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Gang Zhao - One of the best experts on this subject based on the ideXlab platform.
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statistical equilibrium of silicon in the solar atmosphere
Astronomy and Astrophysics, 2008Co-Authors: Jianrong Shi, T Gehren, K Butler, L Mashonkina, Gang ZhaoAbstract:Aims. The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated. Line formation is discussed and the solar silicon abundance determined. Methods. High-resolution solar spectra were used to determine solar log g f eSi values by comparison with Si line synthesis based on LTE and NLTE level populations. The results will be used in a forthcoming paper for differential abundance analyses of metalpoor stars. A detailed analysis of silicon line spectra leads to setting up realistic model atoms, which are exposed to Interactions in plane-parallel solar atmospheric models. The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum. Results. The statistical equilibrium of Si i turns out to depend marginally on bound-Free Interaction processes, both radiative and collisional. Bound-bound Interaction processes do not play a significant role either, except for hydrogen collisions, which have to be chosen adequately for fitting the cores of the near-infrared lines. Except for some near-infrared lines, the NLTE influence on the abundances is weak. Conclusions. Taking the deviations from LTE in silicon into account, it is possible to calculate the ionisation equilibrium from neutral and ionised lines. The solar abundance based on the experimental f -values of Garz corrected for the Becker et al.’s measurement is 7.52 ± 0.05. Combined with an extended line sample with selected NIST f -values, the solar abundance is 7.52 ± 0.06, with a nearly perfect ionisation equilibrium of Δ log e� (Siii/Sii) = −0.01.
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statistical equilibrium of silicon in the solar atmosphere
arXiv: Astrophysics, 2008Co-Authors: Jianrong Shi, T Gehren, K Butler, L Mashonkina, Gang ZhaoAbstract:The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated. Line formation is discussed and the solar silicon abundance determined. High-resolution solar spectra were used to determine solar $\log gf\epsilon_{\rm Si}$ values by comparison with Si line synthesis based on LTE and NLTE level populations. The results will be used in a forthcoming paper for differential abundance analyses of metal-poor stars. A detailed analysis of silicon line spectra leads to setting up realistic model atoms, which are exposed to Interactions in plane-parallel solar atmospheric models. The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum. The statistical equilibrium of \ion{Si}{i} turns out to depend marginally on bound-Free Interaction processes, both radiative and collisional. Bound-bound Interaction processes do not play a significant role either, except for hydrogen collisions, which have to be chosen adequately for fitting the cores of the near-infrared lines. Except for some near-infrared lines, the NLTE influence on the abundances is weak. Taking the deviations from LTE in silicon into account, it is possible to calculate the ionisation equilibrium from neutral and ionised lines. The solar abundance based on the experimental $f$-values of Garz corrected for the Becker et al.'s measurement is $7.52 \pm 0.05$. Combined with an extended line sample with selected NIST $f$-values, the solar abundance is $7.52 \pm 0.06$, with a nearly perfect ionisation equilibrium of $\Delta\log\epsilon_\odot(\ion{Si}{ii}/\ion{Si}{i}) = -0.01$.
Stefan Hickel - One of the best experts on this subject based on the ideXlab platform.
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on the transition between regular and irregular shock patterns of shock wave boundary layer Interactions
Journal of Fluid Mechanics, 2015Co-Authors: Jan Matheis, Stefan HickelAbstract:The reflection of strong oblique shock waves at turbulent boundary layers is studied numerically and analytically. A particular emphasis is put on the transition between regular shock-wave/boundary-layer Interaction (SWBLI) and Mach reflection (irregular SWBLI). The classical two- and three-shock theory and a generalised form of the Free Interaction theory are used for the analysis of well-resolved large-eddy simulations (LES) and for the derivation of stability criteria. We found that at a critical deflection angle across the incident shock wave, the perturbations related to the turbulent boundary layer cause bi-directional transition processes between regular and irregular shock patterns for a Free-stream Mach number of . Computational results show that the mean deflection angle across the separation shock is decoupled from the incident shock wave and can be accurately modelled by the generalised Free Interaction theory. On the basis of these observations, and the von Neumann and detachment criteria for the asymmetric intersection of shock waves, we derive the critical incident shock deflection angles at which the shock pattern may/must become irregular. Numerical data for a Free-stream Mach number of confirm the existence of the dual-solution domain predicted by theory.
Jianrong Shi - One of the best experts on this subject based on the ideXlab platform.
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statistical equilibrium of silicon in the solar atmosphere
Astronomy and Astrophysics, 2008Co-Authors: Jianrong Shi, T Gehren, K Butler, L Mashonkina, Gang ZhaoAbstract:Aims. The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated. Line formation is discussed and the solar silicon abundance determined. Methods. High-resolution solar spectra were used to determine solar log g f eSi values by comparison with Si line synthesis based on LTE and NLTE level populations. The results will be used in a forthcoming paper for differential abundance analyses of metalpoor stars. A detailed analysis of silicon line spectra leads to setting up realistic model atoms, which are exposed to Interactions in plane-parallel solar atmospheric models. The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum. Results. The statistical equilibrium of Si i turns out to depend marginally on bound-Free Interaction processes, both radiative and collisional. Bound-bound Interaction processes do not play a significant role either, except for hydrogen collisions, which have to be chosen adequately for fitting the cores of the near-infrared lines. Except for some near-infrared lines, the NLTE influence on the abundances is weak. Conclusions. Taking the deviations from LTE in silicon into account, it is possible to calculate the ionisation equilibrium from neutral and ionised lines. The solar abundance based on the experimental f -values of Garz corrected for the Becker et al.’s measurement is 7.52 ± 0.05. Combined with an extended line sample with selected NIST f -values, the solar abundance is 7.52 ± 0.06, with a nearly perfect ionisation equilibrium of Δ log e� (Siii/Sii) = −0.01.
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statistical equilibrium of silicon in the solar atmosphere
arXiv: Astrophysics, 2008Co-Authors: Jianrong Shi, T Gehren, K Butler, L Mashonkina, Gang ZhaoAbstract:The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated. Line formation is discussed and the solar silicon abundance determined. High-resolution solar spectra were used to determine solar $\log gf\epsilon_{\rm Si}$ values by comparison with Si line synthesis based on LTE and NLTE level populations. The results will be used in a forthcoming paper for differential abundance analyses of metal-poor stars. A detailed analysis of silicon line spectra leads to setting up realistic model atoms, which are exposed to Interactions in plane-parallel solar atmospheric models. The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum. The statistical equilibrium of \ion{Si}{i} turns out to depend marginally on bound-Free Interaction processes, both radiative and collisional. Bound-bound Interaction processes do not play a significant role either, except for hydrogen collisions, which have to be chosen adequately for fitting the cores of the near-infrared lines. Except for some near-infrared lines, the NLTE influence on the abundances is weak. Taking the deviations from LTE in silicon into account, it is possible to calculate the ionisation equilibrium from neutral and ionised lines. The solar abundance based on the experimental $f$-values of Garz corrected for the Becker et al.'s measurement is $7.52 \pm 0.05$. Combined with an extended line sample with selected NIST $f$-values, the solar abundance is $7.52 \pm 0.06$, with a nearly perfect ionisation equilibrium of $\Delta\log\epsilon_\odot(\ion{Si}{ii}/\ion{Si}{i}) = -0.01$.
Bas Van Oudheusden - One of the best experts on this subject based on the ideXlab platform.
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theoretical study on regular reflection of shock wave boundary layer Interactions
Journal of Fluid Mechanics, 2020Co-Authors: Longsheng Xue, F F J Schrijer, Bas Van Oudheusden, Chengpeng Wang, Zhiwei Shi, Keming ChengAbstract:In this paper the configurations of shock wave–boundary layer Interactions (SWBLI) are studied theoretically and experimentally in Mach number 2 and 2.5 flows on test models with various wedge angles ranging from $9^\circ$ to $21^\circ$ . The proposed theoretical method couples the Free Interaction theory (FIT) with the minimum entropy production (MEP) principle to predict the appearance of separation shock, resulting in convex, straight and concave separation shock waves according to different solution combinations, which agree well with current experiments. Additionally, several influences on SWBLI are studied experimentally, in which the parameters related to theoretical solutions are found mostly determining the flow configuration, and SWBLI is much more sensitive to incident shock strength than incoming flow properties. Separation could be suppressed by incident shock when the MEP solution is smaller than the FIT, while it could be intensified when the MEP solution is larger than FIT; by contrast, the effects of separation position and model mounting height could be very weak.
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a parametric study of laminar and transitional oblique shock wave reflections
Journal of Fluid Mechanics, 2018Co-Authors: Rogier Giepman, F F J Schrijer, Bas Van OudheusdenAbstract:High-resolution particle image velocimetry measurements were performed on laminar and transitional oblique shock wave reflections for a range of Mach numbers (M D 1:6-2:3), Reynolds numbers (Re xsh D 1.4×10 6 -3.5×10 6 ) and flow deflection angles (θ 1°-5° or p3=p1 D 1.11-1.64). The laminar Interactions revealed a long, flat and triangular shaped separation bubble. For relatively strong Interactions (p3=p1 g 1.2), the bubble grows linearly in the upstream direction with increasing shock strength. Under these conditions, the boundary layer keeps an on average laminar velocity profile up to the shock impingement location, followed by a quick transition and subsequent reattachment of the boundary layer. For weaker Interactions (p3=p1 l 1.2), the boundary layer is able to remain laminar further downstream of the bubble, which consequently results in a later reattachment of the boundary layer. The pressure distribution at the Interaction onset for all laminar cases shows excellent agreement with the Free-Interaction theory, therefore supporting its validity even for incipiently separated laminar oblique shock wave reflections.
Paul J K Bruce - One of the best experts on this subject based on the ideXlab platform.
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confinement effects on regular irregular transition in shock wave boundary layer Interactions
Journal of Fluid Mechanics, 2018Co-Authors: Ilan J Grossman, Paul J K BruceAbstract:An oblique shock wave is generated in a Mach 2 flow at a flow deflection angle of $12^{\circ }$ . The resulting shock-wave–boundary-layer Interaction (SWBLI) at the tunnel wall is observed. A novel traversable shock generator allows the position of the SWBLI to be varied relative to a downstream expansion fan. The relationship between the SWBLI, the expansion fan and the wind tunnel arrangement is studied. Schlieren photography, surface oil flow visualisation, particle image velocimetry and high-spatial-resolution wall pressure measurements are used to investigate the flow. It is observed that stream-normal movement of the shock generator downwards (towards the floor and hence the point of shock reflection) is accompanied by (1) growth in the streamwise extent of the shock-induced boundary layer separation, (2) upstream movement of the shock-induced separation point while the reattachment point remains nearly fixed, (3) an increase in separation shock strength and (4) transition between regular and irregular (Mach) reflection without an increase in incident shock strength. The role of Free Interaction theory in defining the separation shock angle is considered and shown to be consistent with the present measurements over a short streamwise extent. An SWBLI representation is proposed and reasoned which explains the apparent increase in separation shock strength that occurs without an increase in incident shock strength.
