scholarly journals Flame dynamics during intermittency and secondary bifurcation to longitudinal thermoacoustic instability in a swirl-stabilized annular combustor

2020 ◽  
Author(s):  
Amitesh Roy ◽  
Samarjeet Singh ◽  
Asalatha Nair ◽  
Swetaprovo Chaudhuri ◽  
R.I. Sujith
Keyword(s):  
Thermoacoustic Instability ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Secondary Bifurcation

Intermittency, Secondary Bifurcation and Mixed Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling

2021 ◽  
Author(s):  
Samarjeet Singh ◽  
Amitesh Roy ◽  
K V Reeja ◽  
Asalatha A. S. Nair ◽  
Swetaprovo Chaudhuri ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Mixed Mode Oscillations ◽  
Annular Combustor ◽  
Secondary Bifurcation

A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine

2020 ◽  
Author(s):  
Matthias Haeringer ◽  
Guillaume J. J. Fournier ◽  
Max Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Wave Theory ◽  
Bloch Wave ◽  
Reflection Coefficients ◽  
Test Rig ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Passive Acoustic ◽  
Thermoacoustic Properties ◽  
Dominant Frequencies

Abstract Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.

Lean Blowout Phenomena and Prior Detection of Lean Blowout in a Premixed Model Annular Combustor

2019 ◽  
Author(s):  
Arijit Bhattacharya ◽  
Bikash Gupta ◽  
Satyajit Hansda ◽  
Zohadul Haque ◽  
Ashish Kumar ◽  
...  
Keyword(s):  
Bluff Body ◽  
Nox Reduction ◽  
Marked Change ◽  
Nox Emission ◽  
Thermoacoustic Instability ◽  
Lean Blowout ◽  
Lean Combustion ◽  
Annular Combustor ◽  
Lean Limit ◽  
Lift Off

Abstract Strict emission norms in the last few decades have paved the path for adaptation of new low NoX emission alternatives to power generation and aircraft propulsion. Lean combustion is a very promising and practicable technology for reducing NOX reduction and also have very high fuel efficiency. However, lean combustion technology suffers from inherent combustion instabilities that are manifested under different conditions, most importantly, thermoacoustic instability and lean blowout. Lean blowout occurs when a gas turbine combustor operating close to lean limit, for lowest NoX emission, faces abrupt changes in fuel homogeneity, quality or flow rate. While many work have been done in thermo-acoustic instability and flame propagation in annular combustors, studies in lean blowout in annular combustors are very limited. The lean limit of combustors are not fixed and is dependent on fuel characteristics and operating condition including environmental effects. So accurate online prediction of lean limit is very important to keep the combustors operating safely near lean limit. Recent works have demonstrated that single burner combustors leave out a significant amounts of physics including interaction of flames from different burners prior to blowout. In this work, a stepped down swirl and bluff body stabilized annular combustor in CB configuration (having chamber and burner), is used as experimental test rig having 4 number of identical burners. Video and heat release data are taken at different conditions as lean blowout is approached. Frequent attachment and reattachment of the flames prior to lift off was seen. As lean blowout is approached, inherent subtle differences in the different burners get amplified when flame becomes sufficiently weak and flame symmetry is broken. As air fuel mixture is made gradually leaner, one by one the flames from different burners elongates although remains partially attached to burner. Further lowering the equivalence ratio results in lift off and merging of the flame fronts of different burners. Three pixel averaged color ratios are extracted from still camera RGB images as flame stability indicators which are, red by blue, red by green and blue by green. The parameters show marked change at the point of lift off as well as at the lean blowout point.

scholarly journals Multiphase Flow Large-Eddy Simulation Study of the Fuel Split Effects on Combustion Instabilities in an Ultra-Low-NOx Annular Combustor

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
M. Bauerheim ◽  
T. Jaravel ◽  
L. Esclapez ◽  
E. Riber ◽  
L. Y. M. Gicquel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Multiphase Flow ◽  
Analytical Model ◽  
Vortex Shedding ◽  
Gaseous Fuel ◽  
Combustion Instabilities ◽  
Eddy Simulation ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Annular Combustor

This paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: (1) a gaseous type in the multipoint zone (MPZ) where acoustics generates vortex shedding, which then wrinkle the flame front, and (2) a multiphase flow type in the pilot zone (PZ) where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the PZ and mechanism 2) to assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using an analytical model validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations in the PZ, which strongly depend on the fuel split parameter. However, the correlation between acoustics and the global (pilot + multipoint) heat release fluctuations highlights no dependency on the fuel split staging. It suggests that vortex shedding in the MPZ, almost not depending on the fuel split, is the main feature controlling the flame dynamics for this engine.

Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling

2020 ◽  
Author(s):  
Samarjeet Singh ◽  
Amitesh Roy ◽  
Reeja K. V. ◽  
Asalatha Nair ◽  
Swetaprovo Chaudhuri ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Equivalence Ratio ◽  
High Amplitude ◽  
The State ◽  
Turbulent Flames ◽  
Bulk Velocity ◽  
Thermoacoustic Instability ◽  
Mixed Mode Oscillations ◽  
Annular Combustor ◽  
Low Amplitude

Abstract We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.

A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine

2020 ◽  
Author(s):  
Matthias Haeringer ◽  
Guillaume Jean Jacques Fournier ◽  
Maximilian Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Wave Theory ◽  
Bloch Wave ◽  
Reflection Coefficients ◽  
Test Rig ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Passive Acoustic ◽  
Thermoacoustic Properties ◽  
Dominant Frequencies

Abstract Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.

Experimental and Numerical Characterization of a Novel Natural Gas Low NOx Burner in Gas Turbine Realistic Environment

2020 ◽  
Author(s):  
Matteo Cerutti ◽  
Pier Carlo Nassini ◽  
Daniele Pampaloni ◽  
Antonio Andreini
Keyword(s):  
Gas Turbine ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
The Novel ◽  
Thermoacoustic Instability ◽  
Numerical Characterization ◽  
Annular Combustor ◽  
Development Phases ◽  
Reduced Scale

Abstract A fundamental milestone in the development of a low NOx burner technology is the demonstration of its capabilities in realistic environment. This is especially true for the novel burner subject of this paper, which has been extensively characterized throughout single burner scale experiments. An exhaustive description of the early development phases of the novel burner has been provided by authors in recently published works. The most promising geometry was selected for the assessment in real combustor arrangement, consisting of a full-scale annular combustor test rig. This paper reports the main results of such an assessment. Pollutant emissions and pressure pulsations have been measured at gas turbine relevant operating conditions. Moreover, dedicated blow-out tests have been performed to obtain the extinction equivalence ratio at both ambient and pressurized conditions, as done during the past single burner rig campaign. Basically, an adequate set of data has been gathered, allowing a direct comparison between full-annular and reduced-scale tests. A general alignment of behaviour has been observed, as both low NOx capability and blow-out characteristics of full-annular arrangement turned out to be substantially unchanged with respect to single burner. Nevertheless, some discrepancies in magnitude have been highlighted and discussed. Details have been given involving deeper numerical analysis by means of a dedicated model developed by the authors in previous works. Indeed, improvement to the model has been introduced in the context of this paper to overcome some limitations arisen in predicting emissions. Finally, a preliminary stability analysis has been carried out, with the aim to describe the onset of thermoacoustic instability tendency as observed in the full-annular tests.

Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling

2020 ◽  
Author(s):  
Samarjeet Singh ◽  
Amitesh Roy ◽  
K. V. Reeja ◽  
Asalatha Nair ◽  
Swetaprovo Chaudhuri ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Equivalence Ratio ◽  
High Amplitude ◽  
The State ◽  
Turbulent Flames ◽  
Bulk Velocity ◽  
Thermoacoustic Instability ◽  
Mixed Mode Oscillations ◽  
Annular Combustor ◽  
Low Amplitude

Abstract We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.

Experimental and Numerical Characterization of a Novel Natural Gas Low NOx Burner in Gas Turbine Realistic Environment

2020 ◽  
Author(s):  
Matteo Cerutti ◽  
Pier Carlo Nassini ◽  
Daniele Pampaloni ◽  
Antonio Andreini
Keyword(s):  
Gas Turbine ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
The Novel ◽  
Thermoacoustic Instability ◽  
Numerical Characterization ◽  
Annular Combustor ◽  
Development Phases ◽  
Reduced Scale

Abstract A fundamental milestone in the development of a low NOx burner technology is the demonstration of its capabilities in realistic environment. This is especially true for the novel burner subject of this paper, which has been extensively characterized throughout single burner scale experiments. The most promising geometry from the early development phases was selected for the assessment in realistic environment, consisting of a full-scale annular combustor test rig. This paper reports the main results of the assessment. Pollutant emissions and pressure pulsations have been measured at gas turbine relevant operating conditions. Moreover, dedicated blow-out tests have been performed to obtain the extinction equivalence ratio at both ambient and pressurized conditions, as done during the previous campaign. Basically, an adequate set of data has been gathered, allowing a direct comparison between full-annular and reduced-scale tests. A general alignment of behaviour has been observed, as both low NOx capability and blow-out characteristics of full-annular arrangement turned out to be substantially unchanged with respect to single burner. Nevertheless, some discrepancies in magnitude have been highlighted and discussed. Details have been given involving deeper numerical analysis by means of a dedicated model developed by the authors in previous works. Indeed, improvement to the model has been introduced in the context of this paper to overcome some limitations arisen in predicting emissions. Finally, a preliminary stability analysis has been carried out, with the aim to describe the onset of thermoacoustic instability tendency as observed in the full-annular tests.

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