The Experts below are selected from a list of 195837 Experts worldwide ranked by ideXlab platform
Shiyi Chen - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of spanwise rotating turbulent channel flow with dynamic variants of eddy viscosity Model
Physics of Fluids, 2018Co-Authors: Zhou Jiang, Zhenhua Xia, Yipeng Shi, Shiyi ChenAbstract:A fully developed spanwise rotating turbulent channel flow has been numerically investigated utilizing large-eddy simulation. Our focus is to assess the performances of the dynamic variants of eddy viscosity Models, including dynamic Vreman’s Model (DVM), dynamic wall adapting local eddy viscosity (DWALE) Model, dynamic σ (Dσ) Model, and the dynamic volumetric strain-stretching (DVSS) Model, in this canonical flow. The results with dynamic Smagorinsky Model (DSM) and direct numerical simulations (DNS) are used as references. Our results show that the DVM has a wrong asymptotic behavior in the near wall region, while the other three Models can correctly predict it. In the high rotation case, the DWALE can get reliable mean velocity profile, but the turbulence intensities in the wall-normal and spanwise directions show clear deviations from DNS data. DVSS exhibits poor predictions on both the mean velocity profile and turbulence intensities. In all three cases, Dσ performs the best.
Haecheon Choi - One of the best experts on this subject based on the ideXlab platform.
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a dynamic global subgrid scale Model for large eddy simulation of scalar transport in complex turbulent flows
Journal of Mechanical Science and Technology, 2012Co-Authors: Jungil Lee, Haecheon ChoiAbstract:In the present study, a dynamic global subgrid-scale eddy diffusivity Model for large eddy simulation of scalar transport in complex turbulent flows is proposed by generalizing the dynamic global subgrid-scale eddy viscosity Model [Phys. Fluids, 18 125109 (2006) and Phys. Fluids, 22 075106 (2010)]. The global Model coefficient in the subgrid-scale Model is determined by a dynamic procedure based on the Germano identity such that the Model coefficient is globally constant in space but varies only in time. Large eddy simulations of passive scalar transport in turbulent channel flow, turbulent boundary layer, and turbulent ribbed channel flow are conducted and the proposed Model shows an excellent performance for all the flows considered. Since the proposed Model requires no ad hoc clipping and/or averaging over a homogeneous direction, it can be readily applied to large eddy simulation of scalar transport in complex turbulent flows.
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A dynamic subgrid-scale eddy viscosity Model with a global Model coefficient
Physics of Fluids, 2006Co-Authors: Noma Park, Sungwon Lee, Jungil Lee, Haecheon ChoiAbstract:In the present study, a dynamic subgrid-scale eddy viscosity Model is proposed for large eddy simulation of turbulent flows in complex geometry. A subgrid-scale eddy viscosity Model recently proposed by Vreman [Phys. Fluids 16, 3670 (2004)] which guarantees theoretically zero subgrid-scale dissipation for various laminar shear flows, is considered as a base Model. A priori tests with the original Vreman Model show that it predicts the correct profile of subgrid-scale dissipation in turbulent channel flow but the optimal Model coefficient is far from universal. A dynamic procedure of determining the Model coefficient is proposed based on the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation. An important feature of the proposed procedure is that the Model coefficient determined is globally constant in space but varies only in time. A posteriori tests of the proposed dynamic Model are conducted through large eddy simulations of forced isotropic turbulence at Reλ=103, tur...
Donghyun You - One of the best experts on this subject based on the ideXlab platform.
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a dynamic global coefficient subgrid scale eddy viscosity Model for large eddy simulation in complex geometries
Physics of Fluids, 2007Co-Authors: Donghyun YouAbstract:An improvement of the dynamic procedure of Park et al. [Phys. Fluids 18, 125109 (2006)] for closure of the subgrid-scale Eddy-Viscosity Model developed by Vreman [Phys. Fluids 16, 3670 (2004)] is proposed. The Model coefficient which is globally constant in space but varies in time is dynamically determined assuming the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation of which utilization was proposed by Park et al. Like the Vreman Model with a fixed coefficient and the dynamic-coefficient Model of Park et al., the present Model predicts zero Eddy-Viscosity in regions where the vanishing eddy viscosity is theoretically expected. The present dynamic Model is especially suitable for large-eddy simulation in complex geometries since it does not require any ad hoc spatial and temporal averaging or clipping of the Model coefficient for numerical stabilization and more importantly, requires only a single-level test filter in contrast to the dynamic Model of Park et al., whi...
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application of a dynamic global coefficient subgrid scale Model for large eddy simulation in complex geometries
ASME JSME 2007 5th Joint Fluids Engineering Conference, 2007Co-Authors: Donghyun YouAbstract:The application of a dynamic global-coefficient subgrid-scale Eddy-Viscosity Model for large-eddy simulation in complex geometries is presented. The Model employs a dynamic procedure for closure of the subgrid-scale Eddy-Viscosity Model developed by Vreman [Phys. Fluids 16 , 3670 (2004)]. The Model coefficient which is globally constant in space but varies in time is dynamically determined assuming the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation of which utilization was proposed by Park et al. [Phys. Fluids 18 , 125109 (2006)]. Like the Vreman’s Model with a fixed coefficient and the dynamic-coefficient Model of Park et al., the present Model predicts zero Eddy-Viscosity in regions where the vanishing eddy viscosity is theoretically expected. The present dynamic Model is especially suitable for large-eddy simulation in complex geometries since it does not require any ad hoc spatial and temporal averaging or clipping of the Model coefficient for numerical stabilization and requires only a single-level test filter.Copyright © 2007 by ASME
Gianluca Iaccarino - One of the best experts on this subject based on the ideXlab platform.
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the deviation from parallel shear flow as an indicator of linear eddy viscosity Model inaccuracy
Physics of Fluids, 2014Co-Authors: Catherine Gorle, Johan Larsson, Michael Emory, Gianluca IaccarinoAbstract:A marker function designed to indicate in which regions of a generic flow field the results from linear Eddy-Viscosity turbulence Models are plausibly inaccurate is introduced. The marker is defined to identify regions that deviate from parallel shear flow. For two different flow fields it is shown that these regions largely coincide with regions where the prediction of the Reynolds stress divergence is inaccurate. The marker therefore offers a guideline for interpreting results obtained from Reynolds-averaged Navier-Stokes simulations and provides a basis for the further development of turbulence Model-form uncertainty quantification methods.
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A subgrid-scale Eddy-Viscosity Model based on the volumetric strain-stretching
Physics of Fluids, 2014Co-Authors: Sungmin Ryu, Gianluca IaccarinoAbstract:We propose a novel subgrid-scale (SGS) Eddy-Viscosity Model for large eddy simulation (LES) to accurately reproduce the effect of subgrid stresses on the resolved scales. The developed SGS Model is based on the second-order volumetric strain-stretching (VSS) tensor, which is constructed by the multiplication of diagonal components of the strain-rate tensor with its off-diagonal components. The proposed VSS-Model is validated in typical flow cases: freely decaying isotropic turbulence, incompressible turbulent channel flow at Reτ = 395, compressible turbulent channel flows at Ma = 1.5 and Reτ = 221, and Ma = 3.0 and Reτ = 556. LESs with the dynamic Smagorinsky Model and the Vreman Model are also performed to compare the performance of the VSS-Model. The proposed Model correctly recovers cubic wall behavior in the vicinity of solid boundaries in incompressible flow regime, and it has no limitation in its application to geometrically complex flows.
Charles Meneveau - One of the best experts on this subject based on the ideXlab platform.
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a lagrangian dynamic subgrid scale Model of turbulence
Journal of Fluid Mechanics, 1996Co-Authors: Charles Meneveau, Thomas S Lund, William H CabotAbstract:The dynamic Model for large-eddy simulation of turbulence samples information from the resolved velocity field in order to optimize subgrid-scale Model coefficients. When the method is used in conjunction with the Smagorinsky Eddy-Viscosity Model, and the sampling process is formulated in a spatially local fashion, the resulting coefficient field is highly variable and contains a significant fraction of negative values. Negative eddy viscosity leads to computational instability and as a result the Model is always augmented with a stabilization mechanism. In most applications the Model is stabilized by averaging the relevant equations over directions of statistical homogeneity. While this approach is effective, and is consistent with the statistical basis underlying the Eddy-Viscosity Model, it is not applicable to complex-geometry inhomogeneous flows. Existing local formulations, intended for inhomogeneous flows, are most commonly stabilized by artificially constraining the coefficient to be positive. In this paper we introduce a new dynamic Model formulation, that combines advantages of the statistical and local approaches. We propose to accumulate the required averages over flow pathlines rather than over directions of statistical homogeneity. This procedure allows the application of the dynamic Model with averaging to in-homogeneous flows in complex geometries. We analyse direct numerical simulation data to document the effects of such averaging on the Smagorinsky coefficient. The characteristic Lagrangian time scale over which the averaging is performed is chosen based on measurements of the relevant Lagrangian autocorrelation functions, and on the requirement that the Model be purely dissipative, guaranteeing numerical stability when coupled with the Smagorinsky Model. The formulation is tested in forced and decaying isotropic turbulence and in fully developed and transitional channel flow. In homogeneous flows, the results are similar to those of the volume-averaged dynamic Model, while in channel flow, the predictions are slightly superior to those of the spatially (planar) averaged dynamic Model. The relationship between the Model and vortical structures in isotropic turbulence, as well as ejection events in channel flow, is investigated. Computational overhead is kept small (about 10% above the CPU requirements of the spatially averaged dynamic Model) by using an approximate scheme to advance the Lagrangian tracking through first-order Euler time integration and linear interpolation in space.
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a lagrangian dynamic subgrid scale Model of turbulence
Journal of Fluid Mechanics, 1996Co-Authors: Charles Meneveau, Thomas S Lund, William CabotAbstract:The dynamic Model for large-eddy simulation of turbulence samples information from the resolved velocity field in order to optimize subgrid-scale Model coefficients. When the method is used in conjunction with the Smagorinsky Eddy-Viscosity Model, and the sampling process is formulated in a spatially local fashion, the resulting coefficient field is highly variable and contains a significant fraction of negative values. Negative eddy viscosity leads to computational instability and as a result the Model is always augmented with a stabilization mechanism. In most applications the Model is stabilized by averaging the relevant equations over directions of statistical homogeneity. While this approach is effective, and is consistent with the statistical basis underlying the Eddy-Viscosity Model, it is not applicable to complex-geometry inhomogeneous flows. Existing local formulations, intended for inhomogeneous flows, are most commonly stabilized by artificially constraining the coefficient to be positive. In this paper we introduce a new dynamic Model formulation, that combines advantages of the statistical and local approaches. We propose to accumulate the required averages over flow pathlines rather than over directions of statistical homogeneity. This procedure allows the application of the dynamic Model with averaging to in-homogeneous flows in complex geometries. We analyse direct numerical simulation data to document the effects of such averaging on the Smagorinsky coefficient. The characteristic Lagrangian time scale over which the averaging is performed is chosen based on measurements of the relevant Lagrangian autocorrelation functions, and on the requirement that the Model be purely dissipative, guaranteeing numerical stability when coupled with the Smagorinsky Model. The formulation is tested in forced and decaying isotropic turbulence and in fully developed and transitional channel flow. In homogeneous flows, the results are similar to those of the volume-averaged dynamic Model, while in channel flow, the predictions are slightly superior to those of the spatially (planar) averaged dynamic Model. The relationship between the Model and vortical structures in isotropic turbulence, as well as ejection events in channel flow, is investigated. Computational overhead is kept small (about 10% above the CPU requirements of the spatially averaged dynamic Model) by using an approximate scheme to advance the Lagrangian tracking through first-order Euler time integration and linear interpolation in space.
