Velocity and Flame Wrinkling Characteristics of a Transversely Forced, Bluff-Body Stabilized Flame, Part II: Flame Response Modeling and Comparison with Measurements

Acharya, Vishal; Emerson, Benjamin; Mondragon, Ulises; Shin, Dong-Hyuk; Brown, Christopher T.; McDonell, Vincent; Lieuwen, Tim

doi:10.1080/00102202.2013.777715

Cited by 14 publications

(8 citation statements)

References 43 publications

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“…denotes some suitable reference perturbation velocity [76]. The analysis using the FTF has been used for both premixed [76,93,127,179] and non-premixed flames as well [171,180,181]. While these transfer functions can be quite complex, a commonly used simplification for the flame response is the so-called…”

Section: Figuresmentioning

confidence: 99%

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

O’Connor

Acharya

Lieuwen

2015

Progress in Energy and Combustion Science

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302

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Thermoacoustic oscillations associated with transverse acoustic modes are routinely encountered in combustion chambers. While a large literature on this topic exists for rockets, no systematic reviews of transverse oscillations are available for airbreathing systems, such as in boilers, aircraft engines, jet engine augmentors, or power generating gas turbines. This paper reviews work on the problem for air-breathing systems, summarizing experimental, modeling, and active control studies of transverse oscillations. It then details the key physical processes controlling these oscillations by describing transverse acoustic wave motions, the effect of transverse acoustic waves on hydrodynamic instabilities, and the influence of acoustic and hydrodynamic fluid motions on the unsteady heat release. This paper particularly emphasizes the distinctions between the direct and indirect effect of transverse wave motions, by arguing that the dominant effect of the transverse acoustics is to act as the "clock" that controls the frequency and modal structure of the disturbance field. However, in many instances, it is the indirect axial flow disturbances at the nozzles (driven by pressure oscillations from the transverse mode), and the vortices that they excite, that cause the dominant heat release rate oscillations. Throughout the review, we discuss issues associated with simulating or scaling instabilities, either in subscale experimental geometries or by attempting to understand instability physics using identical nozzle hardware during axial oscillations of the same frequency as the transverse mode of interest. This review closes with a model problem that integrates many of these controlling elements, as well as recommendations for future research needs.

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Section: Figuresmentioning

confidence: 99%

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

O’Connor

Acharya

Lieuwen

2015

Progress in Energy and Combustion Science

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302

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“…Although it provided some insight into the mechanism by which fuel staging suppresses instability, it cannot provide information about local or instantaneous flame dynamics, which the LIF technique can. As the flame oscillates laterally, a result of vortex rollup in the shear layers excited by the longitudinal acoustic mode, the flame sheet area oscillates as well; comparisons between this technique and flame area tracking using level-set methods [30][31], even at high turbulence intensities [32][33], have shown good agreement between flame displacement and flame area metrics. The edge displacement time series (L') is constructed by tracking the lateral displacement of the flame edges as a function of downstream distance and time.…”

Section: Discussionmentioning

confidence: 94%

Flame Edge Dynamics and Interaction in a Multinozzle Can Combustor With Fuel Staging

Doleiden

Culler

Tyagi

et al. 2019

Journal of Engineering for Gas Turbines and Power

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The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines are necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multinozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancelation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 deg (∼114 deg), suggesting that the phase-cancelation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.

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“…A significant experimental and modeling literature exists on the response of premixed flames to harmonic flow disturbances [1][2][3][4][5]. Measurements have experimentally characterized both the local space-time dynamics of wrinkles on laminar flames [6,7], as well as the spatially integrated heat release [8]. These measurements show that wrinkles are excited at the flame stabilization point and locations of spatial non-uniformities in disturbance velocity, and subsequently convect down the flame.…”

Section: Introductionmentioning

confidence: 99%

Spatio-temporal evolution of harmonic disturbances on laminar, non-premixed flames: Measurements and analysis

Magina

Steele

Emerson

et al. 2017

Combustion and Flame

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This paper analyzes the dynamics of harmonically forced, non-premixed flames, both experimentally and computationally. Prior theory has made a number of predictions on how wrinkles on non-premixed flamelets are excited by flow disturbances, convect axially, and evolve in disturbance magnitude, including setting up interference patterns in wrinkle disturbance magnitude. The objective of this study was to obtain measurements from forced flames to determine if these features are present, and to compare the gain/phase of these wrinkles with predictions using the measured velocity field as inputs.High speed PIV data was taken on a coflowing methane-air diffusion flame, equipped with speakers for harmonic forcing, over a variety of flow velocities, forcing frequencies, and forcing amplitudes. These measured velocity fields were used as inputs to a Z -equation solver, and the resulting space-time dynamics of iso-Z surfaces were extracted from the Z field solutions. Both experimental and numerical results show that flame wrinkles propagate axially at the mean flow velocity, a result consistent with previous analytical findings. These wrinkles start with near zero magnitude at the fuel tube lip and grow with downstream distance, until peaking at some axial location. Further downstream, the wrinkle magnitude modulates, indicative of interference effects which have been previously predicted in analytical studies.

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Velocity and Flame Wrinkling Characteristics of a Transversely Forced, Bluff-Body Stabilized Flame, Part II: Flame Response Modeling and Comparison with Measurements

Cited by 14 publications

References 43 publications

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

Flame Edge Dynamics and Interaction in a Multinozzle Can Combustor With Fuel Staging

Spatio-temporal evolution of harmonic disturbances on laminar, non-premixed flames: Measurements and analysis

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