The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Marcus Herrmann - One of the best experts on this subject based on the ideXlab platform.
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A Dual Scale Approach for Modeling Turbulent Liquid/Gas Phase Interfaces
Turbulent Cascades II, 2019Co-Authors: Dominic Kedelty, James Uglietta, Marcus HerrmannAbstract:Advances to a dual-scale modeling approach [1] are presented to describe turbulent Phase Interface dynamics in a large-eddy-simulation-type spatial filtering context. Spatial filtering of the governing equations introduces several sub-filter terms that require modeling. Instead of developing individual closure-models for the terms associated with the Interface, the dual-scale approach uses an exact closure by explicitly filtering a fully resolved realization of the Phase Interface. This resolved realization is maintained on a high-resolution over-set mesh. The advection equation for the Phase Interface on this DNS scale requires a model for the fully resolved Interface advection velocity. This velocity is the sum of the filter scale LES velocity, available from the LES flow solver, and the sub-filter velocity fluctuation. The sub-filter velocity fluctuation is due to sub-filter turbulent eddies, reconstructed using a local fractal interpolation technique [2]. Results of the dual-scale model are compared to recent DNS of unit density and viscosity contrast Interfaces in homogeneous isotropic turbulence without surface tension [3]. Open image in new window
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A Dual-Scale LES Subgrid Model for Turbulent Liquid/Gas Phase Interface Dynamics
Volume 1: Symposia, 2015Co-Authors: Marcus HerrmannAbstract:Turbulent liquid/gas Phase Interface dynamics are at the core of many applications. For example, in atomizing flows, the properties of the resulting liquid spray are determined by the interplay of fluid and surface tension forces. The resulting dynamics typically span 4–6 orders of magnitude in length scales, making direct numerical simulations exceedingly expensive. This motivates the need for modeling approaches based on spatial filtering or ensemble averaging. In this paper, a dual-scale modeling approach is presented to describe turbulent two-Phase Interface dynamics in a large-eddy-simulation-type spatial filtering context. To close the unclosed terms related to the Phase Interface arising from filtering the Navier-Stokes equation, a resolved realization of the Phase Interface dynamics is explicitly filtered. This resolved realization is maintained on a high-resolution over-set mesh using a Refined Local Surface Grid approach [1] employing an un-split, geometric, bounded, and conservative Volume-of-Fluid method [2]. The required model for the resolved realization of the Interface advection velocity includes the effects of sub-filter surface tension, dissipation, and turbulent eddies. Results of the dual-scale model are compared to recent direct numerical simulations of an Interface in homogeneous isotropic turbulence [3].Copyright © 2015 by ASME
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a parallel eulerian Interface tracking lagrangian point particle multi scale coupling procedure
Journal of Computational Physics, 2010Co-Authors: Marcus HerrmannAbstract:This paper presents a parallel Eulerian/Lagrangian multi-scale coupling procedure for two-Phase flows. At the fully resolved scale, the dynamically evolving Phase Interface is tracked using a Eulerian approach. In regions of the flow, where the Phase Interface geometry can no longer be resolved adequately, separated, small scale liquid structures are described by a Lagrangian point particle approach. The coupling procedure of these two descriptions consists of an efficient parallel algorithm that identifies tracked liquid candidate structures, removes them from the resolved Eulerian description, and inserts them into the Lagrangian description preserving their position, mass, momentum, and lower order shape. While in principle applicable to level set, Volume of Fluid, and marker particle Interface tracking methods for the fully resolved scale, this paper focuses on examples from atomization simulations using the refined level set grid method.
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A Large Eddy Simulation Subgrid Model for Turbulent Phase Interface Dynamics
2009Co-Authors: Marcus Herrmann, Mikhael GorokhovskiAbstract:In this paper we report on the outline of a Large Eddy Simulation subgrid model for liquid/gas Phase Interface dynamics. A key feature of the proposed model is to take the subgrid Phase Interface dynamics fully into account by employing a dual-scale approach. Instead of modeling the LES subgrid Phase Interface geometry, we fully resolve it on an auxillary grid using the Rened Level Set Grid approach (Herrmann 2008). We then propose to model the LES subgrid velocity on the auxillary grid needed to move the fully resolved Phase Interface, by solving a dedicated PDE for its evolution near the Phase Interface. This PDE contains three dierent contributions. First, the sublter turbulent eddies are taken into account by modeling the sublter acceleration in lines of Oboukhovs log-normality conjecture on the stochastic eld of ". The second term, a velocity increment due to the relative motion between the two Phases is modeled deriving renormalized velocity boundary condition at the Phase Interface. The nal term, due to sublter surface tension induced sublter velocities is modeled following a Taylor analogy. Knowing the fully resolved Phase Interface geometry, all previously unclosed terms in the ltered Navier-Stokes equations can be directly closed using explicit ltering.
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a eulerian level set vortex sheet method for two Phase Interface dynamics
Journal of Computational Physics, 2005Co-Authors: Marcus HerrmannAbstract:A Eulerian fixed grid approach to simulate the dynamics of two-Phase Interfaces in the presence of surface tension forces is presented. This level set/vortex sheet method consists of a simplified system of equations that contain individual source terms describing the relevant physical processes at the Phase Interface explicitly. Hence, this approach provides a framework that will allow for a simplified subsequent modeling of Phase Interface dynamics in turbulent environments. In the presented level set/vortex sheet method, the location and the motion of the Phase Interface are captured by a level set equation. Topological changes of the Interface, like breakup or merging, are thus handled automatically. Assuming that all vorticity is concentrated at the Phase Interface, the Phase Interface itself constitutes a vortex sheet with varying vortex sheet strength. The Eulerian transport equation for the vortex sheet strength is derived by combining its Lagrangian formulation with the level set equation. The resulting differential equation then contains source terms accounting for the stretching of the Interface and the influence of surface tension, thus allowing for a detailed study of each effect individually. The results of three test problems, namely the roll-up of a vortex sheet without surface tension, the growth of the Kelvin-Helmholtz instability in the linear regime, and the long-time evolution of the Kelvin-Helmholtz instability are presented.
Rongzong Huang - One of the best experts on this subject based on the ideXlab platform.
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Phase Interface effects in the total enthalpy based lattice boltzmann model for solid liquid Phase change
Journal of Computational Physics, 2015Co-Authors: Rongzong HuangAbstract:Abstract In this paper, Phase Interface effects, including the differences in thermophysical properties between solid and liquid Phases and the numerical diffusion across Phase Interface, are investigated for the recently developed total enthalpy-based lattice Boltzmann model for solid–liquid Phase change, which has high computational efficiency by avoiding iteration procedure and linear equation system solving. For the differences in thermophysical properties (thermal conductivity and specific heat) between solid and liquid Phases, a novel reference specific heat is introduced to improve the total enthalpy-based lattice Boltzmann model, which makes the thermal conductivity and specific heat decoupled. Therefore, the differences in thermal conductivity and specific heat can be handled by the dimensionless relaxation time and equilibrium distribution function, respectively. As for the numerical diffusion across Phase Interface, it is revealed for the first time and found to be induced by solid–liquid Phase change. To reduce such numerical diffusion, multiple-relaxation-time collision scheme is exploited, and a special value (one fourth) for the so-called “magic” parameter, a combination of two relaxation parameters, is found. Numerical tests show that the differences in thermophysical properties can be correctly handled and the numerical diffusion across Phase Interface can be dramatically reduced. Finally, theoretical analyses are carried out to offer insights into the roles of the reference specific heat and “magic” parameter in the treatments of Phase Interface effects.
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Phase Interface effects in the total enthalpy-based lattice Boltzmann model for solid–liquid Phase change
Journal of Computational Physics, 2015Co-Authors: Rongzong HuangAbstract:Abstract In this paper, Phase Interface effects, including the differences in thermophysical properties between solid and liquid Phases and the numerical diffusion across Phase Interface, are investigated for the recently developed total enthalpy-based lattice Boltzmann model for solid–liquid Phase change, which has high computational efficiency by avoiding iteration procedure and linear equation system solving. For the differences in thermophysical properties (thermal conductivity and specific heat) between solid and liquid Phases, a novel reference specific heat is introduced to improve the total enthalpy-based lattice Boltzmann model, which makes the thermal conductivity and specific heat decoupled. Therefore, the differences in thermal conductivity and specific heat can be handled by the dimensionless relaxation time and equilibrium distribution function, respectively. As for the numerical diffusion across Phase Interface, it is revealed for the first time and found to be induced by solid–liquid Phase change. To reduce such numerical diffusion, multiple-relaxation-time collision scheme is exploited, and a special value (one fourth) for the so-called “magic” parameter, a combination of two relaxation parameters, is found. Numerical tests show that the differences in thermophysical properties can be correctly handled and the numerical diffusion across Phase Interface can be dramatically reduced. Finally, theoretical analyses are carried out to offer insights into the roles of the reference specific heat and “magic” parameter in the treatments of Phase Interface effects.
Yang Yang - One of the best experts on this subject based on the ideXlab platform.
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Effects of the Phase Interface on spallation damage nucleation and evolution in multiPhase alloy
Journal of Alloys and Compounds, 2018Co-Authors: Yang Yang, Can Wang, Xingzhi Chen, Kaiguo ChenAbstract:Abstract The spall behaviors of Cu-34%Zn-3%Pb leaded brass samples with annealing and cryogenic treating conditions were dynamic loaded using one-stage light gas gun experiments under ∼1.515 GPa shock pressure. The effects of α/β Phase Interface and Pb/matrix Phase Interface on dynamic damage nucleation, growth, and coalescence in leaded brass specimens were investigated by multidimensional testing techniques. Experiment results showed that voids of incipient spall were mainly nucleated in the interior of the Pb-Phases with signs of melting, and a small number of voids were nucleated in α-Phase, and both are not nucleated at the Interface which contradicts the damage fracture theory under quasi-static loading. Due to the effect of reflection and transmission of shock wave at the Phase Interface, when the shock wave propagates from α-Phase with higher impedance to Pb-Phase or β-Phase with lower impedance, a tensile pulse will be formed within α-Phase. If the tensile pulse has sufficient amplitude voids would be nucleated in α-Phase. On the other hand, it is considered that the asymmetry high compression zones in the center of the lead-Phase with low impedance were formed by the shock wave convergence effects of matrix/lead quasi-spherical Interface, which caused adiabatic temperature rise exceeded melting point of lead due to severe plastic deformation, and finally led to local melting and void nucleation in the center of the lead-Phase rather than the tensile stress.
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Effects of the Phase Interface on initial spallation damage nucleation and evolution in dual Phase titanium alloy
Materials Science and Engineering: A, 2018Co-Authors: Yang Yang, Can Wang, Z. Jiang, Tiegang Tang, Hai-yan ZhangAbstract:Abstract The Ti-6Al-4V dual Phase alloy samples were dynamic loaded by one-stage light gas gun experiment and samples with initial spallation were softly recovered. During the loading experiment, the velocity of free surface particles was measured by photonic doppler velocimetry (PDV). The effect of α/β Phase Interface on nucleation, growth, and coalescence of dynamic damage in Ti-6Al-4V were investigated by 2-D or 3-D testing techniques, such as optical microscopy(OM), x-ray computer tomography(XRCT), and electron backscattered diffraction(EBSD). The results showed that the majority of voids were nucleated within α Phases, rather than on the α/β Phase Interface as predicted by quasi-static damage theory. Due to the effects of reflection and transmission of shock wave at the Phase Interface, a tensile pulse would be formed within α Phase when the shock wave transmit from α Phase with high impedance to β Phase with low impedance. When this tensile pulse was large enough, voids would be formed within α Phase. The analyses of OM and XRCT indicated that the voids at the beginning of nucleation were nearly spherical, then grew up along the direction of 45° with the shock loading direction, and finally the rod-shaped voids were formed. Besides, the voids were not randomly nucleated within α Phase, and the EBSD analysis showed that the voids were mainly nucleated at grain boundary triple points which composed of grains with large difference of Taylor Factor(TF) value within α Phase. This is because the difference of plastic deformation capacity of this grains is larger, and it is easier to produce stress concentration. Thus these sites became the prior nucleation position of voids.
Kaiguo Chen - One of the best experts on this subject based on the ideXlab platform.
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Effects of the Phase Interface on spallation damage nucleation and evolution in multiPhase alloy
Journal of Alloys and Compounds, 2018Co-Authors: Yang Yang, Can Wang, Xingzhi Chen, Kaiguo ChenAbstract:Abstract The spall behaviors of Cu-34%Zn-3%Pb leaded brass samples with annealing and cryogenic treating conditions were dynamic loaded using one-stage light gas gun experiments under ∼1.515 GPa shock pressure. The effects of α/β Phase Interface and Pb/matrix Phase Interface on dynamic damage nucleation, growth, and coalescence in leaded brass specimens were investigated by multidimensional testing techniques. Experiment results showed that voids of incipient spall were mainly nucleated in the interior of the Pb-Phases with signs of melting, and a small number of voids were nucleated in α-Phase, and both are not nucleated at the Interface which contradicts the damage fracture theory under quasi-static loading. Due to the effect of reflection and transmission of shock wave at the Phase Interface, when the shock wave propagates from α-Phase with higher impedance to Pb-Phase or β-Phase with lower impedance, a tensile pulse will be formed within α-Phase. If the tensile pulse has sufficient amplitude voids would be nucleated in α-Phase. On the other hand, it is considered that the asymmetry high compression zones in the center of the lead-Phase with low impedance were formed by the shock wave convergence effects of matrix/lead quasi-spherical Interface, which caused adiabatic temperature rise exceeded melting point of lead due to severe plastic deformation, and finally led to local melting and void nucleation in the center of the lead-Phase rather than the tensile stress.
Can Wang - One of the best experts on this subject based on the ideXlab platform.
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Effects of the Phase Interface on spallation damage nucleation and evolution in multiPhase alloy
Journal of Alloys and Compounds, 2018Co-Authors: Yang Yang, Can Wang, Xingzhi Chen, Kaiguo ChenAbstract:Abstract The spall behaviors of Cu-34%Zn-3%Pb leaded brass samples with annealing and cryogenic treating conditions were dynamic loaded using one-stage light gas gun experiments under ∼1.515 GPa shock pressure. The effects of α/β Phase Interface and Pb/matrix Phase Interface on dynamic damage nucleation, growth, and coalescence in leaded brass specimens were investigated by multidimensional testing techniques. Experiment results showed that voids of incipient spall were mainly nucleated in the interior of the Pb-Phases with signs of melting, and a small number of voids were nucleated in α-Phase, and both are not nucleated at the Interface which contradicts the damage fracture theory under quasi-static loading. Due to the effect of reflection and transmission of shock wave at the Phase Interface, when the shock wave propagates from α-Phase with higher impedance to Pb-Phase or β-Phase with lower impedance, a tensile pulse will be formed within α-Phase. If the tensile pulse has sufficient amplitude voids would be nucleated in α-Phase. On the other hand, it is considered that the asymmetry high compression zones in the center of the lead-Phase with low impedance were formed by the shock wave convergence effects of matrix/lead quasi-spherical Interface, which caused adiabatic temperature rise exceeded melting point of lead due to severe plastic deformation, and finally led to local melting and void nucleation in the center of the lead-Phase rather than the tensile stress.
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Effects of the Phase Interface on initial spallation damage nucleation and evolution in dual Phase titanium alloy
Materials Science and Engineering: A, 2018Co-Authors: Yang Yang, Can Wang, Z. Jiang, Tiegang Tang, Hai-yan ZhangAbstract:Abstract The Ti-6Al-4V dual Phase alloy samples were dynamic loaded by one-stage light gas gun experiment and samples with initial spallation were softly recovered. During the loading experiment, the velocity of free surface particles was measured by photonic doppler velocimetry (PDV). The effect of α/β Phase Interface on nucleation, growth, and coalescence of dynamic damage in Ti-6Al-4V were investigated by 2-D or 3-D testing techniques, such as optical microscopy(OM), x-ray computer tomography(XRCT), and electron backscattered diffraction(EBSD). The results showed that the majority of voids were nucleated within α Phases, rather than on the α/β Phase Interface as predicted by quasi-static damage theory. Due to the effects of reflection and transmission of shock wave at the Phase Interface, a tensile pulse would be formed within α Phase when the shock wave transmit from α Phase with high impedance to β Phase with low impedance. When this tensile pulse was large enough, voids would be formed within α Phase. The analyses of OM and XRCT indicated that the voids at the beginning of nucleation were nearly spherical, then grew up along the direction of 45° with the shock loading direction, and finally the rod-shaped voids were formed. Besides, the voids were not randomly nucleated within α Phase, and the EBSD analysis showed that the voids were mainly nucleated at grain boundary triple points which composed of grains with large difference of Taylor Factor(TF) value within α Phase. This is because the difference of plastic deformation capacity of this grains is larger, and it is easier to produce stress concentration. Thus these sites became the prior nucleation position of voids.