Pedro Romero Vega, T. Hofmeister, Gerrit Heilmann, C. Hirsch, T. Sattelmayer
The linearized Euler equations (LEE) provide an accurate — yet computationally efficient — description of propagation and damping of acoustic waves in geometrically complex, non-uniform reactive mean flows like those found in gas turbine combustion chambers. However, direct application of the LEE to perfectly premixed combustors with highly turbulent flows overestimates entropy waves as the LEE solution inherently contains coupled acoustic, vortical and entropy modes. In the present work, the LEE are decomposed into isentropic and non-isentropic parts ultimately obtaining a simplified set of isentropic LEE, in which only acoustic and vortical modes propagate. In the isentropic LEE, only continuity and momentum equations need to be solved. The energy equation is replaced by the isentropic relation between acoustic pressure and density. From the decomposition, the unsteady heat release term, which acts as a source in the energy equation, naturally arises as a source in the continuity equation. This way, the thermoacoustic coupling is still preserved in the isentropic formulation. The derived isentropic set of equations is first tested with a one-dimensional benchmark configuration consisting of a mean flow temperature jump, non-uniform mean flow velocity and unsteady heat release sources. Solutions of the non-isentropic and isentropic set of LEE are compared and the avoidance of entropy waves proved. Finally, isentropic LEE are used for reproducing the frequency of the self-excited first transversal mode of a lab-scale swirl-stabilized premixed combustor. Furthermore, isentropic and non-isentropic LEE solutions are compared. The non-isentropic LEE yield too high levels of entropy at the combustor exit that may explain the increased damping rate of the non-isentropic LEE solution compared to the isentropic LEE solution. This shows the relevance of isentropic LEE for correctly predicting thermoacoustic stability limits at high frequencies in relevant industrial applications.
{"title":"Isentropic Formulation of the Linearized Euler Equations For Perfectly Premixed Combustion Systems","authors":"Pedro Romero Vega, T. Hofmeister, Gerrit Heilmann, C. Hirsch, T. Sattelmayer","doi":"10.1115/gt2021-60055","DOIUrl":"https://doi.org/10.1115/gt2021-60055","url":null,"abstract":"\u0000 The linearized Euler equations (LEE) provide an accurate — yet computationally efficient — description of propagation and damping of acoustic waves in geometrically complex, non-uniform reactive mean flows like those found in gas turbine combustion chambers. However, direct application of the LEE to perfectly premixed combustors with highly turbulent flows overestimates entropy waves as the LEE solution inherently contains coupled acoustic, vortical and entropy modes. In the present work, the LEE are decomposed into isentropic and non-isentropic parts ultimately obtaining a simplified set of isentropic LEE, in which only acoustic and vortical modes propagate. In the isentropic LEE, only continuity and momentum equations need to be solved. The energy equation is replaced by the isentropic relation between acoustic pressure and density. From the decomposition, the unsteady heat release term, which acts as a source in the energy equation, naturally arises as a source in the continuity equation. This way, the thermoacoustic coupling is still preserved in the isentropic formulation. The derived isentropic set of equations is first tested with a one-dimensional benchmark configuration consisting of a mean flow temperature jump, non-uniform mean flow velocity and unsteady heat release sources. Solutions of the non-isentropic and isentropic set of LEE are compared and the avoidance of entropy waves proved. Finally, isentropic LEE are used for reproducing the frequency of the self-excited first transversal mode of a lab-scale swirl-stabilized premixed combustor. Furthermore, isentropic and non-isentropic LEE solutions are compared. The non-isentropic LEE yield too high levels of entropy at the combustor exit that may explain the increased damping rate of the non-isentropic LEE solution compared to the isentropic LEE solution. This shows the relevance of isentropic LEE for correctly predicting thermoacoustic stability limits at high frequencies in relevant industrial applications.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114140374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To reach ambitious emission goals, the use of sustainable aviation fuels (SAFs) is a short-term option in current aero engines. The combustion of such fuels can, due to their low soot formation, have an impact on the thermal radiation inside the combustor. This in turn can affect the combustor liner temperatures, which are directly linked to the lifetime of the combustor. To study the impact of SAFs, the authors numerically simulated the flow inside a V2500 aero engine combustor using an OpenFOAM-based solver capable of capturing multi-physics phenomena such as combustion, conjugate heat transfer, thermal radiation and soot formation. The complex cooling system of the V2500 combustor makes the evaluation of the wall temperatures extremely challenging. To achieve results with the resources available, the authors replaced the densely packed pins inside the cooling channel with a boundary condition. This boundary condition was derived from a highly detailed simulation of a section of the cooling system. With this model reduction, the wall temperatures could be evaluated at four operating points. Back-to-back comparisons of the predicted wall temperatures with pictures of deteriorated combustor hardware out of the field operation reveals the plausibility of the numerical results. Finally, this numerical model was extended to include the effects of thermal radiation and soot formation. To predict the combustion of Jet-A, both models were used with settings derived from former validation simulations. The SAF combustion with extremely low sooting level was mimicked by deactivating the soot formation completely. The comparison of the radiation source term reveals — as expected — locally a higher radiation emission in areas where soot is formed in the combustor. As consequence, this leads to higher net radiative heat flux into the combustor liners. However, due to its minor importance in the overall energy balance, this change did not lead to significantly different liner temperatures.
{"title":"Influence of Alternative Fuels on the Liner Metal Temperatures in a V2500 Combustor","authors":"Lukas Schäflein, Ludovic de Guillebon, M. Konle","doi":"10.1115/gt2021-59443","DOIUrl":"https://doi.org/10.1115/gt2021-59443","url":null,"abstract":"\u0000 To reach ambitious emission goals, the use of sustainable aviation fuels (SAFs) is a short-term option in current aero engines. The combustion of such fuels can, due to their low soot formation, have an impact on the thermal radiation inside the combustor. This in turn can affect the combustor liner temperatures, which are directly linked to the lifetime of the combustor. To study the impact of SAFs, the authors numerically simulated the flow inside a V2500 aero engine combustor using an OpenFOAM-based solver capable of capturing multi-physics phenomena such as combustion, conjugate heat transfer, thermal radiation and soot formation.\u0000 The complex cooling system of the V2500 combustor makes the evaluation of the wall temperatures extremely challenging. To achieve results with the resources available, the authors replaced the densely packed pins inside the cooling channel with a boundary condition. This boundary condition was derived from a highly detailed simulation of a section of the cooling system. With this model reduction, the wall temperatures could be evaluated at four operating points. Back-to-back comparisons of the predicted wall temperatures with pictures of deteriorated combustor hardware out of the field operation reveals the plausibility of the numerical results.\u0000 Finally, this numerical model was extended to include the effects of thermal radiation and soot formation. To predict the combustion of Jet-A, both models were used with settings derived from former validation simulations. The SAF combustion with extremely low sooting level was mimicked by deactivating the soot formation completely. The comparison of the radiation source term reveals — as expected — locally a higher radiation emission in areas where soot is formed in the combustor. As consequence, this leads to higher net radiative heat flux into the combustor liners. However, due to its minor importance in the overall energy balance, this change did not lead to significantly different liner temperatures.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129742524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to predict the variation of the wall quenching distance of a premixed flame under different equivalence ratios and incoming flow velocities, a semi-analytical model applied to both lean single-layer flame and rich double-layer flame has been derived based on the conservation of energy in the quenching zone. In this model the flame surface radiation plays an important role. Factors influencing the radiation have been analyzed, respectively. The model indicates that the factors affecting the quenching distance in premixed flame are more complicated than that in single-wall flames or flames in tube. To fit the empirical coefficient in this model, a methane-air premixed flame quenching distance experiment under both lean and rich conditions has been performed. The comparison between the theoretical prediction and the experiment result shows that this semi-analytical model gives a suitable description of the quenching distance. The relative error of the quenching distance under different equivalence ratios and incoming flow velocities is less than ±15%.
{"title":"A Semi-Analytical Model for Prediction of Wall Quenching Distances of Premixed Flames","authors":"Huang Xia, L. Weijie","doi":"10.1115/gt2021-59809","DOIUrl":"https://doi.org/10.1115/gt2021-59809","url":null,"abstract":"\u0000 In order to predict the variation of the wall quenching distance of a premixed flame under different equivalence ratios and incoming flow velocities, a semi-analytical model applied to both lean single-layer flame and rich double-layer flame has been derived based on the conservation of energy in the quenching zone. In this model the flame surface radiation plays an important role. Factors influencing the radiation have been analyzed, respectively. The model indicates that the factors affecting the quenching distance in premixed flame are more complicated than that in single-wall flames or flames in tube. To fit the empirical coefficient in this model, a methane-air premixed flame quenching distance experiment under both lean and rich conditions has been performed. The comparison between the theoretical prediction and the experiment result shows that this semi-analytical model gives a suitable description of the quenching distance. The relative error of the quenching distance under different equivalence ratios and incoming flow velocities is less than ±15%.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129373623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ho-yin. Leung, E. Karlis, Y. Hardalupas, A. Giusti
The lean blow-out performance of an engine and the ability to re-ignite the flame, especially at high-altitude conditions, are important aspects for the safe operability of airplanes. The operability margins of the engine could be extended if it was possible to predict the occurrence of flame blowout from in-flight measurements and take actions to dynamically control the flame behaviour before complete extinction. In this work, the use of Re-currence Quantification Analysis (RQA), an established tool for the analysis of non-linear dynamical systems, is explored to reconstruct and study the blow-off dynamics starting from pressure measurements taken from blow-off experiments of an engine rig. It is shown that the dynamics of the combustor exhibit chaotic characteristics far away from blow-off and that the dynamics become more coherent as the blow-off condition is approached. The degree of determinism and recurrence rate are studied during the entire combustor’s dynamics, from stable flame to flame extinction. It is shown that the flame extinction is anticipated by an increase of the degree of determinism and recurrence rate at all investigated conditions, which indicates intermittent behavior of the combustor before the blow-off condition is reached. Therefore, in the configuration investigated here, the determinism and the recurrence rate of the system could be good predictors of blow-off occurrence and could potentially enable control actions to avoid flame extinction. This study opens up new possibilities for engine control and operability. The development of real-time RQA should be addressed in future research.
{"title":"Evaluation of Blow-Off Dynamics in Aero-Engine Combustors Using Recurrence Quantification Analysis","authors":"Ho-yin. Leung, E. Karlis, Y. Hardalupas, A. Giusti","doi":"10.1115/gt2021-59484","DOIUrl":"https://doi.org/10.1115/gt2021-59484","url":null,"abstract":"\u0000 The lean blow-out performance of an engine and the ability to re-ignite the flame, especially at high-altitude conditions, are important aspects for the safe operability of airplanes. The operability margins of the engine could be extended if it was possible to predict the occurrence of flame blowout from in-flight measurements and take actions to dynamically control the flame behaviour before complete extinction. In this work, the use of Re-currence Quantification Analysis (RQA), an established tool for the analysis of non-linear dynamical systems, is explored to reconstruct and study the blow-off dynamics starting from pressure measurements taken from blow-off experiments of an engine rig. It is shown that the dynamics of the combustor exhibit chaotic characteristics far away from blow-off and that the dynamics become more coherent as the blow-off condition is approached. The degree of determinism and recurrence rate are studied during the entire combustor’s dynamics, from stable flame to flame extinction. It is shown that the flame extinction is anticipated by an increase of the degree of determinism and recurrence rate at all investigated conditions, which indicates intermittent behavior of the combustor before the blow-off condition is reached. Therefore, in the configuration investigated here, the determinism and the recurrence rate of the system could be good predictors of blow-off occurrence and could potentially enable control actions to avoid flame extinction. This study opens up new possibilities for engine control and operability. The development of real-time RQA should be addressed in future research.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130920718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many modern low emission combustion systems suffer from thermoacoustic instabilities, which may lead to customer irritation (noise) or engine damages. The prediction of the frequency response of the flame is oftentimes not straightforward, so that it is common practice to measure the flame response in an experiment. The outcome of the measurement is typically a flame transfer-function (FTF), which can be used in low order acoustic network models to represent the flame. This paper applies an alternative criterion to evaluate the potential of the flame to become instable, the flame-amplification factor (FAF). It is based on an energy balance method and can be directly derived from the measured flame-transfer-matrix (FTM). In order to demonstrate this approach two different kerosene-driven aircraft fuel injectors were measured in the Rolls-Royce SCARLET rig in a single-sector RQL-combustor under realistic operating conditions. Here the multi-microphone method has been applied with acoustic forcing from up- and downstream side to determine the FTM. In contrast to the FTF-approach the full FTM data has been post-processed to derive the FAF. The FAF is then successfully used to rank the fuel injectors regarding their low frequency thermo-acoustic behaviour, because it is proportional to amplitudes of self-excited frequencies in FANN-rig (full annular) configuration.
{"title":"Ranking of Aircraft Fuel-Injectors Regarding Low Frequency Thermoacoustics Based on an Energy Balance Method","authors":"A. Fischer, Claus Lahiri","doi":"10.1115/gt2021-59561","DOIUrl":"https://doi.org/10.1115/gt2021-59561","url":null,"abstract":"\u0000 Many modern low emission combustion systems suffer from thermoacoustic instabilities, which may lead to customer irritation (noise) or engine damages. The prediction of the frequency response of the flame is oftentimes not straightforward, so that it is common practice to measure the flame response in an experiment. The outcome of the measurement is typically a flame transfer-function (FTF), which can be used in low order acoustic network models to represent the flame. This paper applies an alternative criterion to evaluate the potential of the flame to become instable, the flame-amplification factor (FAF). It is based on an energy balance method and can be directly derived from the measured flame-transfer-matrix (FTM). In order to demonstrate this approach two different kerosene-driven aircraft fuel injectors were measured in the Rolls-Royce SCARLET rig in a single-sector RQL-combustor under realistic operating conditions. Here the multi-microphone method has been applied with acoustic forcing from up- and downstream side to determine the FTM. In contrast to the FTF-approach the full FTM data has been post-processed to derive the FAF. The FAF is then successfully used to rank the fuel injectors regarding their low frequency thermo-acoustic behaviour, because it is proportional to amplitudes of self-excited frequencies in FANN-rig (full annular) configuration.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126165683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Antoine Durocher, Jiayi Wang, G. Bourque, J. Bergthorson
A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modelling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for non-intrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally-measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane-air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the 6 boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only provide validation targets for modelling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.
{"title":"Impact of Boundary Condition and Kinetic Parameter Uncertainties on NOx Predictions in Methane-Air Stagnation Flame Experiments","authors":"Antoine Durocher, Jiayi Wang, G. Bourque, J. Bergthorson","doi":"10.1115/gt2021-59404","DOIUrl":"https://doi.org/10.1115/gt2021-59404","url":null,"abstract":"\u0000 A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modelling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for non-intrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally-measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane-air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the 6 boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only provide validation targets for modelling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128395759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
José Ramón Quiñonez Arce, G. Andrews, A. Burns, Naman Al-Dabbagh
Grid plate flame stabilizers for low NOx emissions have renewed interest in recent years due to their use in low NOx hydrogen gas turbine combustors. For non-premixed grid plate combustion, the difference in flame stabilizer design is in how the grid plate air flow is fueled. In the present work a simple four hole grid plate is investigated using CFD with three methods of fueling the air holes: radially inward fuel injection using 8 fuel nozzles per air hole (Grid Mix, GM 1 and Micromix); central fuel injection (FLOX method); and through a fuel annulus around each air hole (GM2). ANSYS FLUENT CFD predictions for GM2 are compared with axial gas composition traverses inside the combustor and with the mean combustor exit plane emissions. The three methods of fuel injection are also compared using isothermal CFD to determine which of the three methods offer the best mixing quality, which controls the relative NOx emissions. The predictions were for an equivalence ratio of 0.624 for the combustion stage and 0.5 for the isothermal study, using industrial propane. CFD modelling used RANS simulation with Realizable k-epsilon turbulence model, non-premixed combustion with the Steady Laminar Flamelet model. The temperature and mixing profiles obtained for GM2 were in reasonable agreement with the experiments and the other two fuel injection methods were then compared with GM2.
{"title":"Grid Plate Flame Stabilizer for High Intensity Gas Turbine Combustion: The Influence of the Method of Fuel Injection on Mixing, Flame Development and NOx Emissions","authors":"José Ramón Quiñonez Arce, G. Andrews, A. Burns, Naman Al-Dabbagh","doi":"10.1115/gt2021-60105","DOIUrl":"https://doi.org/10.1115/gt2021-60105","url":null,"abstract":"\u0000 Grid plate flame stabilizers for low NOx emissions have renewed interest in recent years due to their use in low NOx hydrogen gas turbine combustors. For non-premixed grid plate combustion, the difference in flame stabilizer design is in how the grid plate air flow is fueled. In the present work a simple four hole grid plate is investigated using CFD with three methods of fueling the air holes: radially inward fuel injection using 8 fuel nozzles per air hole (Grid Mix, GM 1 and Micromix); central fuel injection (FLOX method); and through a fuel annulus around each air hole (GM2). ANSYS FLUENT CFD predictions for GM2 are compared with axial gas composition traverses inside the combustor and with the mean combustor exit plane emissions. The three methods of fuel injection are also compared using isothermal CFD to determine which of the three methods offer the best mixing quality, which controls the relative NOx emissions. The predictions were for an equivalence ratio of 0.624 for the combustion stage and 0.5 for the isothermal study, using industrial propane. CFD modelling used RANS simulation with Realizable k-epsilon turbulence model, non-premixed combustion with the Steady Laminar Flamelet model. The temperature and mixing profiles obtained for GM2 were in reasonable agreement with the experiments and the other two fuel injection methods were then compared with GM2.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128225722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ravi K., Sai Phani Keerthan Ponduri, Sriharsha Maddila
For achieving better fuel-air mixing within a short distance or for improved atomization of liquid fuels counter rotating swirler designs are preferred in gas turbine engine combustors. In this study, vortex breakdown phenomenon is investigated in co and counter rotating swirlers using CFD. The swirler assembly consists of two axial swirlers, an inner and an outer swirler both with straight vanes. Swirler vane angles are varied from 30° to 60° in steps of 10° while keeping inner and outer swirler vane angles equal. CFD simulations are performed with air at ambient conditions as the working fluid at a constant mass flow rate. It is observed that strong shear layers are created in counter swirl flows due to the opposite flow rotation. The shear layers result in rapid decay of inner swirler tangential velocities for the counter swirlers compared to the co-swirlers. The tangential velocity decay is characterized with a parameter named tangential velocity integral (TVI). TVI was observed to decay faster for the counter swirl flows compared to the co-swirl flows. The faster decay in TVI for the counter swirlers is found to result in a stronger adverse pressure gradient in the axial direction at the center. The strong adverse pressure gradient resulted in higher pressure excess ratios (PER) for the counter swirlers. The higher PERs are observed to induce vortex breakdown in counter swirlers even at low vane angles whereas in co-swirlers vortex breakdown is not observed except for the highest vane angle. It is demonstrated that vortex breakdown could be suppressed in counter swirlers using a converging mixer passage. The converging mixer passage creates a favorable pressure gradient that counters the adverse pressure gradient due to swirl decay, resulting in breakdown suppression.
{"title":"Vortex Breakdown and Recirculation Bubble Formation in Counter Swirl Flows","authors":"Ravi K., Sai Phani Keerthan Ponduri, Sriharsha Maddila","doi":"10.1115/gt2021-60005","DOIUrl":"https://doi.org/10.1115/gt2021-60005","url":null,"abstract":"\u0000 For achieving better fuel-air mixing within a short distance or for improved atomization of liquid fuels counter rotating swirler designs are preferred in gas turbine engine combustors. In this study, vortex breakdown phenomenon is investigated in co and counter rotating swirlers using CFD. The swirler assembly consists of two axial swirlers, an inner and an outer swirler both with straight vanes. Swirler vane angles are varied from 30° to 60° in steps of 10° while keeping inner and outer swirler vane angles equal. CFD simulations are performed with air at ambient conditions as the working fluid at a constant mass flow rate. It is observed that strong shear layers are created in counter swirl flows due to the opposite flow rotation. The shear layers result in rapid decay of inner swirler tangential velocities for the counter swirlers compared to the co-swirlers. The tangential velocity decay is characterized with a parameter named tangential velocity integral (TVI). TVI was observed to decay faster for the counter swirl flows compared to the co-swirl flows. The faster decay in TVI for the counter swirlers is found to result in a stronger adverse pressure gradient in the axial direction at the center. The strong adverse pressure gradient resulted in higher pressure excess ratios (PER) for the counter swirlers. The higher PERs are observed to induce vortex breakdown in counter swirlers even at low vane angles whereas in co-swirlers vortex breakdown is not observed except for the highest vane angle. It is demonstrated that vortex breakdown could be suppressed in counter swirlers using a converging mixer passage. The converging mixer passage creates a favorable pressure gradient that counters the adverse pressure gradient due to swirl decay, resulting in breakdown suppression.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"294 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127417361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ghazanfar Mehdi, M. D. Giorgi, D. Fontanarosa, S. Bonuso, A. Ficarella
This study focused on the comparative analysis about the production of ozone and active radicals in presence of nanopulsed plasma discharge on air and on fuel/air mixture to investigate its effect on combustion enhancement. This analysis is based on numerical modeling of air and methane/air plasma discharge with different repetition rates (100 Hz, 1000 Hz and 10000 Hz). To this purpose, a two-step approach has been proposed based on two different chemistry solvers: a 0-D plasma chemistry solver (ZDPlasKin toolbox) and a combustion chemistry solver (CHEMKIN software suite). Consequently, a comprehensive chemical kinetic scheme was generated including both plasma excitation reactions and gas phase reactions. Validation of air and methane/air mechanisms was performed with experimental data. Kinetic models of both air and methane/air provides good fitting with experimental data of O atom generation and decay process. ZDPlasKin results were introduced in CHEMKIN in order to analyze combustion enhancement. It was found that the concentrations of O3 and O atom in air are higher than the methane/air activation. However, during the air activation peak concentration of ozone was significantly increased with repetition rates and maximum was observed at 10000 Hz. Furthermore, ignition timings and flammability limits were also improved with air and methane/air activation but the impact of methane/air activation was comparatively higher.
{"title":"Ozone Production With Plasma Discharge: Comparisons Between Activated Air and Activated Fuel/Air Mixture","authors":"Ghazanfar Mehdi, M. D. Giorgi, D. Fontanarosa, S. Bonuso, A. Ficarella","doi":"10.1115/gt2021-60167","DOIUrl":"https://doi.org/10.1115/gt2021-60167","url":null,"abstract":"\u0000 This study focused on the comparative analysis about the production of ozone and active radicals in presence of nanopulsed plasma discharge on air and on fuel/air mixture to investigate its effect on combustion enhancement. This analysis is based on numerical modeling of air and methane/air plasma discharge with different repetition rates (100 Hz, 1000 Hz and 10000 Hz). To this purpose, a two-step approach has been proposed based on two different chemistry solvers: a 0-D plasma chemistry solver (ZDPlasKin toolbox) and a combustion chemistry solver (CHEMKIN software suite). Consequently, a comprehensive chemical kinetic scheme was generated including both plasma excitation reactions and gas phase reactions. Validation of air and methane/air mechanisms was performed with experimental data. Kinetic models of both air and methane/air provides good fitting with experimental data of O atom generation and decay process. ZDPlasKin results were introduced in CHEMKIN in order to analyze combustion enhancement. It was found that the concentrations of O3 and O atom in air are higher than the methane/air activation. However, during the air activation peak concentration of ozone was significantly increased with repetition rates and maximum was observed at 10000 Hz. Furthermore, ignition timings and flammability limits were also improved with air and methane/air activation but the impact of methane/air activation was comparatively higher.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122265115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Combustion dynamics has been a significant problem for a lean, premixed, prevaporized (LPP) combustor. Understanding the acoustic characteristics of combustor components is essential to modeling thermoacoustic behavior in a gas turbine combustion system. Acoustic characteristics such as impedance and scattering matrix elements are experimentally determined for different-shape orifices with an emphasis on the effect of the flow field on them. These orifices are used to represent premixed swirl cups in LP combustors. The validity and limitation of two different methodologies are evaluated by comparing measured results with those of others. Consistent with analytical predictions, the measured resistance through an orifice increases as the bias flow increases. Different types of orifices considered in this study behave similarly to a thin orifice at high bias flow even though the discharge coefficients vary as much as 30% between them. The conventional method produces impedance values independent of waves reflected from the end boundary condition only when the scattering elements at the orifice downstream are roughly equal to those upstream of the orifice. However, the scattering matrix method produces impedance values that are not affected by the source or reflected waves at the system’s boundary. The scattering matrix measurements show that the reflection and transmission elements increases and decreases, respectively, as the bias flow through an orifice increases.
{"title":"Experimental Investigation of Acoustic Characteristic on Orifice Shaped With Bias Flow","authors":"Melvin Ikwubuo, Jinkwan Song, J. Lee","doi":"10.1115/gt2021-60118","DOIUrl":"https://doi.org/10.1115/gt2021-60118","url":null,"abstract":"\u0000 Combustion dynamics has been a significant problem for a lean, premixed, prevaporized (LPP) combustor. Understanding the acoustic characteristics of combustor components is essential to modeling thermoacoustic behavior in a gas turbine combustion system. Acoustic characteristics such as impedance and scattering matrix elements are experimentally determined for different-shape orifices with an emphasis on the effect of the flow field on them. These orifices are used to represent premixed swirl cups in LP combustors. The validity and limitation of two different methodologies are evaluated by comparing measured results with those of others. Consistent with analytical predictions, the measured resistance through an orifice increases as the bias flow increases. Different types of orifices considered in this study behave similarly to a thin orifice at high bias flow even though the discharge coefficients vary as much as 30% between them. The conventional method produces impedance values independent of waves reflected from the end boundary condition only when the scattering elements at the orifice downstream are roughly equal to those upstream of the orifice. However, the scattering matrix method produces impedance values that are not affected by the source or reflected waves at the system’s boundary. The scattering matrix measurements show that the reflection and transmission elements increases and decreases, respectively, as the bias flow through an orifice increases.","PeriodicalId":395231,"journal":{"name":"Volume 3B: Combustion, Fuels, and Emissions","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129516070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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