Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemis...Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function （PDF）. A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function （Model I） and //-function （Model II）, are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement （AMR） technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.展开更多
A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structu...A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structures, two self-contained flame sensors are used to track the diffusion and reaction processes with different spatial scales in the flame front, respectively. The dynamic formulation for the proposed SGS combustion model is also performed. Large eddy simulations(LESs) of Bunsen flame F3 are used to evaluate the different SGS combustion models. The results show that the proposed SGS model has the ability in predicting the distributions of temperature and velocity reasonably, while the predictions for the distributions of some species need further improvement. The snapshots of instantaneous normalized progress variables reveal that the flame is more remarkably and severely wrinkled at the flame tip for flame F3.More satisfactory results obtained by the dynamic model indicate that it can preserve the premixed flame propagation characteristics better.展开更多
Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling facto...Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence.The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.展开更多
The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan （JCY） triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representi...The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan （JCY） triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representing various shallow-water platform environments. Highly diversified and abundant heliolitid coral faunas are recognized in the formation and occur over time and space in certain stratigraphic horizons and various lithofacies. Heliolites has been studied using multivariate morphometric analysis applied to differentiate species and evaluate intraspecific and interspecific variations. Ten morphological characters quantified by examination and measurement from transverse and longitudinal thin sections and statistically tested allowed selection of effective characters to discriminate species. Results of frequency histograms, correlation analysis and principle component analysis indicated that certain characters would be suitable for cluster analysis, which were performed on principle component score matrices obtained from the raw data set coordinated with coralla by all those characters. Five major clusters at a relative distance of five on the resulting dendrogram of Heliolites are regarded as morphospecies thus making valid taxa： Heliolites tashanensis Lin and Chow, 1977; Heliolites caracolica （Lin and Chow, 1977）; Heliolites columella （Lin and Chow, 1977）; Heliolites waicunensis Lin and Chow, 1977; and H. sinensis irregularis Lin and Chow, 1977. The discrimination of these morphospecies by the cluster analysis is verified by discriminant analyses and descriptive statistics.展开更多
基金financial support by the National Natural Science Foundation of China (Nos. 51176178, 50936005)
文摘Large eddy simulations （LES） have been performed to investigate the flow and combustion fields in the scramjet of the German Aerospace Center （DLR）. Turbulent combustion is mod- eled by the tabulated thermo-chemistry approach in combination with the presumed probability density function （PDF）. A/3-function is used to model the distribution of the mixture fraction, while two different PDFs, g-function （Model I） and //-function （Model II）, are applied to model the reaction progress. Temperature is obtained by solving filtered energy transport equation and the reaction rate of the progress variable is rescaled by pressure to consider the effects of compressibil- ity. The adaptive mesh refinement （AMR） technique is used to properly capture shock waves, boundary layers, shear layers and flame structures. Statistical results of temperature and velocity predicted by Model II show better accuracy than that predicted by Model I. The results of scatter points and mixture fraction-conditional variables indicate the significant differences between Model I and Model II. It is concluded that second moment information in the presumed PDF of the reaction progress is very important in the simulation of supersonic combustion. It is also found that an unstable flame with extinction and ignition develops in the shear layers of bluff body and a fuel- rich partially premixed flame stabilizes in the central recirculation bubble.
基金Project supported by the National Natural Science Foundation of China(Nos.91441117 and 51576182)
文摘A sub-grid scale(SGS) combustion model, which combines the artificial thickened flame(ATF) model with the flamelet generated manifold(FGM) tabulation method, is proposed. Based on the analysis of laminar flame structures, two self-contained flame sensors are used to track the diffusion and reaction processes with different spatial scales in the flame front, respectively. The dynamic formulation for the proposed SGS combustion model is also performed. Large eddy simulations(LESs) of Bunsen flame F3 are used to evaluate the different SGS combustion models. The results show that the proposed SGS model has the ability in predicting the distributions of temperature and velocity reasonably, while the predictions for the distributions of some species need further improvement. The snapshots of instantaneous normalized progress variables reveal that the flame is more remarkably and severely wrinkled at the flame tip for flame F3.More satisfactory results obtained by the dynamic model indicate that it can preserve the premixed flame propagation characteristics better.
基金Project supported by the National Natural Science Foundation of China(Nos.91441117 and51576182)
文摘Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the turbulence.The combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.
基金supported by grants to Prof.Dong-Jin Lee from the Korean Research Foundation
文摘The Upper Ordovician Xiazhen Formation in the Jiangshan-Changshan-Yushan （JCY） triangle area on the Zhejiang-Jiangxi provincial border, South China, is composed of a mixed carbonate-siliciclastic sequence representing various shallow-water platform environments. Highly diversified and abundant heliolitid coral faunas are recognized in the formation and occur over time and space in certain stratigraphic horizons and various lithofacies. Heliolites has been studied using multivariate morphometric analysis applied to differentiate species and evaluate intraspecific and interspecific variations. Ten morphological characters quantified by examination and measurement from transverse and longitudinal thin sections and statistically tested allowed selection of effective characters to discriminate species. Results of frequency histograms, correlation analysis and principle component analysis indicated that certain characters would be suitable for cluster analysis, which were performed on principle component score matrices obtained from the raw data set coordinated with coralla by all those characters. Five major clusters at a relative distance of five on the resulting dendrogram of Heliolites are regarded as morphospecies thus making valid taxa： Heliolites tashanensis Lin and Chow, 1977; Heliolites caracolica （Lin and Chow, 1977）; Heliolites columella （Lin and Chow, 1977）; Heliolites waicunensis Lin and Chow, 1977; and H. sinensis irregularis Lin and Chow, 1977. The discrimination of these morphospecies by the cluster analysis is verified by discriminant analyses and descriptive statistics.
