The turbulent combustion flow modeling is performed to study the effects of CO_2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approa...The turbulent combustion flow modeling is performed to study the effects of CO_2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approach along with three well-known turbulence models is utilized to model the turbulent combustion flow field. The k-ω shear stress transport(SST) model shows the best agreement with the experimental measurements compared with other models. Therefore, the k-ω SST model is used to study the effects of CO_2 dilution on the flame structure and strength, temperature distribution, and CO concentration. To determine the chemical effects of CO_2 dilution, a fictitious species is replaced with the regular CO_2 in both the fuel stream and the oxidizer stream. The results indicate that the flame temperature decreases when CO_2 is added to either the fuel or the oxidizer stream. The flame length reduction is observed at all levels of CO_2 dilution. The H radical concentration indicating the flame strength decreases, following by the thermochemical effects of CO_2 dilution processes. In comparison with the fictitious species dilution, the chemical effects of CO_2 addition enhance the CO mass fraction. The numerical simulations show that when the dilution level is higher, the rate of the flame length reduction is more significant at low swirl numbers.展开更多
Molecular mechanics-based finite element(FE)models of graphene sheet and singlewalled zigzag and armchair carbon nanotubes(CNTs)are developed on the basis of the assumption that the carbon nanostructures,when loaded,b...Molecular mechanics-based finite element(FE)models of graphene sheet and singlewalled zigzag and armchair carbon nanotubes(CNTs)are developed on the basis of the assumption that the carbon nanostructures,when loaded,behave like frame structures.The behavior of carbon–carbon bonds,which are represented by beam elements,is simulated using the many-body second generation reactive empirical bond order(REBO)potential.By means of the FE models,the tensile behavior of carbon nanostructures is simulated.The FE models are verified against molecular dynamics simulations.The computed results in terms of tensile stress–strain curves and fracture patterns are compared with results obtained using the pairwise modified-Morse potential.Different tensile properties and fracture patterns are predicted using the two potentials.This is mainly attributed to the deviations in the force–bond length curves and to the contribution of bond angle variation which is present in REBO.The present work is the first attempt to implement the REBO potential into a continuum model of carbon nanostructures and paves the way for a more systematic incorporation of atomistic simulation methods into continuum models.展开更多
文摘The turbulent combustion flow modeling is performed to study the effects of CO_2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approach along with three well-known turbulence models is utilized to model the turbulent combustion flow field. The k-ω shear stress transport(SST) model shows the best agreement with the experimental measurements compared with other models. Therefore, the k-ω SST model is used to study the effects of CO_2 dilution on the flame structure and strength, temperature distribution, and CO concentration. To determine the chemical effects of CO_2 dilution, a fictitious species is replaced with the regular CO_2 in both the fuel stream and the oxidizer stream. The results indicate that the flame temperature decreases when CO_2 is added to either the fuel or the oxidizer stream. The flame length reduction is observed at all levels of CO_2 dilution. The H radical concentration indicating the flame strength decreases, following by the thermochemical effects of CO_2 dilution processes. In comparison with the fictitious species dilution, the chemical effects of CO_2 addition enhance the CO mass fraction. The numerical simulations show that when the dilution level is higher, the rate of the flame length reduction is more significant at low swirl numbers.
文摘Molecular mechanics-based finite element(FE)models of graphene sheet and singlewalled zigzag and armchair carbon nanotubes(CNTs)are developed on the basis of the assumption that the carbon nanostructures,when loaded,behave like frame structures.The behavior of carbon–carbon bonds,which are represented by beam elements,is simulated using the many-body second generation reactive empirical bond order(REBO)potential.By means of the FE models,the tensile behavior of carbon nanostructures is simulated.The FE models are verified against molecular dynamics simulations.The computed results in terms of tensile stress–strain curves and fracture patterns are compared with results obtained using the pairwise modified-Morse potential.Different tensile properties and fracture patterns are predicted using the two potentials.This is mainly attributed to the deviations in the force–bond length curves and to the contribution of bond angle variation which is present in REBO.The present work is the first attempt to implement the REBO potential into a continuum model of carbon nanostructures and paves the way for a more systematic incorporation of atomistic simulation methods into continuum models.
