Swirling flame dynamics and combustion instability

An investigation into the response of non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0–315 Hz) and swirl intensities (S = 0.09 and 0.34) is carried out. Perturbations are generated using a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes |u′/Uavg| in the 0.03–0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. Flame heat release is quantitatively measured and simultaneously imaged using a photomultiplier (PMT) and a phase-locked CCD camera. Both of which are fitted with 430nm bandpass filters for observing CH*chemiluminescence. The flame response is observed to exhibit a low-pass filter characteristic with minimal flame response beyond pulsing frequencies of 200Hz. Flames at lower fuel flow rates are observed to remain attached to the central fuel pipe at all acoustic pulsing frequencies. PIV imaging of the associated isothermal fields show the amplification in flame aspect ratio is caused by the narrowing of the inner recirculation zone (IRZ). The Rayleigh criterion (R) is used to assess the potential for instability of specific perturbation configurations and is found to be a good predictor of unstable modes. Phase conditioned analysis of the flame dynamics yield additional criteria in highly responsive modes to include the effective amplitude of velocity oscillations induced by the acoustic pulsing. Highly amplified responses were observed in pulsed flame configurations with Strouhal numbers (St = fpUavg/dm) in the 1–3.5 range. Heat release to velocity perturbation time delays on the order of the acoustic pulsing period also characterized the highly responsive flames. Finally, wavelet analyses of heat release perturbations indicate sustained low frequency oscillations that become more prominent for low acoustic pulsing frequencies in lean flame configurations.

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Flame Dynamics During Combustion Instability in a High-Pressure, Shear-Coaxial Injector Combustor

Flow Turbulence and Combustion ◽

10.1007/s10494-014-9569-x ◽

2014 ◽

Vol 94 (1) ◽

pp. 237-262 ◽

Cited By ~ 60

Author(s):

S. Srinivasan ◽

R. Ranjan ◽

S. Menon

Keyword(s):

High Pressure ◽

Combustion Instability ◽

Flame Dynamics ◽

Shear Coaxial Injector ◽

Coaxial Injector

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The Effect of Stratification Ratio on the Macrostructure of Stratified Swirl Flames: Experimental and Numerical Study

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-77155 ◽

2018 ◽

Author(s):

Xiao Han ◽

Davide Laera ◽

Aimee S. Morgans ◽

Yuzhen Lin ◽

Chih-Jen Sung

Keyword(s):

Fluid Dynamics ◽

Numerical Study ◽

Large Eddy Simulations ◽

Flame Dynamics ◽

Large Eddy ◽

Swirling Flame ◽

Different Shapes ◽

Flame Quenching ◽

Simulation Results ◽

Good Agreement

The present article reports experimental and numerical analyses of the macrostructures featured by a stratified swirling flame for varying stratification ratio (SR). The studies are performed with the Beihang Axial Swirler Independently-Stratified (BASIS) burner, a novel double-swirled full-scale burner developed at Beihang University. Experimentally, it is found that depending on the ratio between the equivalence ratios of the methane-air mixtures from the two swirlers, the flame stabilizes with three different shapes: attached V–flame, attached stratified flame and lifted flame. In order to better understand the mechanisms leading to the three macrostructures, large eddy simulations (LES) simulations are performed via the open source Computational Fluid Dynamics software OpenFOAM using the incompressible solver Reacting Foam. Changing the SR, simulation results show good agreement with experimentally observed time-averaged flame shapes, demonstrating that the incompressible LES are able to fully characterize the different flame behaviours observed in stratified burners. When the LES account for heat loss from walls, they better capture the experimentally observed flame quenching in the outer shear layer. Finally, insights into the flame dynamics are provided by analysing probes located near the two separate streams.

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Investigation of Flame Dynamics in a V - Flame Combustor During Combustion Instability

ASME 2014 Gas Turbine India Conference ◽

10.1115/gtindia2014-8345 ◽

2014 ◽

Author(s):

R. Vishnu ◽

R. I. Sujith ◽

Preeti Aghalayam

Keyword(s):

Heat Release ◽

Heat Release Rate ◽

Release Rate ◽

Large Amplitude ◽

Gas Turbines ◽

High Speed ◽

Combustion Instability ◽

Flame Dynamics ◽

The Stability ◽

Flame Behavior

Propulsion systems such as gas turbines are susceptible to combustion instability, when operated at lean equivalence ratio [1]. During combustion instability, there is a nonlinear interaction between combustion and acoustics leading to large amplitude acoustic oscillations. These large amplitude oscillations are detrimental to the stability of the combustor and can cause damages to the structural integrity of the combustor, flame flash back or blow off. The main source of nonlinearity is in the heat release rate caused due to the velocity perturbations at the flame holder [2]. The heat release rate fluctuations are due to the variation in the flame surface area. Hence there is a need to understand the flame dynamics that contributes to the heat release rate fluctuations. The present study aims in understanding the stability of a V - flame combustor by varying the flame location inside an acoustic resonator. By varying the flame location the instability regimes of the combustor are identified. At the flame locations where the system exhibits combustion instability, acoustic pressure oscillations are acquired simultaneously with high speed images of the flame front fluctuations so that a correlation can be made between them. Tools from dynamical systems theory are applied to the pressure signal to quantify different dynamical states of the system during combustion instability. Moreover the flame dynamics at each dynamical state are investigated. It is observed that combustion instability is characterized by interesting dynamical states such as frequency locked state, quasi-periodic oscillations, period 3 oscillations and chaotic oscillations. High speed imaging of the flame reveals different interesting patterns of flame behavior during combustion instability. Flame wrinkling, roll up of flame elements, separation as islands of the flame elements and mutual annihilation of flame elements were some of the interesting flame behavior observed. This study helps in understanding the role of nonlinear heat release rate mechanism in establishing different dynamical states during combustion instability.

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Detection and Analysis of Combustion Instability From Hi-Speed Flame Images Using Dynamic Mode Decomposition

Volume 1: Advances in Control Design Methods, Nonlinear and Optimal Control, Robotics, and Wind Energy Systems; Aerospace Applications; Assistive and Rehabilitation Robotics; Assistive Robotics; Battery and Oil and Gas Systems; Bioengineering Applications; Biomedical and Neural Systems Modeling, Diagnostics and Healthcare; Control and Monitoring of Vibratory Systems; Diagnostics and Detection; Energy Harvesting; Estimation and Identification; Fuel Cells/Energy Storage; Intelligent Transportation ◽

10.1115/dscc2016-9907 ◽

2016 ◽

Cited By ~ 2

Author(s):

Sambuddha Ghosal ◽

Vikram Ramanan ◽

Soumalya Sarkar ◽

Satyanarayanan R. Chakravarthy ◽

Soumik Sarkar

Keyword(s):

Gas Turbines ◽

Internal Combustion Engines ◽

Structural Integrity ◽

Combustion Instability ◽

Complex Problem ◽

Operating Conditions ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Flame Dynamics ◽

Mode Decomposition

Flame dynamics and combustion instability is a complex problem involving different non-linearities. Combustion instability has several detrimental effects on flight-propulsion dynamics and structural integrity of gas turbines and any such spaces where combustion takes places internally, primarily in internal combustion engines. The description of coherent features of fluid flow in such cases is essential to our understanding of the flame dynamics and propagation processes. A method that is able to extract dynamic information from flow fields that are generated by a direct numerical simulation or visualized in a physical experiment (like in the case discussed in this paper) is Dynamic Mode Decomposition. This paper presents such a feature extraction and stability analysis of hi-speed combustion flames using Dynamic Mode Decomposition and it’s sparsity promoting variant. Extensive experimental data was collected in a swirl-stabilized dump combustor at various operating conditions (e.g. premixing level and flow velocity) for analysing the flame stability conditions.

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The Effect of Stratification Ratio on the Macrostructure of Stratified Swirl Flames: Experimental and Numerical Study

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4040735 ◽

2018 ◽

Vol 140 (12) ◽

Cited By ~ 6

Author(s):

Xiao Han ◽

Davide Laera ◽

Aimee S. Morgans ◽

Yuzhen Lin ◽

Chih-Jen Sung

Keyword(s):

Numerical Study ◽

Large Eddy Simulations ◽

Flame Dynamics ◽

Large Eddy ◽

Swirling Flame ◽

Computational Fluid Dynamics Cfd ◽

Different Shapes ◽

Flame Quenching ◽

Simulation Results ◽

Good Agreement

The present paper reports experimental and numerical analyses of the macrostructures featured by a stratified swirling flame for varying stratification ratio (SR). The studies are performed with the Beihang Axial Swirler Independently Stratified (BASIS) burner, a novel double-swirled full-scale burner developed at Beihang University. Experimentally, it is found that depending on the ratio between the equivalence ratios of the methane–air mixtures from the two swirlers, the flame stabilizes with three different shapes: attached V-flame, attached stratified flame, and lifted flame. In order to better understand the mechanisms leading to the three macrostructures, large eddy simulations (LES) are performed via the open-source computational fluid dynamics (CFD) software OpenFOAM using the incompressible solver ReactingFoam. Changing SR, simulation results show good agreement with experimentally observed time-averaged flame shapes, demonstrating that the incompressible LES are able to fully characterize the different flame behaviors observed in stratified burners. When the LES account for heat loss from walls, they better capture the experimentally observed flame quenching in the outer shear layer (OSL). Finally, insights into the flame dynamics are provided by analyzing probes located near the two separate streams.

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