Shear Layer Flame Stabilization Sensitivities in a Swirling Flow

Chterev, Ianko; Foley, C. W.; Noble, David R.; Ochs, Bradley A.; Seitzman, Jerry M.; Lieuwen, Tim

doi:10.1115/gt2012-68513

Cited by 7 publications

(20 citation statements)

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“…Schefer et al reported the dependency of flame macrostructures on fuel composition through hydrogen addition to a premixed air-methane mixture [11]. Chterev et al explored the effect of equivalence ratio and preheat temperature as well as geometrical features like the swirl number and the centerbody design on the different mean flame configurations [12,13]. The dependency of flame macrostructures on the Reynolds number has been also investigated.…”

Section: Introductionmentioning

confidence: 99%

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Taamallah¹,

LaBry²,

Shanbhogue³

et al. 2015

Journal of Engineering for Gas Turbines and Power

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In this paper, we conduct an experimental investigation to study the link between the flame macroscale structure-or flame brush spatial distribution-and thermo-acoustic instabilities, in a premixed swirl-stabilized dump combustor. We operate the combustor with premixed methane-air in the range of equivalence ratio (/) from the lean blowout limit to / ¼ 0:75. First, we observe the different dynamic modes in this lean range as / is raised. We also document the effect of / on the flame macrostructure. Next, we examine the correspondence between dynamic mode transitions and changes in flame macrostructure. To do so, we modify the combustor length-by downstream truncationwithout changing the underlying flow upstream. Thus, the resonant frequencies of the geometry are altered allowing for decoupling the heat release rate fluctuations and the acoustic feedback. Mean flame configurations in the modified combustor and for the same range of equivalence ratio are examined, following the same experimental protocol. It is found that not only the same sequence of flame macrostructures is observed in both combustors but also that the transitions occur at a similar set of equivalence ratio. In particular, the appearance of the flame in the outside recirculation zone (ORZ) in the long combustor-which occurs simultaneously with the onset of instability at the fundamental frequency-happens at similar / when compared to the short combustor, but without being in latter case accompanied by a transition to thermo-acoustic instability. Then, we interrogate the flow field by analyzing the streamlines, mean, and rms velocities for the nonreacting flow and the different flame types. Finally, we focus on the transition of the flame to the ORZ in the acoustically decoupled case. Our analysis of this transition shows that it occurs gradually with an intermittent appearance of a flame in the ORZ and an increasing probability with /. The spectral analysis of this phenomenon-we refer to as "ORZ flame flickering"-shows the presence of unsteady events occurring at two distinct low frequency ranges. A broad band at very low frequency in the range $(1 Hz-10 Hz) associated with the expansion and contraction of the inner recirculation zone (IRZ) and a narrow band centered around 28 Hz which is the frequency of rotation of the flame as it is advected by the ORZ flow.

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Section: Introductionmentioning

confidence: 99%

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Taamallah¹,

LaBry²,

Shanbhogue³

et al. 2015

Journal of Engineering for Gas Turbines and Power

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“…Combustor Design The experimental facility is was discussed in Ref. [36] and can be divided into a reactant supply system, flow preconditioning and fuel/air mixing, premixer, combustor, and exhaust sections. Upon entering the premixer section the outer and inner diameter of the test section are smoothly transitioned to the desired dimensions of 62 mm for the outer diameter and 36 mm for the inner or centerbody diameter.…”

Section: Methodsmentioning

confidence: 99%

“…The second feature of note is the decreased jet spread angle as a result of the hot products escaping from the OSL stabilized flame. As discussed previously [36], the transition points between these different configurations were characterized as a function of fuel/air ratio, preheat temperature, bulkhead temperature, and center body temperature. Figure 17 shows a typical flame configuration run, showing the OSL stabilization and blowoff lines.…”

Section: Flame Shape IIImentioning

confidence: 99%

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Flame and Flow Topologies in an Annular Swirling Flow

Chterev

Foley

Kostka

et al. 2013

Volume 1B: Combustion, Fuels and Emissions

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A variety of different flame configurations and heat release distributions, with their associated flow fields, can exist in high swirl, annular flows. Each of these different configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle life, and liner heating. These different configurations arise because at least three flame stabilization locations are present, associated with the inner and outer shear layers of the annulus, and the stagnation point of the vortex breakdown region. This paper discusses the flame and flow topologies that exist in these flows. These results illustrate the importance of the sensitivity of flame configurations to geometric (such as centerbody size and shape, combustor diameter, exhaust contraction) and operational (e.g., bulkhead temperature, preheat temperature, fuel air ratio) parameters. We particularly emphasize the centerbody shape as differentiating between two different families of flame shapes. Results are shown illustrating the time averaged and instantaneous flame shape and flow fields, using high speed PIV, OH-PLIF, and luminosity imaging.

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“…Several researchers reported the existence of different flame shapes in swirl-stabilized combustion. These have been previously documented as function of fuel composition [7][8][9], equivalence ratio and preheat temperature [5,10] and Reynolds number [11], swirl number [12] as well as centerbody geometry [4]. Most of these studies reported the following flames although named differently: a columnar flame (I); a bubble-columnar flame (II); a single conical flame with a flame stabilized along the ISL (flame III); and a double conical flame with an additional continuous flame front stabilized in the ORZ and/or along the OSL (flame IV).…”

Section: Introductionmentioning

confidence: 99%

Transition From a Single to a Double Flame Structure in Swirling Reacting Flows: Mechanism, Dynamics, and Effect of Thermal Boundary Conditions

Taamallah

Shanbhogue

Sanusi

et al. 2015

Volume 5C: Heat Transfer

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We examine experimentally the transition from a single flame stabilized along the inner shear layer (ISL) to a double flame stabilized along both the inner and the outer shear layers (OSL) and spreading over the outside recirculation zone (ORZ) in a fully premixed swirl-stabilized combustor. This work is mainly driven by previous studies demonstrating the link between this transition in the flame macrostructure and the onset of thermo-acoustic instabilities [1,2]. Here, we examine the transition mechanism under thermo-acoustically stable conditions as well as the dominant flow and flame dynamics associated with it. In addition, we explore the role of changing the thermal boundary conditions around the ORZ and its effect on the presence or absence of the flame there. We start by analyzing the two flames bounding the transition, namely the single conical flame stabilized along the ISL (flame III 1 ) and the double conical flames with reactions * Corresponding author -email: sofiene@mit.edu 1 Same flame configuration nomenclature as in [1][2][3][4][5][6] taking place in the ORZ (flame IV). A dual chemiluminescence approach -using two cameras with a narrow field of view focused on the ORZ -is undertaken to track the progression of the flame as it reaches the ORZ. During the transition, the flame front, initially stabilized along the ISL, is entrained by OSL vortices close to where the turbulent jet impinges on the wall, leading to the ignition of the reactants in the ORZ and the ultimately the stabilization of the flame along the outer shear layer (OSL). This ORZ flame is also subject to extinction when the equivalence ratio (φ ) is between values corresponding to flames III and IV. For φ lower than the critical transitional value, the flame kernel originating from the ISL-stabilized flame is shown to reach the ORZ but fails to grow and quickly disappears. For φ higher than the critical value, the flame kernel expands as it is advected by the ORZ flow and ultimately ignites the reactants recirculating in the ORZ. Sudden and extreme peak-to-peak values of the overall heat release rate are found to be concomitant with the ignition and extinction of the ORZ reactants. Finally, Different ther-

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Shear Layer Flame Stabilization Sensitivities in a Swirling Flow

Cited by 7 publications

References 0 publications

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

Flame and Flow Topologies in an Annular Swirling Flow

Transition From a Single to a Double Flame Structure in Swirling Reacting Flows: Mechanism, Dynamics, and Effect of Thermal Boundary Conditions

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