The Experts below are selected from a list of 206115 Experts worldwide ranked by ideXlab platform
Andrea Verdini - One of the best experts on this subject based on the ideXlab platform.
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imprints of expansion on the local anisotropy of solar wind turbulence
The Astrophysical Journal, 2015Co-Authors: Andrea Verdini, Roland GrappinAbstract:We study the anisotropy of II-order structure functions (SFs) defined in a frame attached to the local mean field in three-dimensional (3D) direct Numerical simulations of magnetohydrodynamic turbulence, with the solar wind expansion both included and not included. We simulate spacecraft flybys through the Numerical Domain by taking increments along the radial (wind) direction that form an angle of 45° with the ambient magnetic field. We find that only when expansion is taken into account do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scale. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order SF by influencing the distribution of the local mean field, which enters this higher-order statistics.
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imprints of expansion onto the local anisotropy of solar wind turbulence
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Andrea Verdini, Roland GrappinAbstract:We study the anisotropy of II-order structure functions defined in a frame attached to the local mean field in three-dimensional (3D) direct Numerical simulations of magnetohydrodynamic turbulence, including or not the solar wind expansion. We simulate spacecraft flybys through the Numerical Domain by taking increments along the radial (wind) direction that forms an angle of $45^o$ with the ambient magnetic field. We find that only when expansion is taken into account, do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scales. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order structure functions by influencing the distribution of the local mean field, which enters this higher-order statistics.
Roland Grappin - One of the best experts on this subject based on the ideXlab platform.
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imprints of expansion on the local anisotropy of solar wind turbulence
The Astrophysical Journal, 2015Co-Authors: Andrea Verdini, Roland GrappinAbstract:We study the anisotropy of II-order structure functions (SFs) defined in a frame attached to the local mean field in three-dimensional (3D) direct Numerical simulations of magnetohydrodynamic turbulence, with the solar wind expansion both included and not included. We simulate spacecraft flybys through the Numerical Domain by taking increments along the radial (wind) direction that form an angle of 45° with the ambient magnetic field. We find that only when expansion is taken into account do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scale. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order SF by influencing the distribution of the local mean field, which enters this higher-order statistics.
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imprints of expansion onto the local anisotropy of solar wind turbulence
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Andrea Verdini, Roland GrappinAbstract:We study the anisotropy of II-order structure functions defined in a frame attached to the local mean field in three-dimensional (3D) direct Numerical simulations of magnetohydrodynamic turbulence, including or not the solar wind expansion. We simulate spacecraft flybys through the Numerical Domain by taking increments along the radial (wind) direction that forms an angle of $45^o$ with the ambient magnetic field. We find that only when expansion is taken into account, do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scales. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order structure functions by influencing the distribution of the local mean field, which enters this higher-order statistics.
Martin Schnieder - One of the best experts on this subject based on the ideXlab platform.
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validation and analysis of Numerical results for a varying aspect ratio two pass internal cooling channel
Journal of Heat Transfer-transactions of The Asme, 2011Co-Authors: Igor V Shevchuk, Bernhard Weigand, Sean C Jenkins, Jens Von Wolfersdorf, Sven Olaf Neumann, Martin SchniederAbstract:Numerical results for an internal ribbed cooling channel including a 180 deg bend with a 2:1 inlet and a 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The Numerical Domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet chcannel to reduce the overall Numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions, and the Numerical results captured the predominate flow physics resulting from the 180 deg bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance, while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance, while pressure losses followed a nonlinear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.
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validation and analysis of Numerical results for a varying aspect ratio two pass internal cooling channel
ASME Turbo Expo 2008: Power for Land Sea and Air, 2008Co-Authors: Igor V Shevchuk, Bernhard Weigand, Sean C Jenkins, Jens Von Wolfersdorf, Sven Olaf Neumann, Martin SchniederAbstract:Numerical results for an internal ribbed cooling channel including a 180° bend with a 2:1 inlet and 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The Numerical Domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet channel to reduce the overall Numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions and the Numerical results captured the predominate flow physics resulting from the 180° bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance while pressure losses followed a non-linear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.Copyright © 2008 by Alstom
Ahmed F Ghoniem - One of the best experts on this subject based on the ideXlab platform.
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a second order coupled immersed boundary samr construction for chemically reacting flow over a heat conducting cartesian grid conforming solid
Journal of Computational Physics, 2014Co-Authors: Kushal S Kedia, Cosmin Safta, Habib N. Najm, Ahmed F GhoniemAbstract:Abstract In this paper, we present a second-order Numerical method for simulations of reacting flow around heat-conducting immersed solid objects. The method is coupled with a block-structured adaptive mesh refinement (SAMR) framework and a low-Mach number operator-split projection algorithm. A “buffer zone” methodology is introduced to impose the solid–fluid boundary conditions such that the solver uses symmetric derivatives and interpolation stencils throughout the interior of the Numerical Domain; irrespective of whether it describes fluid or solid cells. Solid cells are tracked using a binary marker function. The no-slip velocity boundary condition at the immersed wall is imposed using the staggered mesh. Near the immersed solid boundary, single-sided buffer zones (inside the solid) are created to resolve the species discontinuities, and dual buffer zones (inside and outside the solid) are created to capture the temperature gradient discontinuities. The development discussed in this paper is limited to a two-dimensional Cartesian grid-conforming solid. We validate the code using benchmark simulations documented in the literature. We also demonstrate the overall second-order convergence of our Numerical method. To demonstrate its capability, a reacting flow simulation of a methane/air premixed flame stabilized on a channel-confined bluff-body using a detailed chemical kinetics model is discussed.
Igor V Shevchuk - One of the best experts on this subject based on the ideXlab platform.
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validation and analysis of Numerical results for a varying aspect ratio two pass internal cooling channel
Journal of Heat Transfer-transactions of The Asme, 2011Co-Authors: Igor V Shevchuk, Bernhard Weigand, Sean C Jenkins, Jens Von Wolfersdorf, Sven Olaf Neumann, Martin SchniederAbstract:Numerical results for an internal ribbed cooling channel including a 180 deg bend with a 2:1 inlet and a 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The Numerical Domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet chcannel to reduce the overall Numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions, and the Numerical results captured the predominate flow physics resulting from the 180 deg bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance, while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance, while pressure losses followed a nonlinear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.
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validation and analysis of Numerical results for a varying aspect ratio two pass internal cooling channel
ASME Turbo Expo 2008: Power for Land Sea and Air, 2008Co-Authors: Igor V Shevchuk, Bernhard Weigand, Sean C Jenkins, Jens Von Wolfersdorf, Sven Olaf Neumann, Martin SchniederAbstract:Numerical results for an internal ribbed cooling channel including a 180° bend with a 2:1 inlet and 1:1 aspect ratio outlet channel were validated against experimental results in terms of spatially resolved heat transfer distributions, pressure losses, and velocity distributions. The Numerical Domain consisted of one rib segment in the inlet channel and three ribs segments in the outlet channel to reduce the overall Numerical effort and allow for an extensive parametric study. The results showed good agreement for both heat transfer magnitudes and spatial distributions and the Numerical results captured the predominate flow physics resulting from the 180° bend. The production of Dean vortices and acceleration of the flow in the bend produced strongly increased heat transfer on both the ribbed and unribbed walls in the outlet channel in addition to increases due to the ribs. Numerical simulations were performed for a wide range of divider wall-to-tip wall distances, which influenced the position of the highest heat transfer levels on the outlet walls and changed the shape of the heat transfer distribution on the tip wall. Analysis of section averages of heat transfer in the bend and outlet channel showed a strong influence of the tip wall distance while no effect was seen upstream of the bend. A similarly large effect on pressure losses in the bend was observed with varying tip wall position. Trends in averaged heat transfer varied linearly with tip wall distance while pressure losses followed a non-linear trend, resulting in an optimum tip wall distance with respect to heat transfer efficiency.Copyright © 2008 by Alstom
