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Author: Daniel Bernier
Publisher:
ISBN:
Category :
Languages : fr
Pages : 263
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Book Description
Les instabilités de combustion apparaissent souvent dans les turbines à gaz et engendrent des dommages importants. Le travail mené ici consiste en l'étude du contrôle actif de ces instabilités sur un foyer prémélangé prévaporisé. Une telle étude constitue une étape de base pour l'application du contrôle actif dans les turbines à gaz. Après une analyse détaillée des mécanismes impliqués dans les instabilités de combustion, différents systèmes actionneurs modulant une partie du débit d'air sont testés pour leur application au contrôle actif. Le système le plus efficace agit à la base du brouillard de combustible et permet un contrôle des instabilités en configuration co-rotative des vrilles de l'injecteur. Par contre, le système perd en efficacité à des fréquences supérieures a 300 Hz en configuration contra-rotative. L'actionneur est ensuite utilisé pour évaluer quatre stratégies de contrôle. On considère d'abord une boucle ouverte (injection de bruit blanc) et une boucle fermée élémentaire (ligne à retard). On envisage ensuite deux contrôleurs adaptatifs. Le premier nécessite une identification préalable du comportement du système. Le second réalise cette identification simultanément au contrôle. Dans le foyer étudié, le contrôle en boucle ouverte permet une réduction supérieure à 60% du niveau d'instabilité sans risque de divergence du processus. Les plus fortes réductions sont obtenues avec l'algorithme auto-adaptatif et atteignent 70% du niveau d'instabilité. Dans l'ensemble des stratégies de contrôle, la réduction des instabilités est obtenue avec une modulation de 3% du débit d'air global. Les performances du contrôleur sont principalement limitées par le niveau de modulation obtenu avec l'actionneur et sa bande-passante. La synthèse des stratégies de contrôle permet une discussion sur leur complexité technologique au regard d'une application industrielle.
Author: Daniel Bernier
Publisher:
ISBN:
Category :
Languages : fr
Pages : 263
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Book Description
Les instabilités de combustion apparaissent souvent dans les turbines à gaz et engendrent des dommages importants. Le travail mené ici consiste en l'étude du contrôle actif de ces instabilités sur un foyer prémélangé prévaporisé. Une telle étude constitue une étape de base pour l'application du contrôle actif dans les turbines à gaz. Après une analyse détaillée des mécanismes impliqués dans les instabilités de combustion, différents systèmes actionneurs modulant une partie du débit d'air sont testés pour leur application au contrôle actif. Le système le plus efficace agit à la base du brouillard de combustible et permet un contrôle des instabilités en configuration co-rotative des vrilles de l'injecteur. Par contre, le système perd en efficacité à des fréquences supérieures a 300 Hz en configuration contra-rotative. L'actionneur est ensuite utilisé pour évaluer quatre stratégies de contrôle. On considère d'abord une boucle ouverte (injection de bruit blanc) et une boucle fermée élémentaire (ligne à retard). On envisage ensuite deux contrôleurs adaptatifs. Le premier nécessite une identification préalable du comportement du système. Le second réalise cette identification simultanément au contrôle. Dans le foyer étudié, le contrôle en boucle ouverte permet une réduction supérieure à 60% du niveau d'instabilité sans risque de divergence du processus. Les plus fortes réductions sont obtenues avec l'algorithme auto-adaptatif et atteignent 70% du niveau d'instabilité. Dans l'ensemble des stratégies de contrôle, la réduction des instabilités est obtenue avec une modulation de 3% du débit d'air global. Les performances du contrôleur sont principalement limitées par le niveau de modulation obtenu avec l'actionneur et sa bande-passante. La synthèse des stratégies de contrôle permet une discussion sur leur complexité technologique au regard d'une application industrielle.
Author: Nicolas Robart
Publisher:
ISBN:
Category :
Languages : fr
Pages : 158
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Book Description
Les instabilités de combustion sont des phénomènes néfastes dans les turbines à gaz. Elles sont la conséquence d'un couplage entre la réaction chimique et l'acoustique de la chambre de combustion. Une voie pour lutter contre ces instabilités est le contrôle actif de la combustion. La spécificité de ce travail vient de la complexité de l'écoulement diphasique étudié. Cet écoulement est produit par un injecteur de turboréacteur de géométrie industrielle qui forme un jet d'air vrillé axisymétrique au centre duquel sont injectées des gouttelettes de carburant. La principale tâche consiste à développer et tester des actionneurs agissant sur le mélange. Les actionneurs utilisés sont basés sur 4 petits jets d'air à haute vitesse et ont été choisis suite à une étude complète des techniques existantes. Des mesures de granulométrie, de vitesse d'air et des visualisations de répartition spatiale des gouttes ont montré l'influence des actionneurs sur le spray. Parmi les actionneurs développés, certains ont été capable de diminuer la taille des gouttes, de modifier la répartition spatiale des gouttes, et de modifier le champ aérodynamique dans l'injecteur. Ces actionneurs ont été associés à une vanne haute fréquence permettant de pulser l'air jusqu'à plus de 400 Hz. Les actionneurs les plus efficaces sur le mélange ont été testés sur un banc expérimental avec combustion. Ils ont permis d'exciter la flamme à des fréquences de l'ordre des fréquences naturellement instables (de 350 à 450 Hz) du brûleur, ce qui laisse envisager la faisabilité du contrôle en boucle fermée à ces fréquences. Une autre voie a été explorée, elle consiste à alimenter les actionneurs en continu et observer si les effets sur le mélange suffisent à modifier la stabilité de la flamme. Cette voie a permis de lutter à certains régimes contre les instabilités, et plus systématiquement contre le "flashback". Améliorer ces résultats nécessite d'utiliser des stratégies de contrôle en boucle fermée.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Author: C. A. Jacobson
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
This paper details the development of a thermoacoustic model and associated dynamic analysis. The model describes the results obtained in a gas fueled experimental combustion program carried out at UTRC. The contents of the paper are (a) the development of a thermoacoustic model composed of acoustic and heat release components, (b) the dynamic analysis of the resulting non-linear model using harmonic balance methods to compute linear stability boundaries and the amplitudes of oscillations and (c) the calibration of the model to experimental data.
Author: Andrzej Banaszuk
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
We present results of experiment with two distinct extremum-seeking adaptive algorithms for control of combustion instability suitable for reduction of acoustic pressure oscillations in gas turbine over large range of operating conditions. The algorithms consists of a frequency tracking Extended Kalman Filter to determine the in-phase component, the quadrature component, and the magnitude of the acoustic mode of interest, and a phase shifting controller with the controller phase tuned using an extremum-seeking algorithms. The algorithms are also applicable for control of oscillations of systems whose oscillation frequency and optimal control phase shift depends on operating conditions, and which are driven by strong broad-band disturbance. The algorithms have been tested in combustion experiments involving full-scale engine hardware and during simulated fast engine transients.
Author: J. Hermann
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
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Book Description
Reducing the output of NOx pollutants and enhancing efficiency are the two major aims pursued by developers of modern gas turbines. In order to achieve them. lean premix combustion is preferred turbine inlet temperatures and thus power densities within the combustion chamber system being continuously increased to augment efficiency. Due to this fact. the tendency of modern combustion systems to develop so-called self- excited combustion oscillations keeps increasing. After briefly discussing the oscillation problems encountered with the annular combustion chamber of a Siemens type V94.3A stationary gas turbine. particular attention will be paid to suppressing these oscillations by passive and active means. The passive measures presented. i.e. extending the burner nozzle were intended to detune the combustion system by prolonging the time lag required by the combustible mixture exiting the burner outlet to reach the combustion zone Moreover. to suppress periodic vortex shedding. another possible cause for combustion instabilities. those extensions were inclined in a certain angle with respect to the main flow direction. To prevent the in-phase lock of all 24 burners promoting the excitation of any azimuthal mode the burners were selected to have different time lags and were arranged asymmetrically within the annular combustion chamber. In addition to these passive measures, a multi-channel Active Instability Control (AIC) system was implemented to achieve further damping. With the AIC system presented. any homer oscillations occurring are measured by p-ressure sensors their signals are processed by means of a multi-channel controller and then transmitted to actuators designed to damp down combustion oscillations. The points of intervention selected to do so were the gas supplies of the pilot flames.
Author: James Fayiah Willie
Publisher: Cuvillier Verlag
ISBN: 3736940017
Category : Technology & Engineering
Languages : en
Pages : 186
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Book Description
The main objective of this thesis is to analyze combustion instabilities in a matrix burner. The various tools that exist for analyzing thermoacoustic instabilities are applied to the matrix burner with multiple flames. The principal goals are to determine the primary causes of combustion instabilities in the burner and to explore ways of controlling such instabilities in order to prevent damage to the burner. To achieve these goals, the stability map of the burner obtained from measurements is analyzed. This is followed by the analysis of the aerodynamics of the cold flow using CFD. Results obtained from CFD are validated with PIV and LDA results from measurements. Critical are the centerline axial velocity inside the combustion chamber and the recirculation zones on the walls of the combustion chamber and those between the various slots of the matrix burner. Cold flow simulations are followed by reactive flow simulations for both gaseous and liquid fuels. A detailed atomization model is developed for the liquid fuel case from experimental data. Two combustion models, namely, the combined finite rate/eddy dissipation model and the finite rate chemistry model are compared in the CFD simulations of combustion instabilities and validation with measurements are done. The latter is chosen over the former because it accounts for chemistry and it is not numerically dissipative. Two CFD softwares, Fluent and CFX are also compared to determine which is better at capturing acoustics. System identification using CFD is used to determine the flame transfer function and the acoustic transfer matrix. This is followed by the use of acoustic forcing and fuel modulation on the primary and pilot in order to limit the amplitude of the instabilities inside the matrix burner combustor. The 1D acoustic network is used to determine the longitudinal eigenmodes of the matrix burner. This is followed by the use of 3D finite element method (FEM) and fluid-structure interaction (FSI) to determine whether a coupling exist between the fluid and structure of the matrix burner combustor and vice versa. Finally, Full harmonic analysis is performed for the rectangular combustor and the results obtained are validated with analytical results. This is followed by the 3D structure modal analysis of the full matrix burner test rig.
Author: Michael D. Cornwell
Publisher:
ISBN:
Category :
Languages : en
Pages : 415
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Book Description
Combustion at high pressure in applications such as rocket engines and gas turbine engines commonly experience destructive combustion instabilities. These instabilities results from interactions between combustion heat release, fluid mechanics and acoustics. This research explores the significant affect of unstable fluid mechanics processes in augmenting unstable periodic combustion heat release. The frequency of the unstable heat release may shift to match one of the combustors natural acoustic frequencies which then can result in significant energy exchange from chemical to acoustic energy resulting in thermoacoustic instability. The mechanisms of the fluid mechanics in coupling combustion to acoustics are very broad with many varying mechanisms explained in detail in the first chapter. Significant effort is made in understanding these mechanisms in this research in order to find commonalities, useful for mitigating multiple instability mechanisms. The complexity of combustion instabilities makes mitigation of combustion instabilities very difficult as few mitigation methods have historically proven to be very effective for broad ranges of combustion instabilities. This research identifies turbulence intensity near the forward stagnation point and movement of the forward stagnation point as a common link in what would otherwise appear to be very different instabilities. The most common method of stabilization of both premixed and diffusion flame combustion is through the introduction of swirl. Reverse flow along the centerline is introduced to transport heat and chemically active combustion products back upstream to sustain combustion. This research develops methods to suppress the movement of the forward stagnation point without suppressing the development of the vortex breakdown process which is critical to the transport of heat and reactive species necessary for flame stabilization. These methods are useful in suppressing the local turbulence at the forward stagnation point, limiting dissipation of heat and reactive species significantly improving stability. Combustion hardware is developed and tested to demonstrate the stability principles developed as part of this research. In order to more completely understand combustion instability a very unique method of combustion was researched where there are no discrete points of combustion initiation such as the forward stagnation point typical in many combustion systems including swirl and jet wake stabilized combustion. This class of combustion which has empirical evidence of great stability and efficient combustion with low CO, NOx and UHC emissions is described as high oxidization temperature distributed combustion. This mechanism of combustion is shown to be stable largely because there are no stagnations points susceptible to fluid mechanic perturbations. The final topic of research is active combustion control by fuel modulation. This may be the only practical method of controlling most instabilities with a single technique. As there are many papers reporting active combustion control algorithms this research focused on the complexities of the physics of fuel modulation at frequencies up to 1000 Hz with proportionally controlled flow amplitude. This research into the physics of high speed fluid movement, oscillation mechanical mechanisms and electromagnetics are demonstrated by development and testing of a High Speed Latching Oscillator Valve.
Author: Rudibert King
Publisher: Springer
ISBN: 3319981773
Category : Technology & Engineering
Languages : en
Pages : 380
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Book Description
The book reports on the latest theoretical and experimental findings in the field of active flow and combustion control. It covers new developments in actuator technology and sensing, in robust and optimal open- and closed-loop control, as well as in model reduction for control, constant volume combustion and dynamic impingement cooling. The chapters reports oncutting-edge contributions presented during the fourth edition of the Active Flow and Combustion Control conference, held in September 19 to 21, 2018 at the Technische Universität Berlin, in Germany. This conference, as well as the research presented in the book, have been supported by the collaborative research center SFB 1029 on “Substantial efficiency increase in gas turbines through direct use of coupled unsteady combustion and flow dynamics”, funded by the DFG (German Research Foundation). It offers a timely guide for researchers and practitioners in the field of aeronautics, turbomachinery, control and combustion.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721677191
Category :
Languages : en
Pages : 30
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Book Description
This paper describes ongoing testing of an adaptive control method to suppress high frequency thermo-acoustic instabilities like those found in lean-burning, low emission combustors that are being developed for future aircraft gas turbine engines. The method called Adaptive Sliding Phasor Averaged Control, was previously tested in an experimental rig designed to simulate a combustor with an instability of about 530 Hz. Results published earlier, and briefly presented here, demonstrated that this method was effective in suppressing the instability. Because this test rig did not exhibit a well pronounced instability, a question remained regarding the effectiveness of the control methodology when applied to a more coherent instability. To answer this question, a modified combustor rig was assembled at the NASA Glenn Research Center in Cleveland, Ohio. The modified rig exhibited a more coherent, higher amplitude instability, but at a lower frequency of about 315 Hz. Test results show that this control method successfully reduced the instability pressure of the lower frequency test rig. In addition, due to a certain phenomena discovered and reported earlier, the so called Intra-Harmonic Coupling, a dramatic suppression of the instability was achieved by focusing control on the second harmonic of the instability. These results and their implications are discussed, as well as a hypothesis describing the mechanism of intra-harmonic coupling. Kopasakis, George and DeLaat, John C. and Chang, Clarence T. Glenn Research Center NASA/TM-2004-213198, AIAA Paper 2004-4028, E-14698
