where 2S is the viscosity computed by the Smagorinsky formulation (Smagorinsky, 1963), α is a constant in the range 0.01-0.5 and A denotes the area of the current element. A value of α = 0.1 was used keeping in mind the fine resolution of the mesh. Similar to the eddy viscosity, turbulent diffusion in the transport equations (equation 4 in the paper) represents all those processes that can not ...

Aims. We provide a consistent theory of the tachocline confinement (or anisotropic momentum transport) within an hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant...

Turbulence in compressible plasma plays a key role inmany areas of astrophysics and engineering. The extreme plasma parameters in these environments, e.g. highReynolds numbers, supersonic and super-Alfvenic flows, however,make direct numerical simulations computationally intractable even for the simplest treatment—magnetohydrodynamics (MHD). To overcome this problemone can use subgrid-scale (SG...

A new model to calculate heat eddy diffusivity in separating and reattaching flows based on modification of constant Prt is proposed. This modification is made using an empirical correlation between maximum Nusselt number and entrance Reynolds number. The model includes both the simplicity of Prt=0.9 assumption and the accuracy of two-equation heat-transfer models. Furthermore, an appropriate l...

For the purpose of studying the spectral properties of energy transfer between large and small scales in high-Reynolds-number turbulence, we measure the longitudinal subgrid-scale (SGS) dissipation spectrum, defined as the co-spectrum of the SGS stress and filtered strain-rate tensors. An array of four closely spaced X-wire probes enables us to approximate a two-dimensional box filter by averag...

The dependence of intermittent inertial properties on ultraviolet eddy viscosity closures is examined within the framework of shellmodels of turbulent flows. Inertial intermittent exponents turn out to be fairly independent on the way energy is dissipated at small scales.

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Two approaches for closing the turbulence subgrid-scale stress tensor in terms of matrix exponentials are introduced and compared. The first approach is based on a formal solution of the stress transport equation in which the production terms can be integrated exactly in terms of matrix exponentials. This formal solution of the subgrid-scale stress transport equation is shown to be useful to ex...