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Nicholas Syred - One of the best experts on this subject based on the ideXlab platform.
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CFD predictions of Swirl Burner aerodynamics with variable outlet configurations
International Journal of Energy Technology, 2019Co-Authors: Hesham Baej, Nicholas Syred, Agustin Valera Medina, Richard Marsh, Philip John BowenAbstract:Swirl stabilised combustion is one of the most widely used techniques for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The Swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of Swirl, Burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. Therefore, in this paper Swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic Swirl Burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using several gaseous blends at a constant power output. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by the blend and infer that it is governed by both the shear layer surrounding the Central Recirculation Zones (CRZ) and the gas composition.
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Central recirculation zone analysis in an unconfined tangential Swirl Burner with varying degrees of premixing
Experiments in Fluids, 2011Co-Authors: A. Valera-medina, Nicholas Syred, A. GriffithsAbstract:Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the Swirl Burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of Swirl (Swirl number), Burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high Swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of Swirl number in a generic Swirl Burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion.
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Central recirculation zone analysis in an unconfined tangential Swirl Burner with varying degrees of premixing
Experiments in Fluids, 2011Co-Authors: A. Valera-medina, Nicholas Syred, A. GriffithsAbstract:Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the Swirl Burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of Swirl (Swirl number), Burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high Swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of Swirl number in a generic Swirl Burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion.
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Flashback avoidance analysis using geometrical constrictions in a tangential Swirl Burner
2009Co-Authors: Agustin Valera Medina, Mohammed Abdulsada, Anthony John Griffiths, Nicholas SyredAbstract:The flashback analysis in Gas Turbines for Power Generation has been of great concern for manufacturers and researchers in the last decade. This is due to the increased interest in using biofuels and enriched hydrogen combustibles for emission reduction and economical alternatives to fossils. This paper analyses experimentally and numerically the phenomenon in a Tangential Swirl Burner under different conditions in order to increase the understanding of the phenomenon to reduce its impacts in real gas turbines.
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Visualisation of isothermal large coherent structures in a Swirl Burner
Combustion and Flame, 2009Co-Authors: A. Valera-medina, Nicholas Syred, Anthony John GriffithsAbstract:Lean premixed combustion using Swirl flame stabilisation is widespread amongst gas turbine manufacturers. The use of Swirl mixing and flame stabilisation is also prevalent in many other non-premixed systems. Problems that emerge include loss of stabilisation as a function of combustor geometry and thermo-acoustic instabilities. Coherent structures and their relationship with combustion processes have been a concern for decades due to their complex nature. This paper thus adopts an experimental approach to characterise large coherent structures in Swirl Burners under isothermal conditions so as to reveal the effects of Swirl in a number of geometries and cold flow patterns that are relevant in combustion. Aided by techniques such as Hot Wire Anemometry, High Speed Photography and Particle Image Velocimetry, the recognition of several structures was achieved in a 100 kW Swirl Burner model. Several varied, interacting, structures developed in the field as a consequence of the configurations used. New structures never observed before were identified, the results not only showing the existence of very well defined large structures, but also their dependency on geometrical and flow parameters. The PVC is confirmed to be a semi-helical structure, contrary to previous simulations performed on the system. The appearance of secondary recirculation zones and suppression of the vortical core as a consequence of geometrical constrictions are presented as a mechanism of flow control. The asymmetry of the Central Recirculation Zone in cold flows is observed in all the experiments, with its elongation dependent on Re and Swirl number used.
Timothy O'doherty - One of the best experts on this subject based on the ideXlab platform.
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Dynamic modelling of low frequency oscillations in Swirl Burner/furnace systems using artificial neural networks
Journal of the Energy Institute, 2006Co-Authors: Y. Xue, Nicholas Syred, V. M. Rodriguez-martinez, Timothy O'dohertyAbstract:AbstractThe present paper is concerned with modelling techniques for combustion excited oscillations in Swirl Burner/furnace systems (SBF) for control strategy development. Artificial neural networks are used to model the combustion dynamics in an SBF which can be made to oscillate under various conditions. A methodology for building system models is proposed where dynamic flowrate measurements of gas and air are absent, the inputs being pressure time records, measurements of mean gas and air flowrates and geometry of the furnace. The modelling has two objectives: one is to model the system fluctuating pressure frequencies and rms amplitude, which can then be used to build a core stimulation model and the other to model the time domain dynamic response to pressure oscillation. Experiments were undertaken on a 100 kW Swirl Burner/furnace systems (SBF) test rig. This system could be made to oscillate regularly by parametric changes such as mean equivalence ratio, mean gas and air flowrates and small geometr...
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THE EFFECT OF COMBUSTION INSTABILITY ON RECIRCULATION ZONES IN A Swirl Burner/FURNACE
42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004Co-Authors: James R. Dawson, Nicholas Syred, V. M. Rodriguez Martinez, Timothy O'dohertyAbstract:The effect of changing the expansion plane geometry on combustion instability is discussed based on pressure, volumetric flowrates and global heat release measurements carried out in a Swirl Burner/furnace under combustion instability. The original expansion plane is modified by inserting a divergent exit in an effort to enhance the stability of the recirculation zones and passively damp the amplitude of the pressure oscillations. Results plotting the rms pressure amplitudes, prms, as a function of equivalence ratio, o, show that the modified expansion geometry reduced prms by as much as 40% between o = 0.6 to 0.7 and up to 50% between o = 0.75 to 0.85. The relative volumetric flowrates between the recirculation zones and the Swirling jet are analysed over the limit cycle and show that significant variations in the structure of the recirculation zones occur over the limit-cycle. It is found that the reductions in prms and velocity amplitude are achieved by better stability of the recirculation zones and better preservation of their volumetric flowrates for the low-pressure part of the cycle. Evaluation of the Rayleigh index showed that the driving and damping regions were located near the proximity of the Burner and downstream of the breakdown zone respectively. The passive of control of the recirculation zones is discussed and illustrates a simple, but effective technique that can be implemented alongside other control strategies.
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The Effect of the Precessing Vortex Core on Combustion in a Swirl Burner
Combustion Science and Technology, 1997Co-Authors: Nicholas Syred, Timothy O'doherty, W. Fick, A. J. GriffithsAbstract:Abstract This paper examines the fundamental characteristics of a 2 MW Swirl Burner/furnace system and in particular the excitation of the Precessing Vortex Core (PVC) in diffusion controlled combustion with, natural gas being introduced axially on the axis of symmetry. Previous studies have indicated that under such conditions the PVC is virtually undetectable. The phenomena was investigated via phase averaged LDA and fine wire thermocouple measurements. The PVC influence is shown to extend over virtually all the furnace volume. A processing jet like structure of high velocity is created in which combustion is limited and temperatures are low. This region is responsible for the very high rates of mixing found in such systems. Clear relevance to practical industrial system is indicated.
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Studies of helmholtz resonance in a Swirl Burner/furnace system
Symposium (International) on Combustion, 1996Co-Authors: Daniel Froud, A. J. Beale, Timothy O'doherty, Nicholas SyredAbstract:This paper describes and analyzes the combustion-excited Helmholtz resonance in a Swirl Burner/furnace system. Preliminary work showed the importance of variables such as air/fuel ratio, mode of fuel entry, and length of exhaust pipe attached to the exit of the furnace. Conditions were chosen (50% axial, 50% premixed natural gas and air, 600-mm-long exit pipe, air/fuel ratio=1.53) that gave a clean, near sinusoidal pressure signal at the furnace exit. This signal was used as a trigger to enable phase-averaged axial and tangential velocities as well as temperatures to be taken throughout the furnace and into the exit pipe. The results show that a lifted flame core region exists over all of the oscillation cycle. Combustion excitation via the Rayleigh criteria comes via a periodic combustion wave of annular form located next to the furnace wall. The minimum pressure of the resonance causes a large inflow into the furnace with well-known Swirltype flow patterns, which extinguishes the annular wall flame. The central flame core boundary is located in a low-velocity region between the forward and reverse flow regions. Conversely, the peak resonant pressure virtually stops the inflow into the furnace from the Burner and allows the annular wall flame to propagate backward into the furnace. Complex coherent structures in the tangential radial direction are formed close to the junction of the Swirl Burner and the furnace. The influence of the precessing vortex core (PVC) in the Swirl Burner exhaust in setting up the resonance seems to be small; however, it does appear to further excite the resonance to higher amplitudes when its frequency is close to that of the Helmholtz oscillation.
Simone Hochgreb - One of the best experts on this subject based on the ideXlab platform.
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effect of mixture flow stratification on premixed flame structure and emissions under counter rotating Swirl Burner configuration
Applied Thermal Engineering, 2016Co-Authors: Cheng Tung Chong, Su Shiung Lam, Simone HochgrebAbstract:An investigation of the flame structure and emission performance of stratified Swirl methane/air flames was performed by using a double-annulus counter-rotating premixed Swirl Burner. Stratification of the flow and mixtures were established by varying the bulk air flow rates and mixture equivalence ratios between the inner and outer annuli. Two distinct flame fronts were stabilised at the Burner outlet, separated by a shear layer due to velocity differences. Higher Swirl flow in the inner annulus generates an elongated and enlarged area of flame reaction zone due to increased flame intensity, as the flame shape is strongly dependent on the velocity magnitude exiting the annulus. Mixture and flow stratification affect local emissions. A richer mixture stratification within the inner channel at 70:30 flow split results in 91% and 49% higher emission rates of NO and CO respectively compared to premixed arrangement, in spite generally aiding flame stability. Enrichment of the outer annulus at 70:30 split flow shows only slightly higher levels of NO and CO emissions by 3% and 9% respectively compared to a homogenous mixture.
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temperature measurements of the bluff body surface of a Swirl Burner using phosphor thermometry
Combustion and Flame, 2014Co-Authors: Matthias Euler, Ruigang Zhou, Simone Hochgreb, A DreizlerAbstract:Abstract Flames are often stabilised on bluff-bodies, yet their surface temperatures are rarely measured. This paper presents temperature measurements for the bluff body surface of the Cambridge/Sandia Stratified Swirl Burner. The flame is stabilized by a bluff body, designed to provide a series of turbulent premixed and stratified methane/air flames with a variable degree of Swirl and stratification. Recently, modellers have raised concerns about the role of surface temperature on the resulting gas temperatures and the overall heat loss of the Burner. Laser-induced phosphorescence is used to measure surface temperatures, with Mg4GeO6F:Mn as the excitation phosphor, creating a spatially resolved temperature map. Results show that the temperature of the bluff body is in the range 550–900 K for different operating conditions. The temperature distribution is strongly correlated with the degree of Swirl and local equivalence ratio, reflecting the temperature distribution obtained in the gas phase. The overall heat loss represents only a small fraction (
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flow field results of the cambridge stratified Swirl Burner using laser doppler anemometer
2012Co-Authors: Ruigang Zhou, Mark Sweeney, Simone HochgrebAbstract:A series of flow fields generated by a turbulent methane/air stratified Swirl Burner are investigated using laser Doppler anemometer (LDA) to obtain the velocities in axial, radial and tangential directions. All mean and RMS of the LDA velocity results are supplied along with a report describing the experimental methodology, data processing routines and the data format.
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Flow field of a model gas turbine Swirl Burner
Advanced Materials Research, 2012Co-Authors: Cheng Tung Chong, Simone HochgrebAbstract:The flow field of a lab-scale model gas turbine Swirl Burner was characterised using particle imaging velocimetry (PIV) at atmospheric condition. The Swirl Burner consists of an axial Swirler, a twin-fluid atomizer and a quartz tube as combustor wall. The main non-reacting Swirling air flow without spray was compared to Swirl flow with spray under unconfined and enclosed conditions. The introduction of liquid fuel spray changes the flow field of the main Swirling air flow at the Burner outlet where the radial velocity components are enhanced. Under reacting conditions, the enclosure generates a corner recirculation zone that intensifies the strength of the radial velocity. Comparison of the flow fields with a spray flame using diesel and palm biodiesel shows very similar flow fields. The flow field data can be used as validation target for Swirl flame modelling.
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Technical Drawings of Cambridge Stratified Swirl Burner (SwB)
2008Co-Authors: Mark Sweeney, Robert S. Barlow, Simone HochgrebAbstract:Technical drawings (plan, elevation etc) of components in the Cambridge Stratified Swirl Burner. All images are to scale
A. Valera-medina - One of the best experts on this subject based on the ideXlab platform.
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Central recirculation zone analysis in an unconfined tangential Swirl Burner with varying degrees of premixing
Experiments in Fluids, 2011Co-Authors: A. Valera-medina, Nicholas Syred, A. GriffithsAbstract:Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the Swirl Burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of Swirl (Swirl number), Burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high Swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of Swirl number in a generic Swirl Burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion.
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Central recirculation zone analysis in an unconfined tangential Swirl Burner with varying degrees of premixing
Experiments in Fluids, 2011Co-Authors: A. Valera-medina, Nicholas Syred, A. GriffithsAbstract:Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving the ability to produce low NOx systems coupled with wide stability limits. The common element is the Swirl Burner, which depends on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time dependent. The characteristics of the CRZ depend very strongly on the level of Swirl (Swirl number), Burner configuration, type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success when compared to experimental results, the models still have difficulties at medium to high Swirl levels, with complex geometries and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under varied combustion conditions with different geometries and some variation of Swirl number in a generic Swirl Burner. CRZ behaviour has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than pure diffusive combustion.
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Visualisation of isothermal large coherent structures in a Swirl Burner
Combustion and Flame, 2009Co-Authors: A. Valera-medina, Nicholas Syred, Anthony John GriffithsAbstract:Lean premixed combustion using Swirl flame stabilisation is widespread amongst gas turbine manufacturers. The use of Swirl mixing and flame stabilisation is also prevalent in many other non-premixed systems. Problems that emerge include loss of stabilisation as a function of combustor geometry and thermo-acoustic instabilities. Coherent structures and their relationship with combustion processes have been a concern for decades due to their complex nature. This paper thus adopts an experimental approach to characterise large coherent structures in Swirl Burners under isothermal conditions so as to reveal the effects of Swirl in a number of geometries and cold flow patterns that are relevant in combustion. Aided by techniques such as Hot Wire Anemometry, High Speed Photography and Particle Image Velocimetry, the recognition of several structures was achieved in a 100 kW Swirl Burner model. Several varied, interacting, structures developed in the field as a consequence of the configurations used. New structures never observed before were identified, the results not only showing the existence of very well defined large structures, but also their dependency on geometrical and flow parameters. The PVC is confirmed to be a semi-helical structure, contrary to previous simulations performed on the system. The appearance of secondary recirculation zones and suppression of the vortical core as a consequence of geometrical constrictions are presented as a mechanism of flow control. The asymmetry of the Central Recirculation Zone in cold flows is observed in all the experiments, with its elongation dependent on Re and Swirl number used.
Wolfgang Polifke - One of the best experts on this subject based on the ideXlab platform.
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identification of flame transfer functions from les of a premixed Swirl Burner
Proceedings of ASME Turbo Expo 2010: Power for Land Sea and Air GT 2010, 2010Co-Authors: Luis Tay Wo Chong, Thomas Komarek, R Kaess, Stephan Fo Ller, Wolfgang PolifkeAbstract:Large eddy simulations of compressible, turbulent, reacting flow were carried out in order to identify the Flame Transfer Function (FTF) of a premixed Swirl Burner at different power ratings. The Thickened Flame model with one step kinetics was used to model combustion. Time-averaged simulation results for inert and reacting flow cases were compared with experimental data for velocity and heat release distribution with good agreement. Heat losses at the combustor walls were found to have a strong influence on computed flame shapes and spatial distributions of heat release. For identification of the FTF with correlation analysis, broadband excitation was imposed at the inlet. At low power rating (30 kW), measured and computed FTFs agree very well at low frequencies (corresponding to Strouhal numbers St < 4), showing a pronounced maximum of the gain at St ≈ 2. At higher frequencies, where the flame response weakens, the agreement between experiment and computation deteriorates, presumably due to decreasing signal-to-noise ratio. At higher thermal power (50 kW), a high-frequency instability developed during the simulation runs, resulting in poor overall signal-to-noise ratio and thus to unsatisfactory prediction of the gain of the flame transfer function. The phase of the FTF, on the other hand, was predicted with good accuracy up to St < 5. An analytical expression for the FTF, which models the flame dynamics as a superposition of time-delayed responses to perturbations of mass flow rate and Swirl number, respectively, was found to match the experimental results.Copyright © 2010 by ASME
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Scattering and generation of acoustic energy by a premix Swirl Burner
Int’l Gas Turbine and Aeroengine Congress & Exposition. May, 2007Co-Authors: Alexander Gentemann, Wolfgang PolifkeAbstract:Thescattering and generation of acoustic energy by a premix SwirlBurner is scrutinized. The analysis is formulated in terms ofthe scattering matrix of the Burner, determined by a combinationof computational fluid dynamics and system identification as well asexperiment supplemented with simple analytical models for flame frequency responseand Burner transfer matrix. Remarkably, it is found that ina narrow range of frequencies, incoming acoustic waves are amplifiedstrongly by the unsteady heat release, i.e. acoustic energy isgenerated. Although the computational and experimental data were obtained forone specific Swirl Burner design, further analysis suggests that suchbehavior should be common for many Burner designs. Consequences forthermo-acoustic stability as well as Burner and combustor design strategiesare discussed. ©2007 ASME
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a model for the thermoacoustic response of a premixed Swirl Burner part i acoustic aspects
Combustion Science and Technology, 2004Co-Authors: C.j. Lawn, S Evesque, Wolfgang PolifkeAbstract:Results from previous measurements on a small laboratory Swirl Burner undergoing self-excited acoustic oscillations with premixtures of either CH4 or C3H8 are summarized. The measurements of acoustic pressure and the distribution of chemiluminescent emission were used to deduce semi-empirical descriptions of the flame response functions, and these are used here in conjunction with a validated model for the acoustics of the premixture supply system, Burner, and combustion chamber to reproduce the excitation frequencies and to deduce the required amplitudes of the flame response function. Variations of the Burner flow rate and the equivalence ratio are examined, as is the sensitivity of the results to the acoustic and flame parameters. The results are of considerable relevance to the response of industrial gas-turbine combustion systems, and the calculations lay the foundations for the fundamental model of the flame response that is derived in Part II.
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a model for the thermoacoustic response of a premixed Swirl Burner part ii the flame response
Combustion Science and Technology, 2004Co-Authors: C.j. Lawn, Wolfgang PolifkeAbstract:A comprehensive model for the response of a premixed flame to acoustic velocity fluctuations is developed and applied to the same small laboratory Swirl Burner as was treated in Part I, using the validated model for the acoustics of the system. A number of possible mechanisms of acoustic interactions with the flame are reviewed, and the three judged to be the most important for this application are quantified on a consistent basis. The three mechanisms are those due to the direct influence of the velocity and turbulence, to coherent vortices shed from the Burner exit, and to equivalence ratio fluctuations. The time-averaged position of the flame front at which most of the excitation takes place is identified from the observations, and the direction of the incident flow is deduced. The overall response to planar acoustic waves through the Burner is then worked out. Comparison with experimental data for a wide range of conditions shows that the major trends in frequency of self-excitation are correctly pred...
