Time-resolved blowoff transition measurements for two-dimensional bluff body-stabilized flames in vitiated flow

Tuttle, Steven G.; Chaudhuri, Swetaprovo; Kostka, Stanislav; Kopp-Vaughan, Kristin M.; Jensen, Trevor R.; Cetegen, Baki M.; Renfro, Michael W.

doi:10.1016/j.combustflame.2011.06.001

Cited by 46 publications

(9 citation statements)

References 28 publications

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“…Increased Ka values will be coupled with flame stretching [2,[7][8][9]11], meaning that localized extincitons are more likely to occur as the turbulence levels are increased. However, flame stretching is also a function of flame curvature [2,9].…”

Section: Resultsmentioning

confidence: 99%

“…The last column in Table 1 documents the mean blowout duration for each test case (text) as well as the standard deviation (σ) among the 10 trials for each turbulence level. The total blowout duration was calculated in a similar fashion used in [10,11,13], i.e. by identifying the time required for the C2*/CH* chemiluminescence intensity to decrease from a maximum stable value to a minimum constant value at blowout.…”

Section: Turbulence Tailoringmentioning

confidence: 99%

“…The intense velocity gradients within the shear layers invokes high strain rates along the flame boundary which stretch the flame and cause localized extinctions to occur [2,9,10]. If the equivalence ratio continues to decrease, the flame and shear layer interaction will intensify and there will be a greater number of localized extinction events along the flame [7,8,11]. This will continue to occur until a majority of the flame is extinguished and the recirculation zone can no longer reignite-incoming reactants; this is when global blowout occurs [2,7,8,11].…”

Section: Introductionmentioning

confidence: 99%

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The effects of turbulence on the lean blowout mechanisms of bluff-body flames

Morales

Reyes

Boxx

et al. 2021

Proceedings of the Combustion Institute

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The lean blowout mechanisms of premixed bluff-body flames are experimentally investigated at various turbulence intensities. Turbulence levels are varied using a novel turbulence generator, which combines static grid and fluidic jet impingement techniques. Three different turbulence levels are probed to study their effects on lean blowout. The three conditions span across the combustion regime diagram, from flamelets to broken reactions. For all three turbulence levels, the lean blowout process is induced through controlled fuel flow rate reduction. The transient blowout process is captured using three simultaneous high-speed diagnostic systems: particle image velocimetry (PIV), stereoscopic PIV (SPIV), and C2 * /CH * species measurements. The two PIV systems are used to resolve the instantaneous velocity and vorticity fields, and the C2 * /CH * species diagnostics allow for global equivalence ratios to be evaluated throughout the duration of blowout. The results show that the dynamics of lean blowout vary with turbulence intensity. At low turbulence levels, the flame experiences a global effect where the flame boundary interacts with the shear layer vorticity. This imparts high strain rates along the length of the flame, leading to blowout. As turbulence levels increase, the blowout mechanism becomes less dependent on flame and shear layer interactions and more driven by flame-turbulence interactions. At high turbulence conditions, flame-eddy interactions within the freestream augment flame stretching via increased flame straining and small-scale flame corrugations. Increased flame stretching disrupts the flame stabilization process, and ultimately results in blowout.

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Section: Resultsmentioning

confidence: 99%

Section: Turbulence Tailoringmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The effects of turbulence on the lean blowout mechanisms of bluff-body flames

Morales

Reyes

Boxx

et al. 2021

Proceedings of the Combustion Institute

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“…The crucial feature of swirl burners is the formation of a central recirculation zone (CRZ) which extends blowoff limits by recycling heat and active chemical species to the root of the flame in the burner exit [5][6]. Thus, the CRZ is one of the mechanisms for flame stabilization that through an aerodynamically decelerated region creates a point where the local flame speed and flow velocity match [7].…”

Section: Introductionmentioning

confidence: 99%

CFD predictions of Swirl burner aerodynamics with variable outlet configurations

Baej¹

2019

IJET

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Swirl stabilised combustion is one of the most widely used techniques for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using several gaseous blends at a constant power output. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by the blend and infer that it is governed by both the shear layer surrounding the Central Recirculation Zones (CRZ) and the gas composition.

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“…To describe the lean blowoff behaviour of swirl combustors under various fuel compositions, correlations have to be determined and simplified models developed to allow the implementation of fuel flexible technologies [4]. The crucial feature of swirl burners is the formation of a central recirculation zone (CRZ) which extends blowoff limits by recycling heat and active chemical species to the root of the flame in the burner exit [5][6]. Thus, the CRZ is one of the mechanisms for flame stabilization that through an aerodynamically decelerated region creates a point where the local flame speed and flow velocity match [7].…”

Section: Introductionmentioning

confidence: 99%

Modeling Effects of Outlet Nozzle Geometry on Swirling Flows in Gas Turbine

Baej

Akair

Diyaf

et al. 2018

Proceedings of First Conference for Engineering Sciences and Technology: Vol. 2

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Swirl stabilised combustion is one of the most successful technologies for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. The complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using isothermal case to recognize the the behavers of swirl. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by both the shear layer surrounding the Central Recirculation Zones (CRZ) and outlet configurations

show abstract

Time-resolved blowoff transition measurements for two-dimensional bluff body-stabilized flames in vitiated flow

Cited by 46 publications

References 28 publications

The effects of turbulence on the lean blowout mechanisms of bluff-body flames

The effects of turbulence on the lean blowout mechanisms of bluff-body flames

CFD predictions of Swirl burner aerodynamics with variable outlet configurations

Modeling Effects of Outlet Nozzle Geometry on Swirling Flows in Gas Turbine

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