The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Philippe M Bardet - One of the best experts on this subject based on the ideXlab platform.
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Viscous Stress distribution over a wavy gas–liquid interface
International Journal of Multiphase Flow, 2020Co-Authors: Matthieu A Andre, Philippe M BardetAbstract:Abstract Viscous Stress contributes to momentum transfer between two phases, which plays an important role in both industrial applications and environmental processes. Near a wavy interface, the flow is modulated and produces a spatially non-uniform normal and tangential Viscous Stress. This study presents measurements of these Stresses at a liquid–gas interface populated with two-dimensional millimeter scale waves performed with multiphase particle image velocimetry. Large datasets enable conditional phase-averaging of the data based on wave steepness, which increases the precision of the results and allows statistical analysis. For the first time at this scale, the spatial distribution of normal and tangential Viscous Stress is obtained for a large range of wave steepness (ak = 0–1, with a the amplitude and k the wavenumber). As the steepness increases, the mean shear Stress over a wavelength decreases in magnitude, while the normal Viscous Stress increases. These trends are linear for ak 0.7, flow separation is observed in the gas phase near the troughs and drastically alters the Viscous Stress distribution.
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Viscous Stress distribution over a wavy gas liquid interface
International Journal of Multiphase Flow, 2017Co-Authors: Matthieu A Andre, Philippe M BardetAbstract:Abstract Viscous Stress contributes to momentum transfer between two phases, which plays an important role in both industrial applications and environmental processes. Near a wavy interface, the flow is modulated and produces a spatially non-uniform normal and tangential Viscous Stress. This study presents measurements of these Stresses at a liquid–gas interface populated with two-dimensional millimeter scale waves performed with multiphase particle image velocimetry. Large datasets enable conditional phase-averaging of the data based on wave steepness, which increases the precision of the results and allows statistical analysis. For the first time at this scale, the spatial distribution of normal and tangential Viscous Stress is obtained for a large range of wave steepness (ak = 0–1, with a the amplitude and k the wavenumber). As the steepness increases, the mean shear Stress over a wavelength decreases in magnitude, while the normal Viscous Stress increases. These trends are linear for ak 0.7, flow separation is observed in the gas phase near the troughs and drastically alters the Viscous Stress distribution.
Matthieu A Andre - One of the best experts on this subject based on the ideXlab platform.
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Viscous Stress distribution over a wavy gas–liquid interface
International Journal of Multiphase Flow, 2020Co-Authors: Matthieu A Andre, Philippe M BardetAbstract:Abstract Viscous Stress contributes to momentum transfer between two phases, which plays an important role in both industrial applications and environmental processes. Near a wavy interface, the flow is modulated and produces a spatially non-uniform normal and tangential Viscous Stress. This study presents measurements of these Stresses at a liquid–gas interface populated with two-dimensional millimeter scale waves performed with multiphase particle image velocimetry. Large datasets enable conditional phase-averaging of the data based on wave steepness, which increases the precision of the results and allows statistical analysis. For the first time at this scale, the spatial distribution of normal and tangential Viscous Stress is obtained for a large range of wave steepness (ak = 0–1, with a the amplitude and k the wavenumber). As the steepness increases, the mean shear Stress over a wavelength decreases in magnitude, while the normal Viscous Stress increases. These trends are linear for ak 0.7, flow separation is observed in the gas phase near the troughs and drastically alters the Viscous Stress distribution.
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Viscous Stress distribution over a wavy gas liquid interface
International Journal of Multiphase Flow, 2017Co-Authors: Matthieu A Andre, Philippe M BardetAbstract:Abstract Viscous Stress contributes to momentum transfer between two phases, which plays an important role in both industrial applications and environmental processes. Near a wavy interface, the flow is modulated and produces a spatially non-uniform normal and tangential Viscous Stress. This study presents measurements of these Stresses at a liquid–gas interface populated with two-dimensional millimeter scale waves performed with multiphase particle image velocimetry. Large datasets enable conditional phase-averaging of the data based on wave steepness, which increases the precision of the results and allows statistical analysis. For the first time at this scale, the spatial distribution of normal and tangential Viscous Stress is obtained for a large range of wave steepness (ak = 0–1, with a the amplitude and k the wavenumber). As the steepness increases, the mean shear Stress over a wavelength decreases in magnitude, while the normal Viscous Stress increases. These trends are linear for ak 0.7, flow separation is observed in the gas phase near the troughs and drastically alters the Viscous Stress distribution.
Guangcai Zhang - One of the best experts on this subject based on the ideXlab platform.
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discrete ellipsoidal statistical bgk model and burnett equations
Frontiers of Physics in China, 2018Co-Authors: Yudong Zhang, Guangcai Zhang, Aiguo Xu, Zhihua Chen, Pei WangAbstract:A new discrete Boltzmann model, the discrete ellipsoidal statistical Bhatnagar–Gross–Krook (ESBGK) model, is proposed to simulate nonequilibrium compressible flows. Compared with the original discrete BGK model, the discrete ES-BGK has a flexible Prandtl number. For the discrete ES-BGK model in the Burnett level, two kinds of discrete velocity model are introduced and the relations between nonequilibrium quantities and the Viscous Stress and heat flux in the Burnett level are established. The model is verified via four benchmark tests. In addition, a new idea is introduced to recover the actual distribution function through the macroscopic quantities and their space derivatives. The recovery scheme works not only for discrete Boltzmann simulation but also for hydrodynamic ones, for example, those based on the Navier–Stokes or the Burnett equations.
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discrete ellipsoidal statistical bgk model and burnett equations
arXiv: Fluid Dynamics, 2017Co-Authors: Yudong Zhang, Guangcai Zhang, Aiguo Xu, Zhihua Chen, Pei WangAbstract:To simulate non-equilibrium compressible flows, a new discrete Boltzmann model, discrete Ellipsoidal Statistical(ES)-BGK model, is proposed. Compared with the original discrete BGK model, the discrete ES-BGK has a flexible Prandtl number. For the discrete ES-BGK model in Burnett level, two kinds of discrete velocity model are introduced; the relations between non-equilibrium quantities and the Viscous Stress and heat flux in Burnett level are established. The model is verified via four benchmark tests. In addition, a new idea is introduced to recover the actual distribution function through the macroscopic quantities and their space derivatives. The recovery scheme works not only for discrete Boltzmann simulation but also for hydrodynamic ones, for example, based on the Navier-Stokes, the Burnett equations, etc.
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kinetic modeling of detonation and effects of negative temperature coefficient
Combustion and Flame, 2016Co-Authors: Yudong Zhang, Aiguo Xu, Guangcai ZhangAbstract:Abstract The kinetic modeling and simulation of reactive flows, especially for those with detonation, are further investigated. From the theoretical side, a new set of hydrodynamic equations are deduced, where the Viscous Stress tensor and heat flux are replaced by two non-equilibrium quantities that have been defined in our previous work. The two non-equilibrium quantities are referred to as Non-Organised Momentum Flux (NOMF) and Non-Organised Energy Flux (NOEF), respectively, here. The numerical results of Viscous Stress (heat flux) have a good agreement with those of NOMF (NOEF) near equilibrium state. Around sharp interfaces, the values of NOMF (NOEF) deviate reasonably from those of Viscous Stress (heat flux). Based on this hydrodynamic model, the relations between the two non-equilibrium quantities and entropy productions are established. Based on the discrete Boltzmann model, four kinds of detonation phenomena with different reaction rates, including Negative Temperature Coefficient (NTC) regime, are simulated and investigated. The differences of the four kinds of detonations are studied from three aspects: hydrodynamic quantities, non-equilibrium quantities and entropy productions. It is found that, the effects of NTC on hydrodynamic quantities are to lower the von-Neumann peaks of density, pressure, and velocity, to broaden the reaction zone, and to subdue the chemical reaction. It may also vanish the peak of temperature. Consequently, the effects of NTC are to widen the non-equilibrium regions and reduce the amplitude of the non-equilibrium effects in the reaction zone. Besides, it is also found that the (local) entropy production has three sources: the chemical reaction, NOEF and NOMF. As for the global entropy production in the system, the portion caused by reaction is much larger than the other two, and the portion caused by NOMF is larger than that by NOEF. Furthermore, the effect of NTC is to widen the region with entropy production caused by reaction and lower the global entropy productions caused by reaction, NOMF and NOEF, which means that NTC drives detonation closer to an isentropic process.
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kinetic modeling of detonation and effects of negative temperature coefficient
arXiv: Soft Condensed Matter, 2016Co-Authors: Yudong Zhang, Aiguo Xu, Guangcai ZhangAbstract:The kinetic modeling and simulation of reactive flows, especially for those with detonation, are further investigated. From the theoretical side, a new set of hydrodynamic equations are deduced, where the Viscous Stress tensor and heat flux are replaced by two non-equilibrium quantities that have been defined in our previous work. The two non-equilibrium quantities are referred to as NonOrganized Momentum Flux (NOMF) and Non-Organized Energy Flux (NOEF), respectively, here. The numerical results of Viscous Stress (heat flux) have a good agreement with those of NOMF (NOEF) near equilibrium state. Around sharp interfaces, the values of NOMF (NOEF) deviate reasonably from those of Viscous Stress (heat flux). Based on this hydrodynamic model, the relations between the two non-equilibrium quantities and entropy productions are established. Based on the discrete Boltzmann model, four kinds of detonation phenomena with different reaction rates, including Negative Temperature Coefficient (NTC) regime, are simulated and investigated. The differences of the four kinds of detonations are studied from three aspects: hydrodynamic quantities, non-equilibrium quantities and entropy productions.
Hyoung Gwon Choi - One of the best experts on this subject based on the ideXlab platform.
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temporal discretization of Viscous Stress terms of incompressible navier stokes equations with surface tension effect
Journal of Mechanical Science and Technology, 2015Co-Authors: Sanghun Choi, Hyoung Gwon ChoiAbstract:In this study, four temporal discretization methods for Viscous Stress terms were examined through the finite element method for incompressible Navier–Stokes equations with surface tension effect. The temporal stability and numerical accuracy of the four methods were evaluated in static and rising bubble benchmark problems with severe temporal restrictions caused by Viscous Stress terms. First, conservative and non-conservative discretization methods were compared in terms of stability and accuracy. The stability and accuracy of the numerical solutions were further investigated through three temporal discretization methods (i.e., fully implicit, semi-implicit, and fully explicit) for Viscous Stress terms. Nonconservative discretization may yield an incorrect solution although it provides a compact element matrix that reduces CPU time for matrix–vector multiplication. Among the three temporal discretization methods for the conservative treatment of Viscous Stress terms, the fully implicit method is recommended for cases with strong Viscous Stress. This method requires an element matrix that is larger than those of the other methods. However, the time-step limit caused by the explicit or semiimplicit treatment of Viscous Stress terms can be avoided.
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Temporal discretization of Viscous Stress terms of incompressible Navier–Stokes equations with surface tension effect
Journal of Mechanical Science and Technology, 2015Co-Authors: Sanghun Choi, Hyoung Gwon ChoiAbstract:In this study, four temporal discretization methods for Viscous Stress terms were examined through the finite element method for incompressible Navier–Stokes equations with surface tension effect. The temporal stability and numerical accuracy of the four methods were evaluated in static and rising bubble benchmark problems with severe temporal restrictions caused by Viscous Stress terms. First, conservative and non-conservative discretization methods were compared in terms of stability and accuracy. The stability and accuracy of the numerical solutions were further investigated through three temporal discretization methods (i.e., fully implicit, semi-implicit, and fully explicit) for Viscous Stress terms. Nonconservative discretization may yield an incorrect solution although it provides a compact element matrix that reduces CPU time for matrix–vector multiplication. Among the three temporal discretization methods for the conservative treatment of Viscous Stress terms, the fully implicit method is recommended for cases with strong Viscous Stress. This method requires an element matrix that is larger than those of the other methods. However, the time-step limit caused by the explicit or semiimplicit treatment of Viscous Stress terms can be avoided.
Wenbo Chen - One of the best experts on this subject based on the ideXlab platform.
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time and strain rate effects on Viscous Stress strain behavior of plasticine material
International Journal of Geomechanics, 2017Co-Authors: Weiqiang Feng, Fei Tong, Wenbo ChenAbstract:AbstractA plasticine material exhibits the characterized Viscous Stress–strain behavior with some similarity to the behavior of clayey soils. This paper presents a series of experimental tests, which include oedometer tests, isotropic creep tests, and triaxial multistrain rate compression tests, on a plasticine material. The test study focuses on effects of time and strain rate on Viscous Stress–strain behavior of the plasticine material under one-dimensional (1D) straining, isotropic Stressing, and triaxial compression conditions. Values of compression index (Cce), rebounding index (Cre), and creep coefficient (Cαe) are obtained from the 1D straining and 1D Stressing test data. The plasticine material has no primary consolidation period, and creep occurs from the beginning. Values of Cce, Cre, and Cαe are smaller than those of the soft clays. The triaxial multistrain rate compression test data show that the Stress–strain behavior of the plasticine depends on the strain rates and the confining pressures. ...
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Time and Strain-Rate Effects on Viscous Stress–Strain Behavior of Plasticine Material
International Journal of Geomechanics, 2017Co-Authors: Weiqiang Feng, Fei Tong, Wenbo ChenAbstract:AbstractA plasticine material exhibits the characterized Viscous Stress–strain behavior with some similarity to the behavior of clayey soils. This paper presents a series of experimental tests, which include oedometer tests, isotropic creep tests, and triaxial multistrain rate compression tests, on a plasticine material. The test study focuses on effects of time and strain rate on Viscous Stress–strain behavior of the plasticine material under one-dimensional (1D) straining, isotropic Stressing, and triaxial compression conditions. Values of compression index (Cce), rebounding index (Cre), and creep coefficient (Cαe) are obtained from the 1D straining and 1D Stressing test data. The plasticine material has no primary consolidation period, and creep occurs from the beginning. Values of Cce, Cre, and Cαe are smaller than those of the soft clays. The triaxial multistrain rate compression test data show that the Stress–strain behavior of the plasticine depends on the strain rates and the confining pressures. ...
