4pi Models of CMEs and ICMEs

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major anifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-bound missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3-D ('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication in Solar Physics (SUN-360 topical issue

Large-Eddy Simulation of lean hydrogen-methane turbulent premixed flames in the methane-dominated regime

The application of large-eddy simulation (LES) to the prediction of H2-enriched lean methane–air turbulent premixed combustion is considered. A presumed conditional moment (PCM) subfilter-scale combustion model is coupled with the flame prolongation of intrinsic low-dimensional manifold (FPI) chemistry tabulation technique. The LES and PCM-FPI modelling procedures are then applied to the prediction of laboratory-scale axisymmetric Bunsen-type turbulent premixed flames. Both premixed methane–air and H2-enriched methane–air flames are considered and the predicted solutions are examined and compared to available experimental data. The enriched flame has 20% H2 in terms of mole fraction and lies in the methane-dominated regime of hydrogen–methane mixtures. The LES simulations predict similar qualitative trends to those found in the experiments for flame height and curvature. The addition of H2 decreases the flame height and broadens the curvature probability density functions, which show a Gaussian-type shape centred around zero. Moreover, the enriched flame displays a higher degree of wrinkling with sharper ridges of negative curvature and larger pockets of positive curvature. Overall, the proposed treatment for the PCM-FPI combustion model, in terms of progress variable and tabulated data, seems to perform well for the H2-enriched methane flame in the methane-dominated regime

Large-Eddy Simulation of lean hydrogen-methane turbulent premixed flames in the methane-dominated regime

The application of large-eddy simulation (LES) to the prediction of H2-enriched lean methane–air turbulent premixed combustion is considered. A presumed conditional moment (PCM) subfilter-scale combustion model is coupled with the flame prolongation of intrinsic low-dimensional manifold (FPI) chemistry tabulation technique. The LES and PCM-FPI modelling procedures are then applied to the prediction of laboratory-scale axisymmetric Bunsen-type turbulent premixed flames. Both premixed methane–air and H2-enriched methane–air flames are considered and the predicted solutions are examined and compared to available experimental data. The enriched flame has 20% H2 in terms of mole fraction and lies in the methane-dominated regime of hydrogen–methane mixtures. The LES simulations predict similar qualitative trends to those found in the experiments for flame height and curvature. The addition of H2 decreases the flame height and broadens the curvature probability density functions, which show a Gaussian-type shape centred around zero. Moreover, the enriched flame displays a higher degree of wrinkling with sharper ridges of negative curvature and larger pockets of positive curvature. Overall, the proposed treatment for the PCM-FPI combustion model, in terms of progress variable and tabulated data, seems to perform well for the H2-enriched methane flame in the methane-dominated regime

LES of a laboratory-scale turbulent premixed bunsen flame using FSD, PCM-FPI and thickened flame models

Large-eddy simulations (LES) of a turbulent premixed Bunsen flame were carried out with three subfilter-scale (SFS) modelling approaches for turbulent premixed combustion. One approach is based on the artificially thickened flame and power-law flame wrinkling models, the second approach is based on the presumed conditional moment (PCM) with flame prolongation of intrinsic low-dimensional manifolds (FPI) tabulated chemistry, and the third approach is based on a transport equation for the flame surface density (FSD). A lean methane–air flame at equivalence ratio ¿=0.7, which was studied experimentally by Yuen and Gülder, was considered. The predicted LES solutions were compared to the experimental data. The resolved instantaneous three-dimensional structure of the predicted flames compares well with that of the experiment. Flame heights and resolvable flame surface density and curvature were also examined. In general, the average flame height was well predicted. Furthermore, the flame surface data extracted from the simulations showed remarkably good qualitative agreement with the experimental results. The probability density functions of predicted flame curvature displayed a Gaussian-like shape centred around zero as also observed in the experimental flame, although the experimental data showed a slightly wider profile. The results of the comparisons highlight the weaknesses and the strengths of SFS modelling approaches commonly used in LES of turbulent premixed flame