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Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. - Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work - Addresses the challenges of turbulent combustion modeling with numerical simulations - Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities - Covers the design of a fully premixed injector for future jet engine applications
Combustion in a lean pre-mixed (LPM) combustor may become unstable due to small changes in geometry and the manner in which reactants are introduced. This may lead to excessive thermal loads and possible off-design operation. A comprehensive understanding of combustion instability is therefore needed. The present study aims to analyze the flow and flame dynamics in a model LPM gas turbine combustor in LPM combustion. Fluent is used as the flow solver for the present study. The 3-D Navier-Stokes equations are solved along with finite-rate chemical reaction equations and variable thermo-physical properties. Large-eddy-simulation (LES) technique is used to model turbulence. The dynamic version of the Smagorinsky-Lilly model is employed to describe subgrid-scale turbulent motions and their effect on large-scale structures. At first a non-reactive LES was performed in model round and LM6000 combustor. The results for time averaged mean velocity are compared with the previous LES work by Grinstein et al. and Kim et al. Using non-reacting case for LM6000, reactive simulation was initiated, with lean methane-air mixture with equivalence ratio 0.56. Species transport equation is solved for global methane-air two-step reaction with six volumetric species to predict the local mass fraction of each species. The reaction rates that appear as source terms in the species transport equation are computed using finite-rate/eddy-dissipation model, which computes both, the Arrhenius rate and the mixing rate and uses the smaller of the two. It is observed that as the flow enters the chamber, it bifurcates in two shear layers forming a prong like structure. The layers further tend to reattach to the wall at a distance approximately equal to 3D. Counter-clockwise recirculation zones are formed in the corners, whereas clock-wise toroidal vortex structure is formed in the center. The flame is located in between these vortex structures and thus experiences shear-layer instabilities. It is also noticed that the eddy structure in case of reacting case is thicker than that of the non-reacting case. This is mainly due to the temperature dependent viscosity, which has a stabilizing effect on the flow.
Blending fuels with hydrogen offers the potential to reduce NOx and CO2 emissions in gas turbines, but doing so introduces potential new problems such as flashback. Flashback can lead to thermal overload and destruction of hardware in the turbine engine, with potentially expensive consequences. The little research on flashback that is available is fragmented. Flashback Mechanisms in Lean Premixed Gas Turbine Combustion by Ali Cemal Benim will address not only the overall issue of the flashback phenomenon, but also the issue of fragmented and incomplete research. - Presents a coherent review of flame flashback (a classic problem in premixed combustion) and its connection with the growing trend of popularity of more-efficient hydrogen-blend fuels - Begins with a brief review of industrial gas turbine combustion technology - Covers current environmental and economic motivations for replacing natural gas with hydrogen-blend fuels
Reviews our current understanding of the subject. For graduate students and researchers in computational fluid dynamics and turbulence.
This book offers gas turbine users and manufacturers a valuable resource to help them sort through issues associated with combustion instabilities. In the last ten years, substantial efforts have been made in the industrial, governmental, and academic communities to understand the unique issues associated with combustion instabilities in low-emission gas turbines. The objective of this book is to compile these results into a series of chapters that address the various facets of the problem. The Case Studies section speaks to specific manufacturer and user experiences with combustion instabilities in the development stage and in fielded turbine engines. The book then goes on to examine The Fundamental Mechanisms, The Combustor Modeling, and Control Approaches.
Describes combustion dynamics in gas turbine combustors. Analyses combustion response of a single premixed injector to longitudinal pressure disturbances and three-dimensional flow simulations of a multi-element injector combustor under steady-state conditions.
Increasingly stringent regulations as well as environmental concerns have lead gas turbine powered engine manufacturers to develop the current generation of combustors, which feature lower than ever fuel consumption and pollutant emissions. However, modern combustor designs have been shown to be prone to combustion instabilities, where the coupling between acoustics of the combustor and the flame results in large pressure oscillations and vibrations within the combustion chamber. These instabilities can cause structural damages to the engine or even lead to its destruction. At the same time, considerable developments have been achieved in the numerical simulation domain, and Computational Fluid Dynamics (CFD) has proven capable of capturing unsteady flame dynamics and combustion instabilities for aforementioned engines. Still, even with the current large and fast increasing computing capabilities, time remains the key constraint for these high fidelity yet computationally intensive calculations. Typically, covering the entire range of operating conditions for an industrial engine is still out of reach. In that respect, low order models exist and can be efficient at predicting the occurrence of combustion instabilities, provided an adequate modeling of the flame/acoustics interaction as appearing in the system is available. This essential piece of information is usually recast as the so called Flame Transfer Function (FTF) relating heat release rate fluctuations to velocity fluctuations at a given point. One way to obtain this transfer function is to rely on analytical models, but few exist for turbulent swirling flames. Another way consists in performing costly experiments or numerical simulations, negating the requested fast prediction capabilities. This thesis therefore aims at providing fast, yet reliable methods to allow for low order combustion instabilities modeling. In that context, understanding the underlying mechanisms of swirling flame acoustic response is also targeted. To address this issue, a novel hybrid approach is first proposed based on a reduced set of high fidelity simulations that can be used to determine input parameters of an analytical model used to express the FTF of premixed swirling flames. The analytical model builds on previous works starting with a level-set description of the flame front dynamics while also accounting for the acoustic-vorticity conversion through a swirler. For such a model, validation is obtained using reacting stationary and pulsed numerical simulations of a laboratory scale premixed swirl stabilized flame. The model is also shown to be able to handle various perturbation amplitudes. At last, 3D high fidelity simulations of an industrial gas turbine powered by a swirled spray flame are performed to determine whether a combustion instability observed in experiments can be predicted using numerical analysis. To do so, a series of forced simulations is carried out in en effort to highlight the importance of the two-phase flow flame response evaluation. In that case, sensitivity to reference velocity perturbation probing positions as well as the amplitude and location of the acoustic perturbation source are investigated. The analytical FTF model derived in the context of a laboratory premixed swirled burner is furthermore gauged in this complex case. Results show that the unstable mode is predicted by the acoustic analysis, but that the flame model proposed needs further improvements to extend its applicability range and thus provide data relevant to actual aero-engines.
This book presents a comprehensive review of state-of-the-art models for turbulent combustion, with special emphasis on the theory, development and applications of combustion models in practical combustion systems. It simplifies the complex multi-scale and nonlinear interaction between chemistry and turbulence to allow a broader audience to understand the modeling and numerical simulations of turbulent combustion, which remains at the forefront of research due to its industrial relevance. Further, the book provides a holistic view by covering a diverse range of basic and advanced topics—from the fundamentals of turbulence–chemistry interactions, role of high-performance computing in combustion simulations, and optimization and reduction techniques for chemical kinetics, to state-of-the-art modeling strategies for turbulent premixed and nonpremixed combustion and their applications in engineering contexts.