The Experts below are selected from a list of 17040 Experts worldwide ranked by ideXlab platform
Serafettin Engin - One of the best experts on this subject based on the ideXlab platform.
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time optimized hole sequence planning for 5 axis on the fly laser drilling
Cirp Annals-manufacturing Technology, 2014Co-Authors: Kaan Erkorkmaz, Ammar Alzaydi, Amr Elfizy, Serafettin EnginAbstract:Abstract On-the-fly laser drilling requires the use of acceleration continuous trajectories, which are typically planned using time parameterized spline functions. In this operation, the choice of hole drilling sequence, and positioning timings in between the holes, play a critical role in determining the achievable cycle time. This paper presents a new algorithm for sequencing 5-axis on-the-fly laser drilling hole locations and timings. The algorithm considers machine tool and process constraints, as well as the temporal nature of the final commanded spline trajectory. The achievable productivity and motion smoothness improvement are demonstrated in the production of a Gas Turbine Combustion chamber panel.
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time optimal trajectory generation for 5 axis on the fly laser drilling
Cirp Annals-manufacturing Technology, 2011Co-Authors: Kaan Erkorkmaz, Ammar Alzaydi, Amr Elfizy, Serafettin EnginAbstract:Abstract This paper presents a new and time-optimal trajectory generation technique for 5-axis on-the-fly laser drilling. Trajectories for individual hole clusters are optimized by minimizing the integral square of the 4th time derivative, and by adjusting the velocity and acceleration conditions at the hole locations to enable the maximum time compression (i.e., highest laser pulsing frequency). Axis velocity, acceleration, jerk, and hole elongation constraints are also considered. Individually optimized clusters are stitched together using time-optimal segments with nonzero velocity boundary conditions. The practicality and effectiveness of the algorithm is demonstrated in implementation results for producing a Gas Turbine Combustion chamber component.
Thierry Poinsot - One of the best experts on this subject based on the ideXlab platform.
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comparison of nonlinear to linear thermoacoustic stability analysis of a Gas Turbine Combustion system
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, 2012Co-Authors: Werner Krebs, Thierry Poinsot, Harmen Krediet, Enrique Portillo, Sebastian Hermeth, Sebastian Schimek, Oliver PaschereitAbstract:Gas Turbines offer a high operational flexibility and a good turn down ratio to meet future requirements of power production. In this context stable operation over a wide range and for different blends of fuel is requested. Thermoacoustic stability assessment is crucial for accelerating the development and implementation of new Combustion systems.The results of nonlinear and linear thermoacoustic stability assessments are compared on basis of recent measurements of flame describing functions and thermoacoustic stability of a model swirl combustor operating in the fully turbulent regime. The different assessment methods are outlined. The linear thermoacoustic stability assessment yields growth rates of the thermoacoustic instability whereas the limit cycle amplitude is predicted by the nonlinear stability method.It could be shown that the predicted limit cycle amplitudes correlate well with the growth rates of excitation obtained from linear modeling. Hence for screening the thermoacoustic stability of different design approaches a linear assessment may be sufficient while for detailed prediction of the dynamic pressure amplitude more efforts have to be spent on the nonlinear assessment including the analysis of the nonlinear flame response.Copyright © 2012 by ASME
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Large Eddy Simulations of Gaseous flames in Gas Turbine Combustion chambers
Progress in Energy and Combustion Science, 2012Co-Authors: Laurent Y.m. Gicquel, Gabriel Staffelbach, Thierry PoinsotAbstract:Recent developments in numerical schemes, turbulent Combustion models and the regular increase of computing power allow Large Eddy Simulation (LES) to be applied to real industrial burners. In this paper, two types of LES in complex geometry combustors and of specific interest for aeronautical Gas Turbine burners are reviewed: (1) laboratory-scale combustors, without compressor or Turbine, in which advanced measurements are possible and (2) Combustion chambers of existing engines operated in realistic operating conditions. Laboratory-scale burners are designed to assess modeling and funda- mental flow aspects in controlled configurations. They are necessary to gauge LES strategies and identify potential limitations. In specific circumstances, they even offer near model-free or DNS-like LES computations. LES in real engines illustrate the potential of the approach in the context of industrial burners but are more difficult to validate due to the limited set of available measurements. Usual approaches for turbulence and Combustion sub-grid models including chemistry modeling are first recalled. Limiting cases and range of validity of the models are specifically recalled before a discussion on the numerical breakthrough which have allowed LES to be applied to these complex cases. Specific issues linked to real Gas Turbine chambers are discussed: multi-perforation, complex acoustic impedances at inlet and outlet, annular chambers.. Examples are provided for mean flow predictions (velocity, temperature and species) as well as unsteady mechanisms (quenching, ignition, Combustion instabil- ities). Finally, potential perspectives are proposed to further improve the use of LES for real Gas Turbine combustor designs.
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Outlet-Boundary-Condition Influence for Large Eddy Simulation of Combustion Instabilities in Gas Turbines
Journal of Propulsion and Power, 2008Co-Authors: Sébastien Roux, Michel Cazalens, Thierry PoinsotAbstract:Large eddy simulations of Combustion require more precise boundary conditions than classical Reynolds-averaged methods. This study shows how the reacting flow within a Gas Turbine Combustion chamber can be influenced by the description of the downstream boundary. Large eddy simulation calculations are performed on a Combustion chamber terminated by a high-pressure stator containing vanes in which the flow is usually choked and submitted to strong rotation effects. High-pressure stators are present in all real Gas Turbines, but they are often not computed and are simply replaced by a constant-pressure-outlet condition. This study compares a large eddy simulation calculation in which the high-pressure stator is replaced by a constant-pressure-outlet surface and a large eddy simulation in which the high-pressure stator is included in the computational domain and explicitly computed. The comparison of the flow in the chamber in both large eddy simulations reveals that the presence of the high-pressure stator modifies the mean flow in the second part of the chamber but does not affect the primary Combustion zone. The unsteady field, on the other hand, is strongly affected by the high-pressure stator. Results demonstrate that the high-pressure stator should be included in realistic large eddy simulations of Combustion chambers for Gas Turbines.
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comparison of les rans and experiments in an aeronautical Gas Turbine Combustion chamber
Proceedings of the Combustion Institute, 2007Co-Authors: G Boudier, Laurent Gicquel, Thierry Poinsot, D Bissieres, Claude BeratAbstract:Abstract Although Large Eddy Simulations (LES) have demonstrated their potential in simple academic Combustion chambers, their application to real Gas Turbine chambers requires specific developments and validations. In this study, three specific aspects of such chambers are discussed: multiple inlets, multi-perforated plates and film cooling. LES are used in an industry-like chamber and results are compared with predictions provided by Reynolds Averaged Navier–Stokes (RANS) simulations and experimental measurements. Multi-perforation is handled using a simplified effusive wall law while film cooling makes use of low resolution influx conditions (‘coarse LES’). Experimental results are well reproduced and qualitatively improved when compared to RANS predictions. LES results underline the potential of the approach for industrial use.
Ahmed F Ghoniem - One of the best experts on this subject based on the ideXlab platform.
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turbulent flame stabilization modes in premixed swirl Combustion physical mechanism and karlovitz number based criterion
Combustion and Flame, 2016Co-Authors: Soufien Taamallah, Santosh J Shanbhogue, Ahmed F GhoniemAbstract:Abstract Modern low-emission, lean premixed Gas Turbine Combustion systems often rely on confined swirling flows associated with sudden expansions to enhance flame anchoring. Through the establishment of multiple recirculation zones and shear layers, such complex reacting flows give rise to several possible average flame shapes or macrostructures. Among these, the single conical flame stabilized along the inner shear layer (ISL) and the double conical flame stabilized along both the inner as well as the outer shear layers (OSL) and the outer recirculation zone (ORZ) are of special interest. One of the reasons is that the transition between these two flames has been previously linked to the onset of thermo-acoustic instabilities under acoustically coupled conditions. In this study we investigate the mechanism underlying the flame transition to the ORZ/OSL and propose a criterion for its occurrence, in an acoustically uncoupled Combustion system. To reach this goal, the effects of the fuel composition (CH 4 –H 2 ), Reynolds number, swirler blade angle and heat loss were experimentally analyzed. We find evidence that the transition starts with an intermittent inflammation of the ORZ caused by a flame kernel detaching from the ISL. Above a critical equivalence ratio, the flame kernel expands and spins along with the ORZ flow. Next, we explore the effect of the operating conditions on the onset of an ORZ flame. We propose a Strouhal number to describe the ORZ flame spinning frequency ( f ORZ ) also shown to be a predominately hydrodynamic quantity. Finally, we show that the flame transition to the ORZ is governed by a balance between a flame time to a flow time that can be expressed in a form of a Karlovitz number ( Ka ORZ ) defined as the ratio of the ORZ spinning frequency and extinction strain rate; the former is a surrogate for the bulk azimuthal strain rate in the ORZ.
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Fuel flexibility, stability and emissions in premixed hydrogen-rich Gas Turbine Combustion: Technology, fundamentals, and numerical simulations
Applied Energy, 2015Co-Authors: S. Taamallah, Fatimah Mohammed Alzahrani, Konstantina Vogiatzaki, Esmail Mohamed Ali Mokheimer, M. A. Habib, Ahmed F GhoniemAbstract:The objective of this paper is to review the progress made in understanding the effects of fuel composition on premixed Gas Turbine Combustion, with a special emphasis on system stability and emissions, for hydrogen-rich synthetic Gas (synGas) mixtures. This is driven by the rising interest in the use of hydrogen blends and synGas in combined cycle power plants, as an alternative to standard natural Gas. Typical applications where such mixtures are used include the recycling of hydrogen by-product from industry as well as promising pre-Combustion carbon capture methods like fuel reforming or Gasification integrated with Gas Turbine combined cycle plants. SynGas is mainly a mixture of H2, CO and CH4; its composition can vary due to fluctuations in the process's conditions but can also dramatically change if the feedstock is modified like coal or biomass grades in Gasification. Due to the substantially different chemical, transport and thermal properties that distinguish the synGas components, especially H2, when compared with conventional hydrocarbon fuels, these non-standard fuels pose several challenges in premixed Combustion. These challenges are reviewed in this paper along with the Combustion fundamentals of these fuels. A survey of available technologies able to handle synGas and hydrogen-rich fuel in general is provided reflecting the difficulties encountered while using these fuels in real large scale commercial applications. We find that a limited number of options exist today for fully premixed Combustion, but promising designs are under development. Finally, the ever growing use of numerical simulation to cost-effectively study full scale Combustion systems-with Large Eddy Simulations (LES) being at the forefront as a compromise between accuracy and computational cost-justifies the simultaneous review of the different numerical attempts to simulate hydrogen-containing fuel mixtures and synGas in premixed Combustion. Challenges specific to performing LES calculations for these reacting flows are highlighted. We find that, while the literature on premixed LES methane Combustion is abundant, LES of premixed synGas and hydrogen-rich fuels Combustion is comparatively scarce. Only few attempts were made so far showing the need for more research effort in this area to help tackle the challenges presented by these fuels.
Kaan Erkorkmaz - One of the best experts on this subject based on the ideXlab platform.
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time optimized hole sequence planning for 5 axis on the fly laser drilling
Cirp Annals-manufacturing Technology, 2014Co-Authors: Kaan Erkorkmaz, Ammar Alzaydi, Amr Elfizy, Serafettin EnginAbstract:Abstract On-the-fly laser drilling requires the use of acceleration continuous trajectories, which are typically planned using time parameterized spline functions. In this operation, the choice of hole drilling sequence, and positioning timings in between the holes, play a critical role in determining the achievable cycle time. This paper presents a new algorithm for sequencing 5-axis on-the-fly laser drilling hole locations and timings. The algorithm considers machine tool and process constraints, as well as the temporal nature of the final commanded spline trajectory. The achievable productivity and motion smoothness improvement are demonstrated in the production of a Gas Turbine Combustion chamber panel.
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time optimal trajectory generation for 5 axis on the fly laser drilling
Cirp Annals-manufacturing Technology, 2011Co-Authors: Kaan Erkorkmaz, Ammar Alzaydi, Amr Elfizy, Serafettin EnginAbstract:Abstract This paper presents a new and time-optimal trajectory generation technique for 5-axis on-the-fly laser drilling. Trajectories for individual hole clusters are optimized by minimizing the integral square of the 4th time derivative, and by adjusting the velocity and acceleration conditions at the hole locations to enable the maximum time compression (i.e., highest laser pulsing frequency). Axis velocity, acceleration, jerk, and hole elongation constraints are also considered. Individually optimized clusters are stitched together using time-optimal segments with nonzero velocity boundary conditions. The practicality and effectiveness of the algorithm is demonstrated in implementation results for producing a Gas Turbine Combustion chamber component.
Bruno Schuermans - One of the best experts on this subject based on the ideXlab platform.
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analysis of azimuthal thermo acoustic modes in annular Gas Turbine Combustion chambers
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2014Co-Authors: Mirko Ruben Bothien, Nicolas Noiray, Bruno SchuermansAbstract:Modern Gas Turbine combustors operating in lean-premixed mode are prone to thermoacoustic instabilities. In annular Combustion chambers, usually azimuthal acoustic modes are the critical ones interacting with the flame. In case of constructive interference, high amplitude oscillations might result. In this paper, the azimuthal acoustic field of a full-scale engine is investigated in detail. The analyses are based on measurements in a full-scale Gas Turbine, analytical models to derive the system dynamics, as well as simulations performed with an in-house 3d nonlinear network model. It is shown that the network model is able to reproduce the behaviour observed in the engine. Spectra, linear growth rates, as well as the statistics of the system’s dynamics can be predicted. A previously introduced algorithm is used to extract linear growth rates from engine and model time domain data. The method’s accuracy is confirmed by comparison of the routine’s results to analytically determined growth rates from the network model. The network model is also used to derive a burner staging configuration resulting in the decrease of linear growth rate and thus an increase of engine operation regime; model predictions are verified by full-scale engine measurements. A thorough investigation of the azimuthal modes statistics is performed. Additionally, the network model is used to show that an unfavorable flame temperature distribution with an amplitude of merely 1% of the mean flame temperature can change the azimuthal mode from dominantly rotating to dominantly standing. This is predicted by the network model that only takes into account flame fluctuations in axial direction.© 2014 ASME
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on the dynamic nature of azimuthal thermoacoustic modes in annular Gas Turbine Combustion chambers
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2013Co-Authors: Nicolas Noiray, Bruno SchuermansAbstract:This paper deals with the dynamics of standing and rotating azimuthal thermoacoustic modes in annular Combustion chambers. Simultaneous acoustic measurements have been made at multiple circumferential positions in an annular Gas Turbine Combustion chamber. A detailed statistical analysis of the spatial Fourier amplitudes extracted from these data reveals that the acoustic modes are continuously switching between standing, clockwise and counter-clockwise travelling waves. A theoretical framework from which the modal dynamics can be explained is proposed and supported by real Gas Turbine data. The stochastic differential equations that govern these systems have been derived and used as a basis for system identification of the measured engine data. The model describes the probabilities of the two azimuthal wave components as a function of the random source intensity, the asymmetry in the system and the strength of the thermoacoustic interaction. The solution of the simplified system is in good agreement with experimental observations on a Gas Turbine Combustion chamber.
