Lean blowoff of bluff body stabilized flames: Scaling and dynamics

Shanbhogue, Santosh J.; Husain, Sajjad A.; Lieuwen, Tim

doi:10.1016/j.pecs.2008.07.003

Cited by 521 publications

(226 citation statements)

References 116 publications

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“…The mechanisms that lead to LBO in turbulent swirl-stabilized flames, however, are poorly understood owing to the complex interactions of chemistry, flow and transport. Previous studies of LBO dynamics have mainly focused on bluff-body stabilized flames as summarized in a recent review by Shanbhogue et al [1]. The LBO limit of swirl flames is therefore difficult to predict, and has to be determined experimentally.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of lean blowout of a swirl-stabilized flame in a gas turbine model combustor

Stöhr

Boxx

Carter

et al. 2011

Proceedings of the Combustion Institute

221

119

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Lean blowout (LBO) of a partially premixed swirl flame is studied using chemiluminescence imaging and simultaneous stereo-PIV and OH-PLIF measurements at repetition rates up to 5 kHz. The flame, which is operated with methane and air in a gas turbine model combustor at atmospheric pressure, features a pronounced precessing vortex core (PVC) at the inner shear layer. In the first part of the study, the stabilization mechanism of the flame close to LBO is investigated. The fields of velocity and OH show that near LBO there are essentially two regions where reaction takes place, namely the helical zone along the PVC and the flame root around the lower stagnation point. The zone along the PVC is favorable to the flame due to low strain rates in the vortex center and accelerated mixing of burned and fresh gas. The flame root, which is located close to the nozzle exit, is characterized by an opposed flow of hot burned gas and relatively fuel-rich fresh gas. Due to the presence of high strain rates, the flame root is inherently unstable near LBO, featuring frequent extinction and re-ignition. The blowout process, discussed in the second part of the study, starts when the extinction of the flame root persists over a critical length of time. Subsequently, the reaction in the helical zone can no longer be sustained and the flame finally blows out. The results highlight the crucial role of the flame root, and suggest that well-aimed modifications of flow field or mixture fraction in this region might shift the LBO limit to leaner conditions.

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Section: Introductionmentioning

confidence: 99%

Dynamics of lean blowout of a swirl-stabilized flame in a gas turbine model combustor

Stöhr

Boxx

Carter

et al. 2011

Proceedings of the Combustion Institute

221

119

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“…The dynamics of the downstream flow behind the bluff-body was largely driven by the shear layer and wake processes alone. For this Reynolds number range (sub-critical flow regime, 1000 < Re < 200000), both absolute and convective instabilities are present -asymmetric vortex shedding (the Bénard/von Kármán instability) and Kelvin-Helmholtz instability of the separated shear layer [57]. Investigation of the shear-layer instability was out of scope of the present work.…”

Section: Sas Non-reacting Flow Resultsmentioning

confidence: 94%

Reynolds-Averaged, Scale-Adaptive and Large-Eddy Simulations of Premixed Bluff-Body Combustion Using the Eddy Dissipation Concept

Lysenko¹,

Ertesvåg

2017

Flow Turbulence Combust

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A lean premixed propane/air bluff-body stabilized flame (Volvo test rig) is calculated using the Scale-Adaptive Simulation turbulence model (SAS) and Large-Eddy simulations (LES) as well as the conventional Reynoldsaveraged approach (RAS). RAS and SAS are closed by the standard k-ǫ and the k-ω Shear Stress Transport (SST) turbulence models, respectively. The conventional Smagorinsky and the k-equation sub-grid scales models are used for the LES closure. Effects of the sub-grid scalar flux modeling using the classical gradient hypothesis and Clark's tensor diffusivity closures both for the inert and reactive LES flows are discussed. The Eddy Dissipation Concept (EDC) is used for the turbulence-chemistry interaction. It assumes that molecular mixing and the subsequent combustion occur in the 'fine structures' (smaller dissipative eddies, which are close to the Kolmogorov scales). Assuming the full turbulence energy cascade, the characteristic length and velocity scales of the 'fine structures' are evaluated using different turbulence models (RAS, SAS and LES). The finite-rate chemical kinetics is taken into account by treating the 'fine structures' as constant pressure and adiabatic homogeneous reactors, calculated as a system of ordinary-differential equations (ODEs) described by a Perfectly Stirred Reactor (PSR) concept. Several further enhancements to model the PSRs are proposed, including a new Livermore Solver (LSODA) for integrating stiff ODEs and a new correction to calculate the PSR time scales. All models have been implemented as a stand-alone application edcPisoFoam based on the OpenFOAM technology. Additionally, several RAS calculations were performed using the Turbulence Flame Speed Closure model in Ansys Fluent to assess effects of the heat losses by modeling the conjugate heat transfer between the bluff-body and the reactive flow. Effects of the turbulence Schmidt number on RAS results are discussed as well. Numerical results are compared with available experimental data. Reasonable consistency between experimental data and numerical results provided by RAS, SAS and LES is observed. In general, there is satisfactory agreement between present LES-EDC simulations, numerical results by other authors and measurements without any major modification to the EDC closure constants, which gives a quite reasonable indication on the adequacy and accuracy of the method and its further application for turbulent premixed combustion simulations.

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“…When bluff body is used as a flame holder, the incoming fuel and oxidizer mixture is ignited by the hot combustion products recirculating in a wake structure formed behind the bluff body. This stabilization mechanism has been investigated extensively by many researchers [6][7][8][9][10][11][12]. Many studies associated with bluff body stabilization mechanism focus on premixed combustion systems, where premixed fuel and oxidizer are provided to the combustion zone and thus complex physics that controls mixing process can be neglected.…”

Section: Ppbb Burnermentioning

confidence: 99%

Application of a Central Composite Design for the Study of NOx Emission Performance of a Low NOx Burner

2015

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Abstract:In this study, the influence of various factors on nitrogen oxides (NOx) emissions of a low NOx burner is investigated using a central composite design (CCD) approach to an experimental matrix in order to show the applicability of design of experiments methodology to the combustion field. Four factors have been analyzed in terms of their impact on NOx formation: hydrogen fraction in the fuel (0%-15% mass fraction in hydrogen-enriched methane), amount of excess air (5%-30%), burner head position (20-25 mm from the burner throat) and secondary fuel fraction provided to the burner (0%-6%). The measurements were performed at a constant thermal load equal to 25 kW (calculated based on lower heating value). Response surface methodology and CCD were used to develop a second-degree polynomial regression model of the burner NOx emissions. The significance of the tested factors over their respective ranges has been evaluated using the analysis of variance and by the consideration of the coefficients of the model equation. Results show that hydrogen addition to methane leads to increased NOx emissions in comparison to emissions from pure methane combustion. Hydrogen content in a fuel is the strongest factor affecting NOx emissions among all the factors tested. Lower NOx formation because of increased excess air was observed when the burner was fuelled by pure methane, but this effect diminished for hydrogen-rich fuel mixtures. NOx emissions were slightly reduced when the burner head was shifted closer to the burner outer tube, whereas a OPEN ACCESSEnergies 2015, 8 3607 secondary fuel stream provided to the burner was found to have no impact on NOx emissions over the investigated range of factors.

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Lean blowoff of bluff body stabilized flames: Scaling and dynamics

Cited by 521 publications

References 116 publications

Dynamics of lean blowout of a swirl-stabilized flame in a gas turbine model combustor

Dynamics of lean blowout of a swirl-stabilized flame in a gas turbine model combustor

Reynolds-Averaged, Scale-Adaptive and Large-Eddy Simulations of Premixed Bluff-Body Combustion Using the Eddy Dissipation Concept

Application of a Central Composite Design for the Study of NOx Emission Performance of a Low NOx Burner

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