The Experts below are selected from a list of 184437 Experts worldwide ranked by ideXlab platform
Sébastien Candel - One of the best experts on this subject based on the ideXlab platform.
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nonlinear combustion Instability Analysis based on the flame describing function applied to turbulent premixed swirling flames
Combustion and Flame, 2011Co-Authors: Paul Palies, Sébastien Candel, Thierry Schuller, Daniel DuroxAbstract:Abstract Instability Analysis of swirling flames is of importance in the design of advanced combustor concepts for aircraft propulsion and powerplant for electricity production. Thermoacoustic instabilities are analyzed here by making use of a nonlinear representation of flame dynamics based on a describing function. In this framework, the flame response is determined as a function of frequency and amplitude of perturbations impinging on the combustion region. This model is adapted to the case of confined swirling flames comprising an upstream manifold, an injection unit equipped with a swirler and a cylindrical flame tube. The flame describing function is experimentally determined and is combined with an acoustic transfer matrix representation of the system to provide growth rates and oscillation frequencies as a function of perturbation amplitude. These data can be used to determine regions of Instability, frequency shifts with respect to the acoustic eigenfrequencies and they also yield amplitude levels when self-sustained oscillations of the system have reached a limit cycle. This equilibrium is obtained when the amplitude dependent growth rate equals the damping rate in the system. This requires an independent determination of this last quantity which is here based on measurements of the combustor resonance response curve, together with numerical estimates of the flame contribution to the system response. The geometrical parameters of the upstream manifold and flame tube are varied and the corresponding operating regimes are compared with those predicted with the FDF framework. The present demonstration of the FDF framework in a generic configuration indicates that this can be used in more general situations of technological interest.
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a unified framework for nonlinear combustion Instability Analysis based on the flame describing function
Journal of Fluid Mechanics, 2008Co-Authors: Nicolas Noiray, Daniel Durox, Thierry Schuller, Sébastien CandelAbstract:Analysis of combustion instabilities relies in most cases on linear Analysis but most observations of these processes are carried out in the nonlinear regime where the system oscillates at a limit cycle. The objective of this paper is to deal with these two manifestations of combustion instabilities in a unified framework. The flame is recognized as the main nonlinear element in the system and its response to perturbations is characterized in terms of generalized transfer functions which assume that the gain and phase depend on the amplitude level of the input. This 'describing function' framework implies that the fundamental frequency is predominant and that the higher harmonics generated in the nonlinear element are weak because the higher frequencies are filtered out by the other components of the system. Based on this idea, a methodology is proposed to investigate the nonlinear stability of burners by associating the flame describing function with a frequency-domain Analysis of the burner acoustics. These elements yield a nonlinear dispersion relation which can be solved, yielding growth rates and eigenfrequencies, which depend on the amplitude level of perturbations impinging on the flame. This method is used to investigate the regimes of oscillation of a well-controlled experiment. The system includes a resonant upstream manifold formed by a duct having a continuously adjustable length and a combustion region comprising a large number of flames stabilized on a multipoint injection system. The growth rates and eigenfrequencies are determined for a wide range of duct lengths. For certain values of this parameter we find a positive growth rate for vanishingly small amplitude levels, indicating that the system is linearly unstable. The growth rate then changes as the amplitude is increased and eventually vanishes for a finite amplitude, indicating the existence of a limit cycle. For other values of the length, the growth rate is initially negative, becomes positive for a finite amplitude and drops to zero for a higher value. This indicates that the system is linearly stable but nonlinearly unstable. Using calculated growth rates it is possible to predict amplitudes of oscillation when the system operates on a limit cycle. Mode switching and Instability triggering may also be anticipated by comparing the growth rate curves. Theoretical results are found to be in excellent agreement with measurements, indicating that the flame describing function (FDF) methodology constitutes a suitable framework for nonlinear Instability Analysis.
Frede Blaabjerg - One of the best experts on this subject based on the ideXlab platform.
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harmonic Instability assessment using state space modeling and participation Analysis in inverter fed power systems
IEEE Transactions on Industrial Electronics, 2017Co-Authors: Yanbo Wang, Frede Blaabjerg, Xiongfei Wang, Zhe ChenAbstract:This paper presents a harmonic Instability Analysis method using state-space modeling and participation Analysis in the inverter-fed ac power systems. A full-order state-space model for the droop-controlled distributed generation (DG) inverter is built first, including the time delay of the digital control system, inner current and voltage control loops, and outer droop-based power control loop. Based on the DG inverter model, an overall state-space model of a two-inverter-fed system is established. The eigenvalue-based stability Analysis is then presented to assess the influence of controller parameters on the harmonic Instability of the power system. Moreover, the harmonic-frequency oscillation modes are identified, where participation Analysis is presented to evaluate the contributions of different states to these modes and to further reveal how the system gives rise to harmonic Instability. Based on the participation Analysis, a reduced-order model for harmonic Instability Analysis is also proposed. The experimental results are presented for validating the theoretical analyses.
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Harmonic Instability Analysis of a Single-Phase Grid-Connected Converter Using a Harmonic State-Space Modeling Method
IEEE Transactions on Industry Applications, 2016Co-Authors: Jun Bum Kwon, Frede Blaabjerg, Xiongfei Wang, Claus Leth Bak, Alan R. Wood, Neville R. WatsonAbstract:The increasing number of renewable energy sources in the distribution grid is becoming a major issue for utility companies since grid-connected converters are operating at different operating points due to the probabilistic characteristics of the renewable energy. Usually, the harmonics and impedance from other renewable energy sources are not taken carefully into account in the installation and design of the systems. It can bring an unknown harmonic Instability into a multiple power-sourced system and makes the Analysis difficult due to the complexity of the grid network. This paper proposes a new model of a single-phase grid-connected renewable energy source by using the harmonic state-space modeling approach, which can identify such problems. The model can be extended to a multiple connected converter Analysis. The modeling results show the harmonic impedance matrixes, which represent the harmonic coupling characteristic, as well as different dynamic characteristics. The theoretical modeling and Analysis are verified by simulations, as well as experimental results.
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Harmonic Instability Analysis of single-phase grid connected converter using Harmonic State Space (HSS) modeling method
2015 IEEE Energy Conversion Congress and Exposition (ECCE), 2015Co-Authors: Jun Bum Kwon, Xiongfei Wang, Claus Leth Bak, Frede BlaabjergAbstract:The increasing number of renewable energy sources at the distribution grid is becoming a major issue for utility companies, since the grid connected converters are operating at different operating points due to the probabilistic characteristics of renewable energy. Besides, typically, the harmonics and impedance from other renewable energy sources are not taken carefully into account in the installation and design. However, this may bring an unknown harmonic Instability into the multiple power sourced system and also make the Analysis difficult due to the complexity of the grid network. This paper proposes a new model of a single phase grid connected renewable energy source using the Harmonic State Space modeling approach, which is able to identify such problems and the model can be extended to be applied in the multiple connected converter Analysis. The modeling results show the different harmonic impedance matrixes, where that represents the harmonic coupling characteristic as well as the different Instability characteristics. The theoretical modeling and Analysis are verified by simulations and also experimental results.
Hele L Reed - One of the best experts on this subject based on the ideXlab platform.
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secondary Instability Analysis of crossflow on a hypersonic yawed straight circular cone
Journal of Fluid Mechanics, 2017Co-Authors: Alexande Moyes, Pedro Paredes, Travis S Kocia, Hele L ReedAbstract:The purpose of this paper is to provide secondary Instability Analysis of stationary crossflow vortices on a hypersonic yawed straight circular cone with a $7^{\circ }$ half-angle at $6^{\circ }$ angle of attack, free-stream Mach number 6 and unit Reynolds number $10.09\times 10^{6}~\text{m}^{-1}$ . At an angle of attack, a three-dimensional boundary layer is developed between the windward and leeward symmetry planes. Under the action of azimuthal pressure gradients, the flow near the surface is deflected more than the flow near the edge of the boundary layer. This results in an inflectional velocity profile that can sustain the growth of crossflow vortices. The stationary crossflow Instability is computed by means of the nonlinear parabolized stability equations, including a methodology to predict the stationary-crossflow marching path and variation of the spanwise number of waves in the marching direction solely from the basic state. Secondary Instability Analysis is performed using spatial BiGlobal equations based on two-dimensional partial differential equations. The secondary instabilities are calculated at different axial locations along two crossflow vortex trajectories selected to complement experiments conducted in the Mach 6 Quiet Tunnel at Texas A&M University and in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University. The secondary Instability Analysis captures various Instability modes. Similar to observations in the low-speed regime for an infinite swept wing, secondary shear-layer instabilities are amplified as a consequence of the three-dimensional shear layer formed by crossflow vortices. Also, low-frequency travelling crossflow and high-frequency second modes coexist with the shear-layer instabilities. These results are shown to be in good agreement with the two sets of hypersonic yawed cone experiments (one with natural surface roughness and one with artificial discrete roughness) and compare well with experimental measurements of an incompressible swept wing.
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secondary Instability Analysis of crossflow on a hypersonic yawed straight circular cone
Journal of Fluid Mechanics, 2017Co-Authors: Alexander Moyes, Pedro Paredes, Travis S Kocian, Hele L ReedAbstract:The purpose of this paper is to provide secondary Instability Analysis of stationary crossflow vortices on a hypersonic yawed straight circular cone with a half-angle at angle of attack, free-stream Mach number 6 and unit Reynolds number . At an angle of attack, a three-dimensional boundary layer is developed between the windward and leeward symmetry planes. Under the action of azimuthal pressure gradients, the flow near the surface is deflected more than the flow near the edge of the boundary layer. This results in an inflectional velocity profile that can sustain the growth of crossflow vortices. The stationary crossflow Instability is computed by means of the nonlinear parabolized stability equations, including a methodology to predict the stationary-crossflow marching path and variation of the spanwise number of waves in the marching direction solely from the basic state. Secondary Instability Analysis is performed using spatial BiGlobal equations based on two-dimensional partial differential equations. The secondary instabilities are calculated at different axial locations along two crossflow vortex trajectories selected to complement experiments conducted in the Mach 6 Quiet Tunnel at Texas A&M University and in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University. The secondary Instability Analysis captures various Instability modes. Similar to observations in the low-speed regime for an infinite swept wing, secondary shear-layer instabilities are amplified as a consequence of the three-dimensional shear layer formed by crossflow vortices. Also, low-frequency travelling crossflow and high-frequency second modes coexist with the shear-layer instabilities. These results are shown to be in good agreement with the two sets of hypersonic yawed cone experiments (one with natural surface roughness and one with artificial discrete roughness) and compare well with experimental measurements of an incompressible swept wing.
Pedro Paredes - One of the best experts on this subject based on the ideXlab platform.
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secondary Instability Analysis of crossflow on a hypersonic yawed straight circular cone
Journal of Fluid Mechanics, 2017Co-Authors: Alexande Moyes, Pedro Paredes, Travis S Kocia, Hele L ReedAbstract:The purpose of this paper is to provide secondary Instability Analysis of stationary crossflow vortices on a hypersonic yawed straight circular cone with a $7^{\circ }$ half-angle at $6^{\circ }$ angle of attack, free-stream Mach number 6 and unit Reynolds number $10.09\times 10^{6}~\text{m}^{-1}$ . At an angle of attack, a three-dimensional boundary layer is developed between the windward and leeward symmetry planes. Under the action of azimuthal pressure gradients, the flow near the surface is deflected more than the flow near the edge of the boundary layer. This results in an inflectional velocity profile that can sustain the growth of crossflow vortices. The stationary crossflow Instability is computed by means of the nonlinear parabolized stability equations, including a methodology to predict the stationary-crossflow marching path and variation of the spanwise number of waves in the marching direction solely from the basic state. Secondary Instability Analysis is performed using spatial BiGlobal equations based on two-dimensional partial differential equations. The secondary instabilities are calculated at different axial locations along two crossflow vortex trajectories selected to complement experiments conducted in the Mach 6 Quiet Tunnel at Texas A&M University and in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University. The secondary Instability Analysis captures various Instability modes. Similar to observations in the low-speed regime for an infinite swept wing, secondary shear-layer instabilities are amplified as a consequence of the three-dimensional shear layer formed by crossflow vortices. Also, low-frequency travelling crossflow and high-frequency second modes coexist with the shear-layer instabilities. These results are shown to be in good agreement with the two sets of hypersonic yawed cone experiments (one with natural surface roughness and one with artificial discrete roughness) and compare well with experimental measurements of an incompressible swept wing.
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secondary Instability Analysis of crossflow on a hypersonic yawed straight circular cone
Journal of Fluid Mechanics, 2017Co-Authors: Alexander Moyes, Pedro Paredes, Travis S Kocian, Hele L ReedAbstract:The purpose of this paper is to provide secondary Instability Analysis of stationary crossflow vortices on a hypersonic yawed straight circular cone with a half-angle at angle of attack, free-stream Mach number 6 and unit Reynolds number . At an angle of attack, a three-dimensional boundary layer is developed between the windward and leeward symmetry planes. Under the action of azimuthal pressure gradients, the flow near the surface is deflected more than the flow near the edge of the boundary layer. This results in an inflectional velocity profile that can sustain the growth of crossflow vortices. The stationary crossflow Instability is computed by means of the nonlinear parabolized stability equations, including a methodology to predict the stationary-crossflow marching path and variation of the spanwise number of waves in the marching direction solely from the basic state. Secondary Instability Analysis is performed using spatial BiGlobal equations based on two-dimensional partial differential equations. The secondary instabilities are calculated at different axial locations along two crossflow vortex trajectories selected to complement experiments conducted in the Mach 6 Quiet Tunnel at Texas A&M University and in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University. The secondary Instability Analysis captures various Instability modes. Similar to observations in the low-speed regime for an infinite swept wing, secondary shear-layer instabilities are amplified as a consequence of the three-dimensional shear layer formed by crossflow vortices. Also, low-frequency travelling crossflow and high-frequency second modes coexist with the shear-layer instabilities. These results are shown to be in good agreement with the two sets of hypersonic yawed cone experiments (one with natural surface roughness and one with artificial discrete roughness) and compare well with experimental measurements of an incompressible swept wing.
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order 104 speedup in global linear Instability Analysis using matrix formation
Computer Methods in Applied Mechanics and Engineering, 2013Co-Authors: Pedro Paredes, Miguel Hermanns, Soledad Le Clainche, Vassilis TheofilisAbstract:Abstract A unified solution framework is presented for one-, two- or three-dimensional complex non-symmetric eigenvalue problems, respectively governing linear modal Instability of incompressible fluid flows in rectangular domains having two, one or no homogeneous spatial directions. The solution algorithm is based on subspace iteration in which the spatial discretization matrix is formed, stored and inverted serially. Results delivered by spectral collocation based on the Chebyshev-Gauss–Lobatto (CGL) points and a suite of high-order finite-difference methods comprising the previously employed for this type of work Dispersion-Relation-Preserving (DRP) and Pade finite-difference schemes, as well as the Summation-by-parts (SBP) and the new high-order finite-difference scheme of order q (FD-q) have been compared from the point of view of accuracy and efficiency in standard validation cases of temporal local and BiGlobal linear Instability. The FD-q method has been found to significantly outperform all other finite difference schemes in solving classic linear local, BiGlobal, and TriGlobal eigenvalue problems, as regards both memory and CPU time requirements. Results shown in the present study disprove the paradigm that spectral methods are superior to finite difference methods in terms of computational cost, at equal accuracy, FD-q spatial discretization delivering a speedup of O ( 10 4 ) . Consequently, accurate solutions of the three-dimensional (TriGlobal) eigenvalue problems may be solved on typical desktop computers with modest computational effort.
Xiongfei Wang - One of the best experts on this subject based on the ideXlab platform.
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harmonic Instability assessment using state space modeling and participation Analysis in inverter fed power systems
IEEE Transactions on Industrial Electronics, 2017Co-Authors: Yanbo Wang, Frede Blaabjerg, Xiongfei Wang, Zhe ChenAbstract:This paper presents a harmonic Instability Analysis method using state-space modeling and participation Analysis in the inverter-fed ac power systems. A full-order state-space model for the droop-controlled distributed generation (DG) inverter is built first, including the time delay of the digital control system, inner current and voltage control loops, and outer droop-based power control loop. Based on the DG inverter model, an overall state-space model of a two-inverter-fed system is established. The eigenvalue-based stability Analysis is then presented to assess the influence of controller parameters on the harmonic Instability of the power system. Moreover, the harmonic-frequency oscillation modes are identified, where participation Analysis is presented to evaluate the contributions of different states to these modes and to further reveal how the system gives rise to harmonic Instability. Based on the participation Analysis, a reduced-order model for harmonic Instability Analysis is also proposed. The experimental results are presented for validating the theoretical analyses.
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Harmonic Instability Analysis of a Single-Phase Grid-Connected Converter Using a Harmonic State-Space Modeling Method
IEEE Transactions on Industry Applications, 2016Co-Authors: Jun Bum Kwon, Frede Blaabjerg, Xiongfei Wang, Claus Leth Bak, Alan R. Wood, Neville R. WatsonAbstract:The increasing number of renewable energy sources in the distribution grid is becoming a major issue for utility companies since grid-connected converters are operating at different operating points due to the probabilistic characteristics of the renewable energy. Usually, the harmonics and impedance from other renewable energy sources are not taken carefully into account in the installation and design of the systems. It can bring an unknown harmonic Instability into a multiple power-sourced system and makes the Analysis difficult due to the complexity of the grid network. This paper proposes a new model of a single-phase grid-connected renewable energy source by using the harmonic state-space modeling approach, which can identify such problems. The model can be extended to a multiple connected converter Analysis. The modeling results show the harmonic impedance matrixes, which represent the harmonic coupling characteristic, as well as different dynamic characteristics. The theoretical modeling and Analysis are verified by simulations, as well as experimental results.
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Harmonic Instability Analysis of single-phase grid connected converter using Harmonic State Space (HSS) modeling method
2015 IEEE Energy Conversion Congress and Exposition (ECCE), 2015Co-Authors: Jun Bum Kwon, Xiongfei Wang, Claus Leth Bak, Frede BlaabjergAbstract:The increasing number of renewable energy sources at the distribution grid is becoming a major issue for utility companies, since the grid connected converters are operating at different operating points due to the probabilistic characteristics of renewable energy. Besides, typically, the harmonics and impedance from other renewable energy sources are not taken carefully into account in the installation and design. However, this may bring an unknown harmonic Instability into the multiple power sourced system and also make the Analysis difficult due to the complexity of the grid network. This paper proposes a new model of a single phase grid connected renewable energy source using the Harmonic State Space modeling approach, which is able to identify such problems and the model can be extended to be applied in the multiple connected converter Analysis. The modeling results show the different harmonic impedance matrixes, where that represents the harmonic coupling characteristic as well as the different Instability characteristics. The theoretical modeling and Analysis are verified by simulations and also experimental results.