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  • 1
    Electronic Resource
    Electronic Resource
    A nonequilibrium fixed-parameter subgrid-scale model obeying the near-wall asymptotic constraint (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 2338-2344 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A subgrid-scale (SGS) model is presented with two fixed nondimensional model parameters adopted, which is in the same line of the Smagorinsky model combined with Van Driest's wall damping function. The proposed model, however, possesses two features that are typical of the dynamic SGS modeling. One is that it is not based on the equilibrium assumption about the SGS-energy production and dissipation rates. The other is that the model is not dependent on a wall-unit coordinate and obeys the correct near-wall asymptotic behavior, unlike the Smagorinsky–Van Driest model. This model is applied to channel flows, and the computed results are discussed in comparison with the direct numerical simulation and the Smagorinsky–Van Driest model. Special attention is paid to the dependence of the results on the Reynolds number, the grid resolution, and the choice of a filter function. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287518
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  • 2
    Electronic Resource
    Electronic Resource
    Statistical analysis of turbulent-transport suppression based on the magnetohydrodynamic approximation with electric-field effects incorporated (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2902-2911 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Suppression mechanism of turbulent thermal-energy transport is studied using the statistical method based on an extended magnetohydrodynamic (MHD) approximation. The one-fluid MHD system of equations is supplemented with effects of electric fields coming from the inhomogeneity of charge density. A Markovianized two-scale method is applied to the resulting system, and the turbulent transport rate of thermal energy is examined. In cylindrical geometry, the transport is shown to be suppressed through the combined effects of the radial electric field and the charge nonuniformity arising from its curvature. This finding is discussed in light of the formation of transport barriers observed in tokamak's high-confinement modes and is confirmed to be consistent with observational results. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873012
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetohydrodynamic mechanisms of electric-field transport suppression and plasma-rotation generation, with special reference to tokamak's reversed-shear confinement (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3194-3206 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A magnetohydrodynamic analysis is made of the mechanisms of electric-field transport suppression and plasma-flow generation in the context of tokamak's reversed-shear (RS) confinement. The turbulent transport of heat is shown to be suppressed through the combined effect of radial electric field and charge inhomogeneity. The similarity is pointed out between the internal transport barrier in RS modes and the edge counterpart in high-confinement modes. A concave electric-current profile is shown to be a cause of the global plasma rotation, and the latter contributes to the occurrence of a negative radial electric field that plays a key role in the former suppression mechanism. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873559
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  • 4
    Electronic Resource
    Electronic Resource
    Compressibility and rotation effects on transport suppression in magnetohydrodynamic turbulence (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 889-900 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Compressibility and rotation effects on turbulent transports in magnetohydrodynamic (MHD) flows under arbitrary mean field are investigated using a Markovianized two-scale statistical approach. Some new aspects of MHD turbulence are pointed out in close relation to plasma compressibility. Special attention is paid to the turbulent electromotive force, which plays a central role in the generation of magnetic and velocity fluctuations. In addition to plasma rotation, the interaction between compressibility and magnetic fields is shown to bring a few factors suppressing MHD fluctuations and, eventually, density and temperature transports, even in the presence of steep mean density and temperature gradients. This finding is discussed in the context of the turbulence-suppression mechanism in the tokamak's high-confinement modes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871792
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  • 5
    Electronic Resource
    Electronic Resource
    Collimation mechanism of magnetohydrodynamic jets based on helicity and cross-helicity dynamos, with reference to astronomical jets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2646-2653 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A collimation mechanism of magnetohydrodynamic jets is sought on the basis of the turbulent-dynamo theory within the framework of fluid incompressibility. The momentum diffusion giving rise to the broadening of the jets is suppressed through the cross-helicity effect, whereas the diffusion of the magnetic field is hampered owing to the helicity effect. These two effects lead to the collimation of electrically conducting jets in the presence of turbulent fluctuations of the velocity and magnetic field. The relevance to collimated astronomical jets is discussed with the reservation about effects of fluid compressibility. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874106
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  • 6
    Electronic Resource
    Electronic Resource
    Turbulent magnetohydrodynamic dynamo based on alpha and cross-helicity effects, with special reference to geomagnetic fields (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4586-4596 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetohydrodynamic (MHD) state in a wide-gap spherical shell mimicking the earth's outer core is examined with resort to the mean-field or turbulent-dynamo theory. In the dynamo, the induced mean magnetic field is in a quasi-force-free state under a large alpha effect. The saturation level of the field is determined through the alignment with the mean velocity under a cross-helicity effect. On this basis, the following characteristics of the induced field are elucidated: The energy of the magnetic field becomes much larger than the kinetic one of the fluid motion driven by buoyancy force; the Lorentz force coming from the field remains less dominant than the buoyancy force; the toroidal component of the field is larger than the poloidal one. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873746
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  • 7
    Electronic Resource
    Electronic Resource
    Stationary large-scale magnetic fields generated by turbulent motion in a spherical region (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3604-3613 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stationary large-scale magnetic fields generated by an electrically conducting fluid in a spherical region are examined analytically, using the concept of the turbulent dynamo based on helicity and cross-helicity effects. Under this concept, the toroidal magnetic field is induced through the combination of a rotational motion and the turbulent cross-helicity effect. This field generates the poloidal one through the turbulent residual-helicity (alpha) effect. A new magnetic-field generation mechanism in the vicinity of the poles is also described. These findings are discussed in the context of the dimension of the convection part of a stellar object. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871952
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  • 8
    Electronic Resource
    Electronic Resource
    Derivation of a model Reynolds-stress transport equation using the renormalization of the eddy-viscosity-type representation (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 707-715 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Terms in an asymptotic expansion for the Reynolds stress with the eddy-viscosity approximation as the leading part are summed up partially but infinitely. This renormalization procedure leads to a model Reynolds-stress transport equation. The equation is shown to retain the important structures of the counterparts in the conventional second-order modeling that are widely used for the study of engineering turbulence. The present method clarifies the mathematical properties of each term in the conventional models, specifically, the prominent difference between the roles of the slow and rapid terms in the pressure–strain correlation function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858654
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  • 9
    Electronic Resource
    Electronic Resource
    A nonequilibrium representation of the turbulent viscosity based on a two-scale turbulence theory (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3302-3304 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonequilibrium expression of the turbulent viscosity in the Reynolds stress is proposed with the aid of the results from a two-scale direct-interaction approximation. The usual turbulent-viscosity model based on the turbulent kinetic energy K and its dissipation rate ε is extended to include their nonequilibrium effects DK/Dt and Dε/Dt (D/Dt is the Lagrange derivative based on the mean velocity). The validity of the proposed model is confirmed through the test in homogeneous shear turbulence that is in a state of nonequilibrium in time. The relationship with the similar model presented by Taulbee [Phys. Fluids A 4, 2555 (1992)] is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858690
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  • 10
    Electronic Resource
    Electronic Resource
    Eddy-viscosity-type subgrid-scale model with a variable Smagorinsky coefficient and its relationship with the one-equation model in large eddy simulation (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2007-2009 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Subgrid-scale (SGS) modeling in the large eddy simulation of incompressible turbulence is revisited with special emphasis on the equation for the SGS kinetic energy. Using this equation, the Smagorinsky model can be converted to a SGS model with the effects of advection and transport incorporated into the Smagorinsky coefficient. The relationship with the one-equation SGS model that directly uses the equation for the SGS kinetic energy is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857934
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