Pub Date : 2022-03-01DOI: 10.1177/17568277221088422
J. G. V. von Saldern, J. M. Reumschüssel, J. P. Beuth, C. O. Paschereit, K. Oberleithner
Operation under stable conditions is an important prerequisite for gas turbine safety. While recent studies have focused primarily on acoustic design to avoid thermoacoustic instabilities, in the present study we shift the focus to improving stability margins by flame transfer function (FTF) modification. The flame transfer function of premixed flames is affected by various mechanisms such as variations in equivalence ratio, swirl fluctuations and shear layer instabilities. These mechanisms can be influenced by modifying parameters such as fuel distribution, injection location, swirl number or gas composition. Based on the Nyquist stability method we formulate criteria for how and at what frequencies the flame transfer function needs to be modified, in order to increase the stability margins of a thermoacoustic system. Gain and phase margin as well as the sensitivity function serve as measures of stability. The criteria are limited to single frequencies, which allows experimental FTF optimization with manageable effort. In the second part of this study it is shown that the Nyquist method can also be used as an efficient and compact way to determine whether the uncertainties of subsystems can affect the overall stability, without requiring eigenvalue calculations.
{"title":"Robust combustor design based on flame transfer function modification","authors":"J. G. V. von Saldern, J. M. Reumschüssel, J. P. Beuth, C. O. Paschereit, K. Oberleithner","doi":"10.1177/17568277221088422","DOIUrl":"https://doi.org/10.1177/17568277221088422","url":null,"abstract":"Operation under stable conditions is an important prerequisite for gas turbine safety. While recent studies have focused primarily on acoustic design to avoid thermoacoustic instabilities, in the present study we shift the focus to improving stability margins by flame transfer function (FTF) modification. The flame transfer function of premixed flames is affected by various mechanisms such as variations in equivalence ratio, swirl fluctuations and shear layer instabilities. These mechanisms can be influenced by modifying parameters such as fuel distribution, injection location, swirl number or gas composition. Based on the Nyquist stability method we formulate criteria for how and at what frequencies the flame transfer function needs to be modified, in order to increase the stability margins of a thermoacoustic system. Gain and phase margin as well as the sensitivity function serve as measures of stability. The criteria are limited to single frequencies, which allows experimental FTF optimization with manageable effort. In the second part of this study it is shown that the Nyquist method can also be used as an efficient and compact way to determine whether the uncertainties of subsystems can affect the overall stability, without requiring eigenvalue calculations.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42672201","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 : 2022-03-01DOI: 10.1177/17568277221092987
T. Christou, B. Stelzner, N. Zarzalis
An appealing concept for jet engine combustors is the Lean Premixed Prevaporized (LPP) combustor, which operates at high pressures. The low NOx emissions achieved by lean combustion are one of the targets for modern aircraft engines. However, these types of combustors can introduce thermoacoustic instabilities that can potentially damage the engine and reduce its lifespan. Since the potential instabilities on the fuel spray characteristics, i.e. the spray mass flux, can affect the flame stability, the need arises to investigate the spray response under an unsteady airflow. For this study, a model prefilmer was experimentally investigated to produce a two-dimensional droplet flow without swirl flow. An acoustic forcing in the range of 100–500 Hz was introduced into the airflow, characterized by a hot wire Constant Temperature Anemometry (CTA) setup. Droplet characteristics, namely the droplet diameter distribution and velocity, were determined using a Phase Doppler Anemometry (PDA) setup, while the acquired data were phase-averaged in one period of the airflow oscillation. The influence of the excitation frequency and the air-to-liquid ratio (ALR) on the spray was studied: the spray responded to the acoustic excitation and therefore critical performance parameters, such as the spray mass flux, oscillated indicating potential problems regarding the flame stability.
{"title":"Spray response on a model prefilmer under unsteady airflows of various frequencies","authors":"T. Christou, B. Stelzner, N. Zarzalis","doi":"10.1177/17568277221092987","DOIUrl":"https://doi.org/10.1177/17568277221092987","url":null,"abstract":"An appealing concept for jet engine combustors is the Lean Premixed Prevaporized (LPP) combustor, which operates at high pressures. The low NOx emissions achieved by lean combustion are one of the targets for modern aircraft engines. However, these types of combustors can introduce thermoacoustic instabilities that can potentially damage the engine and reduce its lifespan. Since the potential instabilities on the fuel spray characteristics, i.e. the spray mass flux, can affect the flame stability, the need arises to investigate the spray response under an unsteady airflow. For this study, a model prefilmer was experimentally investigated to produce a two-dimensional droplet flow without swirl flow. An acoustic forcing in the range of 100–500 Hz was introduced into the airflow, characterized by a hot wire Constant Temperature Anemometry (CTA) setup. Droplet characteristics, namely the droplet diameter distribution and velocity, were determined using a Phase Doppler Anemometry (PDA) setup, while the acquired data were phase-averaged in one period of the airflow oscillation. The influence of the excitation frequency and the air-to-liquid ratio (ALR) on the spray was studied: the spray responded to the acoustic excitation and therefore critical performance parameters, such as the spray mass flux, oscillated indicating potential problems regarding the flame stability.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47686410","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 : 2022-03-01DOI: 10.1177/17568277221094760
Gregor Doehner, M. Haeringer, Camilo F. Silva
In this work we present a parsimonious set of ordinary differential equations (ODEs) that describes with satisfactory precision the linear and non-linear dynamics of a typical laminar premixed flame in time and frequency domain. The proposed model is characterized by two ODEs of second-order that can be interpreted as two coupled mass-spring-damper oscillators with a symmetric, nonlinear damping term. This non-linear term is identified as function of the rate of displacement following x 2 x ˙ . The model requires only four constants to be calibrated. This is achieved by carrying out an optimization procedure on one input and one output broadband signal obtained from high-fidelity numerical simulations (CFD). Note that the Transfer Function (FTF) or describing function (FDF) of the flame under investigation are not known a-priori, and therefore not used in the optimization procedure. Once the model is trained on CFD input and output time series, it is capable of recovering with quantitative accuracy the impulse response of the laminar flame under investigation and, hence, the corresponding frequency response (FTF). If fed with harmonic signals of different frequency and amplitude, the trained model is capable of retrieving with qualitative precision the flame describing function (FDF) of the studied flame. We show that the non-linear term x 2 x ˙ is essential for capturing the gain saturation for high amplitudes of the input signal. All results are validated against CFD data.
{"title":"Nonlinear flame response modelling by a parsimonious set of ordinary differential equations","authors":"Gregor Doehner, M. Haeringer, Camilo F. Silva","doi":"10.1177/17568277221094760","DOIUrl":"https://doi.org/10.1177/17568277221094760","url":null,"abstract":"In this work we present a parsimonious set of ordinary differential equations (ODEs) that describes with satisfactory precision the linear and non-linear dynamics of a typical laminar premixed flame in time and frequency domain. The proposed model is characterized by two ODEs of second-order that can be interpreted as two coupled mass-spring-damper oscillators with a symmetric, nonlinear damping term. This non-linear term is identified as function of the rate of displacement following x 2 x ˙ . The model requires only four constants to be calibrated. This is achieved by carrying out an optimization procedure on one input and one output broadband signal obtained from high-fidelity numerical simulations (CFD). Note that the Transfer Function (FTF) or describing function (FDF) of the flame under investigation are not known a-priori, and therefore not used in the optimization procedure. Once the model is trained on CFD input and output time series, it is capable of recovering with quantitative accuracy the impulse response of the laminar flame under investigation and, hence, the corresponding frequency response (FTF). If fed with harmonic signals of different frequency and amplitude, the trained model is capable of retrieving with qualitative precision the flame describing function (FDF) of the studied flame. We show that the non-linear term x 2 x ˙ is essential for capturing the gain saturation for high amplitudes of the input signal. All results are validated against CFD data.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42764036","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 : 2022-03-01DOI: 10.1177/17568277221084464
G. A. Mensah, Philipp Buschmann, A. Orchini
The spectrum of the thermoacoustic operator is governed by a nonlinear eigenvalue problem. A few different strategies have been proposed by the thermoacoustic community to tackle it and identify the frequencies and growth rates of thermoacoustic eigenmodes. These strategies typically require the use of iterative algorithms, which need an initial guess and are not necessarily guaranteed to converge to an eigenvalue. A quantitative comparison between the convergence properties of these methods has however never been addressed. By using adjoint-based sensitivity, in this study we derive an explicit formula that can be used to quantify the behaviour of an iterative method in the vicinity of an eigenvalue. In particular, we employ Banach’s fixed-point theorem to demonstrate that there exist thermoacoustic eigenvalues that cannot be identified by some of the iterative methods proposed in the literature, in particular fixed-point iterations, regardless of the accuracy of the initial guess provided. We then introduce a family of iterative methods known as Householder’s methods, of which Newton’s method is a special case. The coefficients needed to use these methods are explicitly derived by means of high-order adjoint-based perturbation theory. We demonstrate how these methods are always guaranteed to converge to the closest eigenvalue, provided that the initial guess is accurate enough. We also show numerically how the basin of attraction of the eigenvalues varies with the order of the employed Householder’s method.
{"title":"Iterative solvers for the thermoacoustic nonlinear eigenvalue problem and their convergence properties","authors":"G. A. Mensah, Philipp Buschmann, A. Orchini","doi":"10.1177/17568277221084464","DOIUrl":"https://doi.org/10.1177/17568277221084464","url":null,"abstract":"The spectrum of the thermoacoustic operator is governed by a nonlinear eigenvalue problem. A few different strategies have been proposed by the thermoacoustic community to tackle it and identify the frequencies and growth rates of thermoacoustic eigenmodes. These strategies typically require the use of iterative algorithms, which need an initial guess and are not necessarily guaranteed to converge to an eigenvalue. A quantitative comparison between the convergence properties of these methods has however never been addressed. By using adjoint-based sensitivity, in this study we derive an explicit formula that can be used to quantify the behaviour of an iterative method in the vicinity of an eigenvalue. In particular, we employ Banach’s fixed-point theorem to demonstrate that there exist thermoacoustic eigenvalues that cannot be identified by some of the iterative methods proposed in the literature, in particular fixed-point iterations, regardless of the accuracy of the initial guess provided. We then introduce a family of iterative methods known as Householder’s methods, of which Newton’s method is a special case. The coefficients needed to use these methods are explicitly derived by means of high-order adjoint-based perturbation theory. We demonstrate how these methods are always guaranteed to converge to the closest eigenvalue, provided that the initial guess is accurate enough. We also show numerically how the basin of attraction of the eigenvalues varies with the order of the employed Householder’s method.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42989478","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 : 2021-09-01DOI: 10.1177/17568277211055979
W. Hua, Zhang Xin-yu, Jiang Yu-long, Zhao Ling-yao
The fuel flow pattern in the fuel injection nozzle of diesel engine is a complex and changeable phenomenon, which is easily affected by various factors, bringing the differences of flow patterns between multiple injection cycles. To solve the above problem, a visual experimental platform of fuel injection nozzle was built, in which the 100 injection cycles of diesel engine on the same working condition were photographed via shadowgraphy to study the difference in fuel flow pattern in the nozzle by ensemble average processing method. The cyclic variation rate K of fuel flow pattern is defined. Results demonstrate that the fuel flow pattern tends to be the same in multiple fuel injection cycles, but there is a strong randomness at the starting of injection and after ending of injection; the K can be reduced by decreasing the injection pressure and the inclination angle of orifice, so that the fuel flow pattern in the nozzle tends to be consistent.
{"title":"Study on cyclic variation rate of fuel flow in the nozzle during fuel injection","authors":"W. Hua, Zhang Xin-yu, Jiang Yu-long, Zhao Ling-yao","doi":"10.1177/17568277211055979","DOIUrl":"https://doi.org/10.1177/17568277211055979","url":null,"abstract":"The fuel flow pattern in the fuel injection nozzle of diesel engine is a complex and changeable phenomenon, which is easily affected by various factors, bringing the differences of flow patterns between multiple injection cycles. To solve the above problem, a visual experimental platform of fuel injection nozzle was built, in which the 100 injection cycles of diesel engine on the same working condition were photographed via shadowgraphy to study the difference in fuel flow pattern in the nozzle by ensemble average processing method. The cyclic variation rate K of fuel flow pattern is defined. Results demonstrate that the fuel flow pattern tends to be the same in multiple fuel injection cycles, but there is a strong randomness at the starting of injection and after ending of injection; the K can be reduced by decreasing the injection pressure and the inclination angle of orifice, so that the fuel flow pattern in the nozzle tends to be consistent.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44800113","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 : 2021-09-01DOI: 10.1177/17568277221086261
F. Gant, A. Cuquel, M. Bothien
Modern gas turbines need to fulfil increasingly stringent emission targets on the one hand and exhibit outstanding operational and fuel flexibility on the other. Ansaldo Energia GT26 and GT36 gas turbine models address these requirements by employing a combustion system in which two lean premixed combustors are arranged in series. Due to the high inlet temperatures from the first stage, the second combustor stage predominantly relies on autoignition for flame stabilization. In this paper, the response of autoignition flames to temperature, pressure and velocity excitations is investigated. The gas turbine combustor geometry is represented by a backward-facing step. Based on the conservation equations an analytical model is derived by solving the linearized Rankine-Hugoniot conditions. This is a commonly used analytical approach to describe the relation of thermodynamic quantities up- and downstream of a propagation stabilized flame. In particular, the linearized Rankine-Hugoniot jump conditions are derived taking into account the presence of a moving discontinuity as well as upstream entropy inhomogeneities. The unsteady heat release rate of the flame is modelled as a linear superposition of flame transfer functions, accounting for velocity, pressure, and entropy disturbances, respectively. This results in a 3 × 3 flame transfer matrix relating both primitive acoustic variables and the temperature fluctuations across the flame. The obtained analytical expression is compared to large eddy simulations with excellent agreement. A discussion about the contribution of the single terms to the modelling effort is provided, with a focus on autoignition flames.
{"title":"Autoignition flame transfer matrix: Analytical model versus large eddy simulations","authors":"F. Gant, A. Cuquel, M. Bothien","doi":"10.1177/17568277221086261","DOIUrl":"https://doi.org/10.1177/17568277221086261","url":null,"abstract":"Modern gas turbines need to fulfil increasingly stringent emission targets on the one hand and exhibit outstanding operational and fuel flexibility on the other. Ansaldo Energia GT26 and GT36 gas turbine models address these requirements by employing a combustion system in which two lean premixed combustors are arranged in series. Due to the high inlet temperatures from the first stage, the second combustor stage predominantly relies on autoignition for flame stabilization. In this paper, the response of autoignition flames to temperature, pressure and velocity excitations is investigated. The gas turbine combustor geometry is represented by a backward-facing step. Based on the conservation equations an analytical model is derived by solving the linearized Rankine-Hugoniot conditions. This is a commonly used analytical approach to describe the relation of thermodynamic quantities up- and downstream of a propagation stabilized flame. In particular, the linearized Rankine-Hugoniot jump conditions are derived taking into account the presence of a moving discontinuity as well as upstream entropy inhomogeneities. The unsteady heat release rate of the flame is modelled as a linear superposition of flame transfer functions, accounting for velocity, pressure, and entropy disturbances, respectively. This results in a 3 × 3 flame transfer matrix relating both primitive acoustic variables and the temperature fluctuations across the flame. The obtained analytical expression is compared to large eddy simulations with excellent agreement. A discussion about the contribution of the single terms to the modelling effort is provided, with a focus on autoignition flames.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46951244","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 : 2021-09-01DOI: 10.1177/17568277211059073
A. Osorio, X. Tauzia, A. Maiboom
Diesel engines are becoming smaller as technology advances, which means that the fuel spray (or jet) interacts with the cylinder walls before combustion starts. Most fuel injection 1D models (especially for diesel fuel) do not consider this interaction. Therefore, a wall-jet sub-model was created on an Eulerian 1D diesel spray model. It was calibrated using data from the literature and validated with experimental data from a fuel spray impacting a plate in a constant volume combustion chamber. Results show that the spray moving along the wall has a higher mixing rate but less penetration as an equivalent free jet, therefore they show a similar volume. Spray-wall interaction creates a stagnation zone right before the impact with the wall, and friction of the jet with the wall is relatively low. All these phenomena are well captured by the wall-jet sub-model.
{"title":"Development of a wall jet model dedicated to 1D combustion modelling for CI engines","authors":"A. Osorio, X. Tauzia, A. Maiboom","doi":"10.1177/17568277211059073","DOIUrl":"https://doi.org/10.1177/17568277211059073","url":null,"abstract":"Diesel engines are becoming smaller as technology advances, which means that the fuel spray (or jet) interacts with the cylinder walls before combustion starts. Most fuel injection 1D models (especially for diesel fuel) do not consider this interaction. Therefore, a wall-jet sub-model was created on an Eulerian 1D diesel spray model. It was calibrated using data from the literature and validated with experimental data from a fuel spray impacting a plate in a constant volume combustion chamber. Results show that the spray moving along the wall has a higher mixing rate but less penetration as an equivalent free jet, therefore they show a similar volume. Spray-wall interaction creates a stagnation zone right before the impact with the wall, and friction of the jet with the wall is relatively low. All these phenomena are well captured by the wall-jet sub-model.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44323631","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 : 2021-09-01DOI: 10.1177/17568277211057360
S. El-Sayed
This paper investigated the critical ignition conditions of combustible gas containing liquid fuel droplets. The analysis is done based on the criteria of the thermal explosion theory. It includes analytical and numerical solutions of modeling equations of fuel droplets heating and evaporation by convection and radiation from the surrounding reactive hot gas. The exothermic reaction is usually modeled as a single-step reaction obeying an Arrhenius temperature dependence. The thermal conductivity of the fuel droplet is dependent on temperature. The analytical solution produced relations between the main critical characteristic parameters in all planes of the solution. The results obtained from investigating the effect of the characteristic parameters on the explosion behavior of gas and fuel droplets and the thermal radiation proved that both of them are significant. The study proved that the criticality definitions of the thermal explosion of a single-phase system can be used effectively and efficiently to determine the critical conditions of a multi-phase system. Finally, the application of the numerical solutions of the modeling equations was used to analyze the explosion characteristics of a diesel fuel spray system.
{"title":"Thermal explosion characteristics of a combustible gas containing fuel droplets","authors":"S. El-Sayed","doi":"10.1177/17568277211057360","DOIUrl":"https://doi.org/10.1177/17568277211057360","url":null,"abstract":"This paper investigated the critical ignition conditions of combustible gas containing liquid fuel droplets. The analysis is done based on the criteria of the thermal explosion theory. It includes analytical and numerical solutions of modeling equations of fuel droplets heating and evaporation by convection and radiation from the surrounding reactive hot gas. The exothermic reaction is usually modeled as a single-step reaction obeying an Arrhenius temperature dependence. The thermal conductivity of the fuel droplet is dependent on temperature. The analytical solution produced relations between the main critical characteristic parameters in all planes of the solution. The results obtained from investigating the effect of the characteristic parameters on the explosion behavior of gas and fuel droplets and the thermal radiation proved that both of them are significant. The study proved that the criticality definitions of the thermal explosion of a single-phase system can be used effectively and efficiently to determine the critical conditions of a multi-phase system. Finally, the application of the numerical solutions of the modeling equations was used to analyze the explosion characteristics of a diesel fuel spray system.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42114013","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 : 2021-07-01DOI: 10.1177/17568277221139974
Ushnish Sengupta, Gunther Waxenegger-Wilfing, J. Hardi, M. Juniper
We present a method that combines multiple sensory modalities in a rocket thrust chamber to predict impending thermoacoustic instabilities with uncertainties. This is accomplished by training an autoregressive Bayesian neural network model that forecasts the future amplitude of the dynamic pressure time series, using multiple sensor measurements (injector pressure/ temperature measurements, static chamber pressure, high-frequency dynamic pressure measurements, high-frequency OH* chemiluminescence measurements) and future flow rate control signals as input. The method is validated using experimental data from a representative cryogenic research thrust chamber. The Bayesian nature of our algorithms allows us to work with a dataset whose size is restricted by the expense of each experimental run, without making overconfident extrapolations. We find that the networks are able to accurately forecast the evolution of the pressure amplitude and anticipate instability events on unseen experimental runs 500 milliseconds in advance. We compare the predictive accuracy of multiple models using different combinations of sensor inputs. We find that the high-frequency dynamic pressure signal is particularly informative. We also use the technique of integrated gradients to interpret the influence of different sensor inputs on the model prediction. The negative log-likelihood of data points in the test dataset indicates that prediction uncertainties are well-characterized by our model and simulating a sensor failure event results in a dramatic increase in the epistemic component of the uncertainty, as would be expected when a Bayesian method encounters unfamiliar, out-of-distribution inputs.
{"title":"Forecasting thermoacoustic instabilities in liquid propellant rocket engines using multimodal Bayesian deep learning","authors":"Ushnish Sengupta, Gunther Waxenegger-Wilfing, J. Hardi, M. Juniper","doi":"10.1177/17568277221139974","DOIUrl":"https://doi.org/10.1177/17568277221139974","url":null,"abstract":"We present a method that combines multiple sensory modalities in a rocket thrust chamber to predict impending thermoacoustic instabilities with uncertainties. This is accomplished by training an autoregressive Bayesian neural network model that forecasts the future amplitude of the dynamic pressure time series, using multiple sensor measurements (injector pressure/ temperature measurements, static chamber pressure, high-frequency dynamic pressure measurements, high-frequency OH* chemiluminescence measurements) and future flow rate control signals as input. The method is validated using experimental data from a representative cryogenic research thrust chamber. The Bayesian nature of our algorithms allows us to work with a dataset whose size is restricted by the expense of each experimental run, without making overconfident extrapolations. We find that the networks are able to accurately forecast the evolution of the pressure amplitude and anticipate instability events on unseen experimental runs 500 milliseconds in advance. We compare the predictive accuracy of multiple models using different combinations of sensor inputs. We find that the high-frequency dynamic pressure signal is particularly informative. We also use the technique of integrated gradients to interpret the influence of different sensor inputs on the model prediction. The negative log-likelihood of data points in the test dataset indicates that prediction uncertainties are well-characterized by our model and simulating a sensor failure event results in a dramatic increase in the epistemic component of the uncertainty, as would be expected when a Bayesian method encounters unfamiliar, out-of-distribution inputs.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45354096","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 : 2021-06-01DOI: 10.1177/17568277211021322
P. M. de Oliveira, M. Sitte, M. Zedda, A. Giusti, E. Mastorakos
A physics-based, low-order ignition model is used to assess the ignition performance of a kerosene-fueled gas-turbine combustor under high-altitude relight conditions. The ignition model used in this study is based on the motion of virtual flame particles and their extinction according to a Karlovitz number criterion, and a stochastic procedure is used to account for the effects of spray polydispersity on the flame’s extinction behavior. The effects of large droplets arising from poor fuel atomization at sub-idle conditions are then investigated in the context of the model parameters and the combustor’s ignition behavior. For that, a Reynolds-averaged Navier-Stokes simulation of the cold flow in the combustor was performed and used as an input for the ignition model. Ignition was possible with a Sauter mean diameter (SMD) of 50 μm, and was enhanced by increasing the spark volume. Although doubling the spark volume at larger SMDs (75 and 100 μm) resulted in the suppression of short-mode failure events, ignition was not achieved due to a reduction of the effective flammable volume in the combustor. Overall, a lower ignition probability is obtained when using the stochastic procedure for the spray, which is to be expected due to the additional detrimental effects associated with poor spray atomisation and high polydispersity.
{"title":"Low-order modeling of high-altitude relight of jet engine combustors","authors":"P. M. de Oliveira, M. Sitte, M. Zedda, A. Giusti, E. Mastorakos","doi":"10.1177/17568277211021322","DOIUrl":"https://doi.org/10.1177/17568277211021322","url":null,"abstract":"A physics-based, low-order ignition model is used to assess the ignition performance of a kerosene-fueled gas-turbine combustor under high-altitude relight conditions. The ignition model used in this study is based on the motion of virtual flame particles and their extinction according to a Karlovitz number criterion, and a stochastic procedure is used to account for the effects of spray polydispersity on the flame’s extinction behavior. The effects of large droplets arising from poor fuel atomization at sub-idle conditions are then investigated in the context of the model parameters and the combustor’s ignition behavior. For that, a Reynolds-averaged Navier-Stokes simulation of the cold flow in the combustor was performed and used as an input for the ignition model. Ignition was possible with a Sauter mean diameter (SMD) of 50 μm, and was enhanced by increasing the spark volume. Although doubling the spark volume at larger SMDs (75 and 100 μm) resulted in the suppression of short-mode failure events, ignition was not achieved due to a reduction of the effective flammable volume in the combustor. Overall, a lower ignition probability is obtained when using the stochastic procedure for the spray, which is to be expected due to the additional detrimental effects associated with poor spray atomisation and high polydispersity.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/17568277211021322","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65533080","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：