Identification of the Flame Describing Function of a Premixed Swirl Flame from LES

Krediet, H.J.; Beck, Christian; Krebs, Werner; Schimek, Sebastian; Paschereit, Christian Oliver; Kok, Jacobus B.W.

doi:10.1080/00102202.2012.663981

Cited by 81 publications

(35 citation statements)

References 13 publications

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“…This was encouraging for the usefulness of the coupled hybrid approach. An incompressible LES solver was also used to study an acoustically forced flame by Krediet et al [37,38] under swirl premixed conditions. Experimentally, the acoustic forcing was provided by speakers mounted in the upstream duct: this was imitated numerically by introducing velocity excitation at the inlet in the simulations.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Han

Morgans

2015

Combustion and Flame

103

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Numerical simulations were used to characterise the non-linear response of a turbulent premixed flame to acoustic velocity fluctuations. The test flame simulated was the bluff body stabilised flame which has been the subject of a detailed experimental study (Balachandran et al., 2005, Combustion & Flame). Simulations were performed using Large Eddy Simulation (LES) via the open source Computational Fluid Dynamics (CFD) software, Code S aturne, with combustion modelled by combining a Flame Surface Density (FSD) method with a fractal approach for the wrinkling factor. The cold flow field and the unforced reacting flow were used for preliminary code validation. In order to characterise the non-linear response of the unsteady heat release rate to acoustic forcing, a harmonically varying velocity fluctuation, for which both the forcing frequency and normalised forcing amplitude were varied, was imposed. The flame response was characterised via a Flame Describing Function (FDF), also known as a nonlinear flame transfer function, for which the gain and phase shift depend on forcing amplitude as well as forcing frequency. The response at four frequencies was compared to experimental data in detail, confirming that the LES results captured both the qualitative flame dynamics and the quantitative response of the heat release rate with very reasonable accuracy. The full FDF was then obtained across more frequencies, again showing a good fit with the experimental data, other than for a slight under-prediction in gain, most probably due to neglecting the effect of wall heat loss and the effect of combustion modelling. The agreement was significantly better than has been obtained previously for this test case using numerical simulations. Finally, it was found that increasing combustor length had little affect on the flame response, which may prove useful for future long combustor stability and limit cycle analysis. This work thus confirms that LES, in this case via the open source Code S aturne, provides a useful tool for characterising the response of lean premixed turbulent flames.

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Section: Introductionmentioning

confidence: 99%

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Han

Morgans

2015

Combustion and Flame

103

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“…The flow variables, F, were expressed as resolvablẽand subgrid, , level quantities using a Favreweighted filter,̃= / . The resolved scale flow quantities are described by the following equations [10,13,15,16]: continuity is…”

Section: Numerical Models and Solution Proceduresmentioning

confidence: 99%

“…Turbulent transport is modelled with the dynamic Smagorinsky model embodied in the basic software [6,10,11] with the dynamic Smagorinsky coefficient C s in the sgs eddy viscosity constrained for stability between 0 and 0.23. A time-dependent SIMPLE algorithm [10,15] was employed to treat pressure-velocity coupling. Time discretization was obtained with a secondorder accurate scheme, and the time step was chosen to maintain a maximum Courant number between 0.4 and 0.6.…”

Section: Numerical Models and Solution Proceduresmentioning

confidence: 99%

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Effect of Modulation of the Inlet Velocity and Equivalence Ratio Gradients on the Stabilization of Stratified Axisymmetric Bluff-Body Flames

Paterakis

Koutmos

2018

Journal of Combustion

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An investigation of ultralean stratified, disk stabilized, propane flames operated with acoustic modulation of the inlet velocity and fuel-air mixture profiles is presented. Transverse acoustic forcing was applied to the air, upstream of a double-cavity premixer section, formed along three concentric disks, which fueled the stabilization region with a radial mixture gradient. Measurements and supporting Large Eddy Simulations with a nine-step mechanism for propane combustion were performed to evaluate variations in the ultralean flame characteristics under forced and unforced conditions. The effects of forcing on the heat release profiles and on the interaction of the toroidal flame with the recirculation region are examined and discussed. The impact of the acoustic excitation of inlet conditions on the local extinction behavior is, also, assessed by monitoring a local stability criterion and by analyzing phase-resolved chemiluminescence images.

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“…• Type 2: Imposed wall temperatures [23][24][25][26][27] : when experimental data on wall temperatures is available, imposing them as boundary conditions for LES may be a solution. Note that this can be a dangerous methodology: imposing a high local wall temperature may for example, force the flame to anchor at this point, diminishing the predictive quality of the method by forcing the solution artificially.…”

Section: Introductionmentioning

confidence: 99%

Coupling heat transfer and large eddy simulation for combustion instability prediction in a swirl burner

Kraus

Selle

Poinsot

2018

Combustion and Flame

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao. Large eddy simulations (LES) of combustion instabilities are often performed with simplified thermal wall boundary conditions, typically adiabatic walls. However, wall temperatures directly affect the gas temperatures and therefore the sound speed field. They also control the flame itself, its stabilization characteristics and its response to acoustic waves, changing the flame transfer functions (FTFs) of many combustion chambers. This paper presents an example of LES of turbulent flames fully coupled to a heat conduction solver providing the temperature in the combustor walls. LES results obtained with the fully coupled approach are compared to experimental data and to LES performed with adiabatic walls for a swirled turbulent methane/air burner installed at Engler-Bunte-Institute, Karlsruhe Institute of Technology and German Aerospace Center (DLR) in Stuttgart. Results show that the fully coupled approach provides reasonable wall temperature estimations and that heat conduction in the combustor walls strongly affects both the mean state and the unstable modes of the combustor. The unstable thermoacoustic mode observed experimentally at 750 Hz is captured accurately by the coupled simulation but not by the adiabatic one, suggesting that coupling LES with heat conduction solvers within combustor walls may be necessary in other configurations in order to capture flame dynamics.

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Identification of the Flame Describing Function of a Premixed Swirl Flame from LES

Cited by 81 publications

References 13 publications

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Simulation of the flame describing function of a turbulent premixed flame using an open-source LES solver

Effect of Modulation of the Inlet Velocity and Equivalence Ratio Gradients on the Stabilization of Stratified Axisymmetric Bluff-Body Flames

Coupling heat transfer and large eddy simulation for combustion instability prediction in a swirl burner

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