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  • American Institute of Physics (AIP)  (16)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1766-1771 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Most subgrid-scale (SGS) models for large-eddy simulations (LES) are absolutely dissipative (that is, they remove energy from the large scales at each point in the physical space). The actual SGS stresses, however, may transfer energy to the large scales (backscatter) at a given location. Recent work on the LES of transitional flows [Piomelli et al., Phys. Fluids A 2, 257 (1990)] has shown that failure to account for this phenomenon can cause inaccurate prediction of the growth of the perturbations. Direct numerical simulations of transitional and turbulent channel flow and compressible isotropic turbulence are used to study the backscatter phenomenon. In all flows considered roughly 50% of the grid points were experiencing backscatter when a Fourier cutoff filter was used. The backscatter fraction was less with a Gaussian filter, and intermediate with a box filter in physical space. Moreover, the backscatter and forward scatter contributions to the SGS dissipation were comparable, and each was often much larger than the total SGS dissipation. The SGS dissipation (normalized by total dissipation) increased with filter width almost independently of filter type. The amount of backscatter showed an increasing trend with Reynolds number. In the near-wall region of the channel, events characterized by strong Reynolds shear stress correlated fairly well with areas of high SGS dissipation (both forward and backward). In compressible isotropic turbulence similar results were obtained, independent of fluctuation Mach number.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3128-3128 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 609-611 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of large eddy simulation (LES) of the Navier–Stokes equations are used to evaluate the validity of Taylor's hypothesis of frozen turbulence, which states that the time derivative of some instantaneous quantity is proportional to its derivative in the streamwise direction, for incompressible plane channel flow. Time and space derivatives in the streamwise direction of the velocity components are, in fact, found to be well correlated. Root-mean-square fluctuations of the terms in Taylor's hypothesis also support the validity of this hypothesis above the buffer layer. The good agreement between LES and experimental results indicates that errors in the evaluation of derivatives in the streamwise direction are due mostly to insufficient resolution.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 2551-2551 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1484-1490 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic subgrid-scale eddy viscosity model has been used in the large-eddy simulation of the turbulent flow in a plane channel for Reynolds numbers based on friction velocity and channel half-width ranging between 200 and 2000, a range including values significantly higher than in previous simulations. The computed wall stress, mean velocity, and Reynolds stress profiles compare very well with experimental and direct simulation data. Comparison of higher moments is also satisfactory. Although the grid in the near-wall region is fairly coarse, the results are quite accurate: the turbulent kinetic energy peaks at y+(approximately-equal-to)12, and the near-wall behavior of the resolved stresses is captured accurately. The model coefficient is o(10−3) in the buffer layer and beyond, where the cutoff wave numbers are in the decaying region of the spectra; in the near-wall region the cutoff wave numbers are nearer the energy-containing range, and the resolved turbulent stresses become a constant fraction of the resolved stresses. This feature is responsible for the correct near-wall behavior of the model coefficient. In the near-wall region the eddy viscosity is reduced to account for the energy transfer from small to large scales that may occur locally.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1760-1765 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One major drawback of the eddy viscosity subgrid-scale stress models used in large-eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid-scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid-scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near-wall region of a turbulent boundary layer. The results of large-eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 257-265 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of the subgrid-scale fields in plane channel flow has been studied at various stages of the transition process to turbulence. The residual stress and subgrid-scale dissipation calculated using velocity fields generated by direct numerical simulations of the Navier–Stokes equations are significantly different from their counterparts in turbulent flows. The subgrid scale dissipation changes sign over extended areas of the channel, indicating energy flow from the small scales to the large scales. This reversed energy cascade becomes less pronounced at the later stages of transition. Standard residual stress models of the Smagorinsky type are excessively dissipative. Rescaling the model constant improves the prediction of the total (integrated) subgrid scale dissipation, but not that of the local one. Despite the somewhat excessive dissipation of the rescaled Smagorinsky model, the results of a large-eddy simulation of transition on a flat-plate boundary layer compare quite well with those of a direct simulation, and require only a small fraction of the computational effort.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 764-766 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Turbulence-producing events in turbulent channel flow were found to be predominantly associated with asymmetric vortical structures rather than pairs of counter-rotating structures. An asymmetry-preserving averaging scheme was devised, allowing a picture of the "average'' structure that more closely resembles the instantaneous one to be obtained. In addition, these structures were found to persist for long distances with little change while convecting downstream.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3471-3474 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapid distortion theory is applied to study the response of homogeneous turbulence to imposed arbitrary irrotational mean strains. Expressions useful in turbulence modeling, such as the Reynolds stresses and vorticity correlations, have been obtained.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2740-2748 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An a priori study of the subgrid-scale (SGS) stresses and dissipation in two nonequilibrium, wall-bounded flows is carried out. The velocity fields were computed by direct simulations of two- and three-dimensional boundary layers obtained, respectively, by a sudden change in the Reynolds number and by an impulsive motion in the spanwise direction of the lower wall of a plane channel in fully developed turbulent flow conditions. Several realizations of the transient period of the flow were examined. The SGS stresses react to the imposition of the secondary shear more rapidly than the large-scale ones, and return to equilibrium before the resolved stresses do. In general, the subgrid scales are less sensitive than the large ones to the near-wall and nonequilibrium effects. Scale-similar and dynamic models appear well-suited to reproduce the correlation between resolved Reynolds stress production and events with significant production of SGS energy. © 1997 American Institute of Physics.
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