section: Theoretical Formulationsupporting

confidence: 79%

“…6 Schematic of the lifted swiri-stabilized premixed flame time averaged flame position is shown by the solid line, and the perturbed flame by the dashed line. The remainder of this section presents the key equations that describe the model, summarized from earlier work[49,56],…”

mentioning

confidence: 99%

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Dynamics of a Transversely Excited Swirling, Lifted Flame: Flame Response Modeling and Comparison With Experiments

Acharya

Malanoski²,

Aguilar³

et al. 2014

Journal of Engineering for Gas Turbines and Power

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This paper describes measurements and modeling of the response of a swirling, lifted fiame to transverse fiow excitation. The problem is motivated by combustion instabilities associated with transverse acoustic modes of combustors. The developed formulation relates the unsteady fiame response characteristics to both the spatially filtered disturbance field and mean fiow field characteristics. Measured fiow and fiame features are used as model inputs in order to compare the global heat release fiuctuations with those measured from the experiment, showing quite good agreement. As such, this paper shows that, given sufficient fiow field information, the dynamic fiame response can be reasonably predicted from first-principles calculations with no empiricism. We also show that the strongly helical disturbances present in the fiow have minimal impact on the global response of axisymmetric fiâmes, as the local heat release fiuctuations that they induce cancel each other azimuthally.

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Section: Flow Instabilitiessupporting

confidence: 79%

Section: Theoretical Formulationsupporting

confidence: 79%

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Dynamics of a Transversely Excited Swirling, Lifted Flame: Flame Response Modeling and Comparison With Experiments

Acharya

Malanoski²,

Aguilar³

et al. 2014

Journal of Engineering for Gas Turbines and Power

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“…Due to the skew symmetric structure of the PVC, no integral heat release fluctuations are caused (Moeck et al, 2012). However, if the mean flow is not completely axisymmetric, analytical models predict integral heat Downloaded by [Northeastern University] at 00:52 19 November 2014 release fluctuations (Acharya et al, 2013), thus allowing for a coupling with thermoacoustic instabilities.…”

Section: Introductionmentioning

confidence: 99%

Impact of Steam-Dilution on the Flame Shape and Coherent Structures in Swirl-Stabilized Combustors

Steffen

Oberleithner

Paschereit

2014

Combustion Science and Technology

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Humidified gas turbines and steam-injected gas turbines are promising technologies to lower the emissions and increase the efficiency and fuel flexibility of gas turbines. In the current study, the influence of steam-dilution on swirl-stabilized methane and hydrogenfired flames is experimentally investigated at Reynolds numbers in the range of 22,000 to 32,000. Velocity fields and flame positions were measured using high-speed particle image velocimetry and OH * chemiluminescence. An extension of the quantitative light sheet technique was employed to estimate the temperature fields. The combined results reveal strong changes in the flame position, the velocity field, and the temperature field with increasing rates of steam dilution. In particular, three different flow and flame patterns are encountered: At dry conditions, a V-shaped flame stabilizes in a broad inner recirculation zone with low local turbulent kinetic energy; at moderate steam content, the flame changes into a trumpet-like shape; and at very high rates of steam-dilution, the flame detaches and shows an annular shape. The associated coherent flow structures are extracted from the particle image velocimetry data employing proper orthogonal decomposition. The isothermal flow is dominated by a helical instability arising near the combustor inlet. This structure is completely suppressed for the dry flame and reappears for the heavily steam-diluted detached flame with a similar shape and frequency as for the isothermal case. The flow field of the trumpet-like flame at intermediate to high steam dilution rates features a helical instability of lower frequency that is located further downstream than in the isothermal and very wet case. A conceptional explanation is presented that relates the suppression of the helical instability to the specific encountered temperature fields and flame shapes.

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“…For annular combustors, depending upon the azimuthal location of the nozzle in the standing wave, they would excite different helical disturbances and thus differing flame response [6,8] The Flame Transfer function (FTF), defined as the ratio of the spatially integrated heat release to a reference velocity perturbation has been used extensively to characterize the global flame response of premixed flame. In earlier work, the authors showed that this quantity was zero for all helical modes ( 0 m  ) and that only the 0 m  mode contributed to the FTF when the timeaveraged mean flame was axisymmetric [39]. In other words, although helical, 0 m  , modes may cause significant local space-time wrinkling of the flame, they lead to zero fluctuations in the spatially integrated heat release, due to phase cancellation in the azimuthal direction.…”

Section: Introductionmentioning

confidence: 96%

Premixed flame response to helical disturbances: Mean flame non-axisymmetry effects

Acharya

Lieuwen

2016

Combustion and Flame

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A key component of the thermoacoustic instability feedback mechanism is the excitation of hydrodynamic flow disturbances by narrowband acoustic fluctuations. In earlier work, we considered the response of time-averaged axisymmetric flames to helical disturbances. That study showed that although all helical modes cause local flame wrinkling, only the axisymmetric hydrodynamic mode, m = 0, contributes to the global heat release rate fluctuations. This paper extends this work to consider time-averaged flames that are non-axisymmetric. We show that distortions of the unforced flame shape changes its receptivity to helical disturbances, as it does not allow for the perfect destructive interference seen in axisymmetric flames. This results in a non-zero global flame response contribution from helical modes. Given that helical modes often have the largest amplitudes in jet flows, particularly those with swirl, these results show that the degree of non axisymmetry of the flame has an important influence in determining which hydrodynamic modes, axisymmetric or helical, control the global heat release response of the flame. These points have been illustrated with example calculations that show how different control parameters and the degree of time-averaged non-axisymmetry influence the global flame response. An important implication of these results relates to scaling results from simplified geometries where a round jet is placed inside a round enclosure, to more realistic ones (such as where multiple jets are placed next to each other) where the flame shape will be distorted from being perfectly circular.

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Premixed Flames Excited by Helical Disturbances: Flame Wrinkling and Heat Release Oscillations

Cited by 44 publications

References 54 publications

Dynamics of a Transversely Excited Swirling, Lifted Flame: Flame Response Modeling and Comparison With Experiments

Dynamics of a Transversely Excited Swirling, Lifted Flame: Flame Response Modeling and Comparison With Experiments

Impact of Steam-Dilution on the Flame Shape and Coherent Structures in Swirl-Stabilized Combustors

Premixed flame response to helical disturbances: Mean flame non-axisymmetry effects

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