Computation of Forced Premixed Flames Dynamics

Ruan, S.; Dunstan, Thomas D.; Swaminathan, Nedunchezhian; Balachandran, Ramanarayanan

doi:10.1080/00102202.2016.1174117

Cited by 14 publications

(10 citation statements)

References 56 publications

(65 reference statements)

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“…At lower forcing amplitude A < 0.2 when the flame response is linear, both the current LES and previous numerical studies correctly reproduce the FDF gain from the experiment. Nevertheless, the current LES provides better predictions as compared to previous URANS [22] and LES results [23] especially at A = 0.64. This suggests that the ability of the TFSD approach to represent non-equilibrium effects on FSD transport is able to better capture the flame dynamics for saturation.…”

Section: Resultsmentioning

confidence: 56%

“…16a, b and c respectively. Results computed from the current LES study (red circles), along with results than previous LES [23] (blue diamonds) and URANS [22] (green triangle) investigations are overlaid on the experimental curve from OH* and CH* chemiluminescence. Good agreement between the present LES predictions with experimental results is obtained for the FDF amplitude.…”

Section: Resultsmentioning

confidence: 99%

“… where H f is the heat of formation, ρ u is the density of the unburnt mixture, S L is the laminar flame speed and Σ is the FSD. As discussed previously [ 22 , 23 ], the integration area for the experiment was based on a measurement window of length 55 mm, as opposed to the full combustion chamber of length 80 mm. Nevertheless, in the previous LES study by Han et al [ 23 ], the difference between the global heat release obtained using these measurement windows was found to be small and the heat release obtained from the total measurement window was therefore used.…”

Section: Resultsmentioning

confidence: 99%

“…16 a Normalised integrated heat release and b gain of the FDF c phase of the FDF. Current LES ( red circle ); previous LES [ 23 ] ( blue diamonds ) and URANS [ 22 ] ( green triangle ) …”

Section: Resultsmentioning

confidence: 99%

“…Armitage et al [ 21 ] performed a URANS simulation to capture the flame structure in the presence of strong vortex rollup and FDF of the bluff-body premixed flame. A later URANS study by Ruan et al [ 22 ] investigated the effects of chemistry on the forced flame behaviour. They found that while changes in chemical kinetics yield differences in flame length and spatial heat release, its effect on the FDF is small.…”

Section: Introductionmentioning

confidence: 99%

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LES of Nonlinear Saturation in Forced Turbulent Premixed Flames

Lee

Cant

2017

Flow Turbulence Combust

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The mechanisms for nonlinear saturation of a bluff-body stabilised turbulent premixed flame are investigated using LES with the transported flame surface density (TFSD) approach to combustion modelling. The numerical simulation is based on a previous detailed experimental investigation. Results for both the unforced non-reacting and reacting flows are validated against experiment, demonstrating that the fundamental flow features and predicted flame structure are well captured. Key terms in the FSD transport equation are then used to describe the generation and destruction of flame surface area for the unforced reacting flow. In order to investigate the non-linear response of the unsteady heat release rate to acoustic forcing, four harmonically forced flames are considered having the same forcing frequency (160 Hz) but different amplitudes of 10 %, 25 %, 50 % and 64 % of the mean inlet velocity. The flame response is characterised using the Flame Describing Function (FDF). Accurate prediction of the FDF is obtained using the current approach. The computed forced flame structure matches well with the experiment, where effects of shear layer rollup and growth of the vortices on the flame can be clearly observed. Transition to nonlinearity is also observed in the computed FDF. The mechanisms leading to the saturation of the flame response in the higher amplitude case are characterised by inspecting the terms in the FSD transport equation at conditions when the integrated heat release is at its maximum and minimum, respectively. Pinch-off and flame rollup can be seen in snapshots taken at the phase angle of maximum integrated heat release. Conversely, intense vortex shedding and flame-sheet collapse around the shear-layer, as well as small-scale destruction of flame elements in the wake, can be seen in snapshots taken at the phase angle of minimum integrated heat release. The pivotal role of FSD destruction on nonlinear saturation of the flame response is confirmed through the analysis of phase-averaged terms in the FSD transport equation taken at different locations. The phase-averaged subgrid curvature term is found to concentrate in the cusps and downstream regions where flame annihilation is dominant.

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Section: Resultsmentioning

confidence: 56%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…16 a Normalised integrated heat release and b gain of the FDF c phase of the FDF. Current LES ( red circle ); previous LES [ 23 ] ( blue diamonds ) and URANS [ 22 ] ( green triangle ) …”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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LES of Nonlinear Saturation in Forced Turbulent Premixed Flames

Lee

Cant

2017

Flow Turbulence Combust

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Scaling of Flame Describing Functions in Premixed Swirling Flames

Kallifronas

Ahmed

Massey

et al. 2023

Flow Turbulence Combust

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Predicting the response of swirling flames subjected to acoustic perturbations poses significant challenges due to the complex nature of the flow. In this work, the effect of swirl number on the Flame Describing Function (FDF) is explored through a computational study of four bluff-body stabilised premixed flames with swirl numbers ranging between 0.44 and 0.97 and at forcing amplitudes of 7% and 25% of the mean bulk velocity. The LES model used for the simulations is validated by comparing two of those flames to experiments. The comparison is observed to be good with the computations capturing the unforced flow structure, flame height and FDF behaviour. It is found that changes in the swirl number can affect the location of the minima and maxima of the FDF gain in the frequency space. These locations are not affected by changes in the forcing amplitude, but the gain difference between the minima and the maxima is reduced as the forcing amplitude is increased. It is then attempted to scale the FDF using Strouhal numbers based on two different flame length scales. A length scale based on the axial height of the maximum heat release rate per unit length leads to a good collapse of the FDF gain curves. However, it is also observed that flow instabilities present in the flow can affect the FDF scaling leading to an imperfect collapse.

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Influence of fuel plenum on thermoacoustic oscillations inside a swirl combustor

Chen

Swaminathan

2020

Fuel

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Computation of Forced Premixed Flames Dynamics

Cited by 14 publications

References 56 publications

LES of Nonlinear Saturation in Forced Turbulent Premixed Flames

LES of Nonlinear Saturation in Forced Turbulent Premixed Flames

Scaling of Flame Describing Functions in Premixed Swirling Flames

Influence of fuel plenum on thermoacoustic oscillations inside a swirl combustor

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