Pub Date : 2018-12-01DOI: 10.1177/1756827718809570
A. Bigongiari, M. Heckl
In this paper, we will present a fast prediction tool based on a one-dimensional Green's function approach that can be used to bypass numerically expensive computational fluid dynamics simulations. The Green’s function approach has the advantage of providing a clear picture of the physics behind the generation and evolution of combustion instabilities. In addition, the method allows us to perform a modal analysis; single acoustic modes can be treated in isolation or in combination with other modes. In this article, we will investigate the role of higher-order modes in determining the stability of the system. We will initially produce the stability maps for the first and second mode separately. Then the time history of the perturbation will be computed, where both the modes are present. The flame will be modelled by a generic Flame Describing Function, i.e. by an amplitude-dependent Flame Transfer Function. The time-history calculations show the evolution of the two modes resulting from an initial perturbation; both transient and limit-cycle oscillations are revealed. Our study represents a first step towards the modelling of nonlinearity and non-normality in combustion processes.
{"title":"Analysis of the interaction of thermoacoustic modes with a Green’s function approach","authors":"A. Bigongiari, M. Heckl","doi":"10.1177/1756827718809570","DOIUrl":"https://doi.org/10.1177/1756827718809570","url":null,"abstract":"In this paper, we will present a fast prediction tool based on a one-dimensional Green's function approach that can be used to bypass numerically expensive computational fluid dynamics simulations. The Green’s function approach has the advantage of providing a clear picture of the physics behind the generation and evolution of combustion instabilities. In addition, the method allows us to perform a modal analysis; single acoustic modes can be treated in isolation or in combination with other modes. In this article, we will investigate the role of higher-order modes in determining the stability of the system. We will initially produce the stability maps for the first and second mode separately. Then the time history of the perturbation will be computed, where both the modes are present. The flame will be modelled by a generic Flame Describing Function, i.e. by an amplitude-dependent Flame Transfer Function. The time-history calculations show the evolution of the two modes resulting from an initial perturbation; both transient and limit-cycle oscillations are revealed. Our study represents a first step towards the modelling of nonlinearity and non-normality in combustion processes.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718809570","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42983552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1177/1756827717728056
S. Gopinathan, Dmytro Iurashev, A. Bigongiari, M. Heckl
In the present work, we formulate a new method to represent a given Flame Describing Function by analytical expressions. The underlying idea is motivated by the observation that different types of perturbations in a burner travel with different speeds and that the arrival of a perturbation at the flame is spread out over time. We develop an analytical model for the Flame Describing Function, which consists of a superposition of several Gaussians, each characterised by three amplitude-dependent quantities: central time-lag, peak value and standard deviation. These quantities are treated as fitting parameters, and they are deduced from the original Flame Describing Function by using error minimisation and nonlinear optimisation techniques. The amplitude-dependence of the fitting parameters is also represented analytically (by linear or quadratic functions). We test our method by using it to make stability predictions for a burner with well-documented stability behaviour (Noiray's matrix burner). This is done in the time-domain with a tailored Green's function approach.
{"title":"Nonlinear analytical flame models with amplitude-dependent time-lag distributions","authors":"S. Gopinathan, Dmytro Iurashev, A. Bigongiari, M. Heckl","doi":"10.1177/1756827717728056","DOIUrl":"https://doi.org/10.1177/1756827717728056","url":null,"abstract":"In the present work, we formulate a new method to represent a given Flame Describing Function by analytical expressions. The underlying idea is motivated by the observation that different types of perturbations in a burner travel with different speeds and that the arrival of a perturbation at the flame is spread out over time. We develop an analytical model for the Flame Describing Function, which consists of a superposition of several Gaussians, each characterised by three amplitude-dependent quantities: central time-lag, peak value and standard deviation. These quantities are treated as fitting parameters, and they are deduced from the original Flame Describing Function by using error minimisation and nonlinear optimisation techniques. The amplitude-dependence of the fitting parameters is also represented analytically (by linear or quadratic functions). We test our method by using it to make stability predictions for a burner with well-documented stability behaviour (Noiray's matrix burner). This is done in the time-domain with a tailored Green's function approach.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717728056","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42926930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1177/1756827718808076
M. Heckl
This special issue features a selection of research papers produced by the project TANGO – an initial training network (ITN) with an international consortium of seven academic and five industrial partners. TANGO is the acronym for ‘Thermoacoustic and Aeroacoustic Nonlinearities in Green combustors with Orifice structures’. During the four years of its lifetime (2012–2016), a total of 15 young researchers were funded by this network; the majority of them had three-year PhD positions. Further information about TANGO (such as the consortium members, research tasks and publications) can be found on the project website http://www.scm.keele.ac.uk/Tango/ As the title of the project suggests, thermoacoustics and aeroacoustics were the main areas of scientific enquiry. These disciplines are fundamental for the understanding of thermoacoustic instabilities. The basic mechanism driving a thermoacoustic instability is a three-way interaction between the heat release from a heat source (typically a flame), the acoustic field in the cavity that houses the heat source, and aerodynamic structures (such as vortices shed from an orifice and then impinging on the flame). This basic mechanism occurs in tandem with other physical and chemical processes, leading to a complex web of interactions, most of which are nonlinear. Research to unravel this web has been going on intensively for decades, but there are still a lot of open questions. For environmental reasons, it is important to make combustors ‘green’, i.e. to develop combustion systems that have low levels of pollutant emission. This is achieved by lean premixed combustion. Unfortunately, this form of combustion is particularly prone to thermoacoustic instabilities. They manifest themselves by intense pressure oscillations, excessive structural vibrations, fatigue and even catastrophic damage to combustor hardware. Until thermoacoustic instabilities are fully understood, they are an obstacle for the development of green combustion systems. The aim of TANGO was to develop a large amount of new understanding so as to predict under what conditions such instabilities occur, what amplitudes are reached, and – most importantly – how the instabilities can be prevented. The research was interdisciplinary and involved numerical, analytical and experimental approaches. It can be roughly divided into two parts: thermoacoustics and aeroacoustics, although there was considerable interaction across this divide. Two review papers, one focussing on thermoacoustics and the other one on aeroacoustics, will appear in a forthcoming issue of this journal. The papers in this issue have undergone a rigorous review process. They give highlights of TANGO’s research activities on a range of topics, including
{"title":"Advances by the Marie Curie project TANGO in thermoacoustics and aeroacoustics","authors":"M. Heckl","doi":"10.1177/1756827718808076","DOIUrl":"https://doi.org/10.1177/1756827718808076","url":null,"abstract":"This special issue features a selection of research papers produced by the project TANGO – an initial training network (ITN) with an international consortium of seven academic and five industrial partners. TANGO is the acronym for ‘Thermoacoustic and Aeroacoustic Nonlinearities in Green combustors with Orifice structures’. During the four years of its lifetime (2012–2016), a total of 15 young researchers were funded by this network; the majority of them had three-year PhD positions. Further information about TANGO (such as the consortium members, research tasks and publications) can be found on the project website http://www.scm.keele.ac.uk/Tango/ As the title of the project suggests, thermoacoustics and aeroacoustics were the main areas of scientific enquiry. These disciplines are fundamental for the understanding of thermoacoustic instabilities. The basic mechanism driving a thermoacoustic instability is a three-way interaction between the heat release from a heat source (typically a flame), the acoustic field in the cavity that houses the heat source, and aerodynamic structures (such as vortices shed from an orifice and then impinging on the flame). This basic mechanism occurs in tandem with other physical and chemical processes, leading to a complex web of interactions, most of which are nonlinear. Research to unravel this web has been going on intensively for decades, but there are still a lot of open questions. For environmental reasons, it is important to make combustors ‘green’, i.e. to develop combustion systems that have low levels of pollutant emission. This is achieved by lean premixed combustion. Unfortunately, this form of combustion is particularly prone to thermoacoustic instabilities. They manifest themselves by intense pressure oscillations, excessive structural vibrations, fatigue and even catastrophic damage to combustor hardware. Until thermoacoustic instabilities are fully understood, they are an obstacle for the development of green combustion systems. The aim of TANGO was to develop a large amount of new understanding so as to predict under what conditions such instabilities occur, what amplitudes are reached, and – most importantly – how the instabilities can be prevented. The research was interdisciplinary and involved numerical, analytical and experimental approaches. It can be roughly divided into two parts: thermoacoustics and aeroacoustics, although there was considerable interaction across this divide. Two review papers, one focussing on thermoacoustics and the other one on aeroacoustics, will appear in a forthcoming issue of this journal. The papers in this issue have undergone a rigorous review process. They give highlights of TANGO’s research activities on a range of topics, including","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718808076","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43871860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-01DOI: 10.1177/1756827717747201
Alp Albayrak, Deniz A. Bezgin, W. Polifke
Acoustic waves passing through a swirler generate inertial waves in rotating flow. In the present study, the response of a premixed flame to an inertial wave is scrutinized, with emphasis on the fundamental fluid-dynamic and flame-kinematic interaction mechanism. The analysis relies on linearized reactive flow equations, with a two-part solution strategy implemented in a finite element framework: Firstly, the steady state, low-Mach number, Navier–Stokes equations with Arrhenius type one-step reaction mechanism are solved by Newton’s method. The flame impulse response is then computed by transient solution of the analytically linearized reactive flow equations in the time domain, with mean flow quantities provided by the steady-state solution. The corresponding flame transfer function is retrieved by fitting a finite impulse response model. This approach is validated against experiments for a perfectly premixed, lean, methane-air Bunsen flame, and then applied to a laminar swirling flame. This academic case serves to investigate in a generic manner the impact of an inertial wave on the flame response. The structure of the inertial wave is characterized by modal decomposition. It is shown that axial and radial velocity fluctuations related to the eigenmodes of the inertial wave dominate the flame front modulations. The dispersive nature of the eigenmodes plays an important role in the flame response.
{"title":"Response of a swirl flame to inertial waves","authors":"Alp Albayrak, Deniz A. Bezgin, W. Polifke","doi":"10.1177/1756827717747201","DOIUrl":"https://doi.org/10.1177/1756827717747201","url":null,"abstract":"Acoustic waves passing through a swirler generate inertial waves in rotating flow. In the present study, the response of a premixed flame to an inertial wave is scrutinized, with emphasis on the fundamental fluid-dynamic and flame-kinematic interaction mechanism. The analysis relies on linearized reactive flow equations, with a two-part solution strategy implemented in a finite element framework: Firstly, the steady state, low-Mach number, Navier–Stokes equations with Arrhenius type one-step reaction mechanism are solved by Newton’s method. The flame impulse response is then computed by transient solution of the analytically linearized reactive flow equations in the time domain, with mean flow quantities provided by the steady-state solution. The corresponding flame transfer function is retrieved by fitting a finite impulse response model. This approach is validated against experiments for a perfectly premixed, lean, methane-air Bunsen flame, and then applied to a laminar swirling flame. This academic case serves to investigate in a generic manner the impact of an inertial wave on the flame response. The structure of the inertial wave is characterized by modal decomposition. It is shown that axial and radial velocity fluctuations related to the eigenmodes of the inertial wave dominate the flame front modulations. The dispersive nature of the eigenmodes plays an important role in the flame response.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717747201","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47104518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-11-18DOI: 10.1177/1756827718812519
S. De, A. Bhattacharya, S. Mondal, A. Mukhopadhyay, S. Sen
Lean blowout is one of the major challenges faced when the gas turbine combustors are operated with lean fuel–air mixture to meet the emission norm. We experimentally study the flame behavior and the dynamics of heat release rate fluctuations during a transition to lean blowout. The study comprising flame visualization and estimating several measures to predict lean blowout for both premixed and partially premixed flames (using fuel ports F1 to F5) in a swirl stabilized dump combustor. To that end, we acquire unsteady heat release rate in terms of CH* chemiluminescence obtained through a photomultiplier tube with a narrow band-pass filter. For evaluating different statistical measures, we use National Instrument Labview software while acquiring the heat release rate oscillations. For premixed and partially premixed flames, such measures and the flame behavior show a different and, in some cases, even opposite trends as lean blowout is approached. However, in both premixed and partially premixed flames, the mean and root mean square values of the heat release rate fluctuation decrease as we decrease the equivalence ratio. Further, we show that the value of mean frequency calculated using Hilbert transform of the heat release rate fluctuations is a good indicator of lean blowout. Apart from the early prediction of lean blowout, different statistics of heat release rate oscillations, such as kurtosis and skewness, are shown to identify only the occurrence of lean blowout for premixed (F1 and F2) and flames with lower level of premixing (F3). They are not useful for the flames with high levels of unmixedness like F4 and F5. On the other side, probability density function is seen useful for both premixed and partially premixed flames. In short, we present the relative importance of different measures stated earlier for the identification and early prediction of lean blowout for both premixed and partially premixed flames.
{"title":"Investigation of flame behavior and dynamics prior to lean blowout in a combustor with varying mixedness of reactants for the early detection of lean blowout","authors":"S. De, A. Bhattacharya, S. Mondal, A. Mukhopadhyay, S. Sen","doi":"10.1177/1756827718812519","DOIUrl":"https://doi.org/10.1177/1756827718812519","url":null,"abstract":"Lean blowout is one of the major challenges faced when the gas turbine combustors are operated with lean fuel–air mixture to meet the emission norm. We experimentally study the flame behavior and the dynamics of heat release rate fluctuations during a transition to lean blowout. The study comprising flame visualization and estimating several measures to predict lean blowout for both premixed and partially premixed flames (using fuel ports F1 to F5) in a swirl stabilized dump combustor. To that end, we acquire unsteady heat release rate in terms of CH* chemiluminescence obtained through a photomultiplier tube with a narrow band-pass filter. For evaluating different statistical measures, we use National Instrument Labview software while acquiring the heat release rate oscillations. For premixed and partially premixed flames, such measures and the flame behavior show a different and, in some cases, even opposite trends as lean blowout is approached. However, in both premixed and partially premixed flames, the mean and root mean square values of the heat release rate fluctuation decrease as we decrease the equivalence ratio. Further, we show that the value of mean frequency calculated using Hilbert transform of the heat release rate fluctuations is a good indicator of lean blowout. Apart from the early prediction of lean blowout, different statistics of heat release rate oscillations, such as kurtosis and skewness, are shown to identify only the occurrence of lean blowout for premixed (F1 and F2) and flames with lower level of premixing (F3). They are not useful for the flames with high levels of unmixedness like F4 and F5. On the other side, probability density function is seen useful for both premixed and partially premixed flames. In short, we present the relative importance of different measures stated earlier for the identification and early prediction of lean blowout for both premixed and partially premixed flames.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718812519","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41385823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-09-11DOI: 10.1177/1756827718799043
D. Rouwenhorst, J. Hermann, W. Polifke
In annular combustion systems, thermoacoustic eigenmodes can manifest as standing waves, traveling waves or some form in between. Which dynamic solution appears in a combustor depends on details, regarding the flow field and (unintentional) breaking of the cylindrical symmetry of the annular combustion system. When these details are unknown, the specific behavior cannot be predicted from the characteristics of a single burner. Due to the (nearly) degenerate nature of the acoustic solution, annular eigenmodes come in pairs with practically the same eigenfrequency. In order to identify the thermoacoustic modes, conventional analysis of a spectral peak from a measurement does not suffice, because the peak is a superposition of the two eigenmodes. A method has been proposed to identify the two eigenmodes of given azimuthal mode order from multiple simultaneous measurements around the circumference of the combustion system. Using output-only identification on the acoustic signals, it is possible to estimate the individual mode shapes, frequencies and growth rates of the co-existing eigenmode pair. In this work, the strategy is applied to experimental data from an annular combustor. A split in the growth rate pair is observed during stable operation, depending on the equivalence ratio and flame-to-flame distance. It shows that in situ identification of annular thermoacoustics can reveal subtle dynamic effects, which is useful for testing and online monitoring of annular combustors. The moment when instability occurs can be foreseen under prevailing conditions, with simultaneous identification of the azimuthal mode structure.
{"title":"In situ identification strategy of thermoacoustic stability in annular combustors","authors":"D. Rouwenhorst, J. Hermann, W. Polifke","doi":"10.1177/1756827718799043","DOIUrl":"https://doi.org/10.1177/1756827718799043","url":null,"abstract":"In annular combustion systems, thermoacoustic eigenmodes can manifest as standing waves, traveling waves or some form in between. Which dynamic solution appears in a combustor depends on details, regarding the flow field and (unintentional) breaking of the cylindrical symmetry of the annular combustion system. When these details are unknown, the specific behavior cannot be predicted from the characteristics of a single burner. Due to the (nearly) degenerate nature of the acoustic solution, annular eigenmodes come in pairs with practically the same eigenfrequency. In order to identify the thermoacoustic modes, conventional analysis of a spectral peak from a measurement does not suffice, because the peak is a superposition of the two eigenmodes. A method has been proposed to identify the two eigenmodes of given azimuthal mode order from multiple simultaneous measurements around the circumference of the combustion system. Using output-only identification on the acoustic signals, it is possible to estimate the individual mode shapes, frequencies and growth rates of the co-existing eigenmode pair. In this work, the strategy is applied to experimental data from an annular combustor. A split in the growth rate pair is observed during stable operation, depending on the equivalence ratio and flame-to-flame distance. It shows that in situ identification of annular thermoacoustics can reveal subtle dynamic effects, which is useful for testing and online monitoring of annular combustors. The moment when instability occurs can be foreseen under prevailing conditions, with simultaneous identification of the azimuthal mode structure.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718799043","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48567123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-08-31DOI: 10.1177/1756827718791921
Moritz Lipperheide, M. Gassner, Frank Weidner, S. Bernero, M. Wirsum
Emission measurements are a valuable source of information regarding the condition of gas turbine combustors. Aging of the hot gas path components can lead to an emission increase, which may ultimately require a readjustment of operational settings and accordingly impacts plant availability and maintenance. While NOx emissions may become crucial in high flame temperatures at full load, carbon monoxide emissions typically restrict low-load operation, which electricity markets demand more frequently due to the increasing penetration of intermittent renewable power. This paper presents a semiempirical carbon monoxide model that allows for quantifying the evolution of carbon monoxide emissions for GT24/GT26 heavy-duty gas turbines in commercial long-term operation. Input parameters to the derived carbon monoxide model are either directly measured or reconstructed by virtual measurements based on a simplified engine model. The method is developed with commissioning and operation data of three different gas turbines of GE’s GT24/GT26 fleet and validated over a total of 8.5 years of observation. Aging is accounted for by incorporating control sensor deviation and the formation of cold spots in the combustor into the semiempirical model. When these effects are taken into account, the carbon monoxide prediction is improved by up to 60% in terms of root mean square error of the log10(carbon monoxide) values compared to a benchmark case without consideration of aging.
{"title":"Long-term carbon monoxide emission behavior of heavy-duty gas turbines: An approach for model-based monitoring and diagnostics","authors":"Moritz Lipperheide, M. Gassner, Frank Weidner, S. Bernero, M. Wirsum","doi":"10.1177/1756827718791921","DOIUrl":"https://doi.org/10.1177/1756827718791921","url":null,"abstract":"Emission measurements are a valuable source of information regarding the condition of gas turbine combustors. Aging of the hot gas path components can lead to an emission increase, which may ultimately require a readjustment of operational settings and accordingly impacts plant availability and maintenance. While NOx emissions may become crucial in high flame temperatures at full load, carbon monoxide emissions typically restrict low-load operation, which electricity markets demand more frequently due to the increasing penetration of intermittent renewable power. This paper presents a semiempirical carbon monoxide model that allows for quantifying the evolution of carbon monoxide emissions for GT24/GT26 heavy-duty gas turbines in commercial long-term operation. Input parameters to the derived carbon monoxide model are either directly measured or reconstructed by virtual measurements based on a simplified engine model. The method is developed with commissioning and operation data of three different gas turbines of GE’s GT24/GT26 fleet and validated over a total of 8.5 years of observation. Aging is accounted for by incorporating control sensor deviation and the formation of cold spots in the combustor into the semiempirical model. When these effects are taken into account, the carbon monoxide prediction is improved by up to 60% in terms of root mean square error of the log10(carbon monoxide) values compared to a benchmark case without consideration of aging.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718791921","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49129695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-07-26DOI: 10.1177/1756827718789066
Luck Peerlings, F. Bake, Susann Boij, H. Bodén
To be able to compare the measured scattering matrices with model predictions, the quality of the measurements has to be known. Uncertainty analyses are invaluable to assess and improve the quality of measurement results in terms of accuracy and precision. Linear analyses are widespread, computationally fast and give information of the contribution of each error source to the overall measurement uncertainty; however, they cannot be applied in every situation. The purpose of this study is to determine if linear methods can be used to assess the quality of acoustic scattering matrices. The uncertainty in measured scattering matrices is assessed using a linear uncertainty analysis and the results are compared against Monte-Carlo simulations. It is shown that for plane waves, a linear uncertainty analysis, applied to the wave decomposition method, gives correct results when three conditions are satisfied. For higher order mode measurements, the number of conditions that have to be satisfied increases rapidly and the linear analysis becomes an unsuitable choice to determine the uncertainty on the scattering matrix coefficients. As the linear uncertainty analysis is most suitable for the plane wave range, an alternative linear method to assess the quality of the measurements is investigated. This method, based on matrix perturbation theory, gives qualitative information in the form of partial condition numbers and the implementation is straightforward. Using the alternative method, the measurements of higher order modes are analyzed and the observed difference in the measured reflection coefficients for different excitation conditions is explained by the disparity in modal amplitudes.
{"title":"Assessing the stochastic error of acoustic scattering matrices using linear methods","authors":"Luck Peerlings, F. Bake, Susann Boij, H. Bodén","doi":"10.1177/1756827718789066","DOIUrl":"https://doi.org/10.1177/1756827718789066","url":null,"abstract":"To be able to compare the measured scattering matrices with model predictions, the quality of the measurements has to be known. Uncertainty analyses are invaluable to assess and improve the quality of measurement results in terms of accuracy and precision. Linear analyses are widespread, computationally fast and give information of the contribution of each error source to the overall measurement uncertainty; however, they cannot be applied in every situation. The purpose of this study is to determine if linear methods can be used to assess the quality of acoustic scattering matrices. The uncertainty in measured scattering matrices is assessed using a linear uncertainty analysis and the results are compared against Monte-Carlo simulations. It is shown that for plane waves, a linear uncertainty analysis, applied to the wave decomposition method, gives correct results when three conditions are satisfied. For higher order mode measurements, the number of conditions that have to be satisfied increases rapidly and the linear analysis becomes an unsuitable choice to determine the uncertainty on the scattering matrix coefficients. As the linear uncertainty analysis is most suitable for the plane wave range, an alternative linear method to assess the quality of the measurements is investigated. This method, based on matrix perturbation theory, gives qualitative information in the form of partial condition numbers and the implementation is straightforward. Using the alternative method, the measurements of higher order modes are analyzed and the observed difference in the measured reflection coefficients for different excitation conditions is explained by the disparity in modal amplitudes.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718789066","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47198933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-07-13DOI: 10.1177/1756827718785851
Rohan M. Gejji, Cheng Huang, C. Fugger, Changjin Yoon, W. Anderson
Self-excited combustion dynamics in a liquid-fueled lean direct injection combustor at high pressure (1 MPa) are described. Studied variables include combustor and air plenum length, inlet air temperature, equivalence ratio, fuel nozzle location, and fuel composition. Measured pressure oscillations were dependent on combustor geometry and ranged from about 1% of mean chamber pressure at low equivalence ratio, up to 20% at high equivalence ratio. In the most unstable cases, strong pressure modes were measured throughout the frequency spectrum including a band around 1.2–1.5 kHz representing the 4th longitudinal mode, and another band around 7 kHz. The oscillation amplitudes have a non-monotonic dependency on air temperature, and are affected by the placement of the fuel nozzle relative to the throat of the subsonic swirling air flow. The parametric survey provides a rich dataset suitable for validating high-fidelity simulations and their subsequent use in analyzing and interpreting the complex combustion dynamics.
{"title":"Parametric investigation of combustion instabilities in a single-element lean direct injection combustor","authors":"Rohan M. Gejji, Cheng Huang, C. Fugger, Changjin Yoon, W. Anderson","doi":"10.1177/1756827718785851","DOIUrl":"https://doi.org/10.1177/1756827718785851","url":null,"abstract":"Self-excited combustion dynamics in a liquid-fueled lean direct injection combustor at high pressure (1 MPa) are described. Studied variables include combustor and air plenum length, inlet air temperature, equivalence ratio, fuel nozzle location, and fuel composition. Measured pressure oscillations were dependent on combustor geometry and ranged from about 1% of mean chamber pressure at low equivalence ratio, up to 20% at high equivalence ratio. In the most unstable cases, strong pressure modes were measured throughout the frequency spectrum including a band around 1.2–1.5 kHz representing the 4th longitudinal mode, and another band around 7 kHz. The oscillation amplitudes have a non-monotonic dependency on air temperature, and are affected by the placement of the fuel nozzle relative to the throat of the subsonic swirling air flow. The parametric survey provides a rich dataset suitable for validating high-fidelity simulations and their subsequent use in analyzing and interpreting the complex combustion dynamics.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718785851","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41408922","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-07-02DOI: 10.1177/1756827718782884
N. Hosseini, V. Kornilov, I. Lopéz Arteaga, W. Polifke, O. Teerling, L. D. de Goey
The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.
{"title":"Intrinsic thermoacoustic modes and their interplay with acoustic modes in a Rijke burner","authors":"N. Hosseini, V. Kornilov, I. Lopéz Arteaga, W. Polifke, O. Teerling, L. D. de Goey","doi":"10.1177/1756827718782884","DOIUrl":"https://doi.org/10.1177/1756827718782884","url":null,"abstract":"The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2018-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718782884","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48080306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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