Formation of Large-scale Semi-organized Structures in Turbulent Convection

Israel Science Foundation for Basic Research

C. G. Rossby International Meteorological Institute Foundation

	Large-scale Circulation in Turbulent Convection
	We developed a new mean-field theory of turbulent convection by considering only the small-scale part of spectra as ‘‘turbulence’’ and the large-scale part, as a ‘‘mean flow,’’ which includes both regular and semiorganized motions. The developed theory predicts the convective wind instability in a shear-free turbulent convection. This instability causes formation of large-scale semiorganized fluid motions in the form of cells. The developed theory allows to determine spatial characteristics of these motions, e.g., the minimum size of the growing perturbations and the size of perturbations with the maximum growth rate, and predicts also the existence of the convective shear instability in a sheared turbulent convection. This instability causes formation of large-scale rolls and generation of convective shear waves which have a nonzero hydrodynamic helicity. Increase of shear promotes excitation of the convective shear instability. The obtained results have important implications for to the atmospheric turbulent convection and the laboratory experiments on turbulent convection.
T. Elperin, N. Kleeorin, I. Rogachevskii, and S. Zilitinkevich, Formation of Large-Scale Semiorganized Structures in Turbulent Convection. Physical Review E, 66, 066305(1-15), 2002. PDF: 350 KB T. Elperin, N. Kleeorin, I. Rogachevskii, and S. Zilitinkevich, Tangling turbulence and semi-organized structures in convective boundary layers, Boundary-Layers Meteorology, 119, 449-472, 2006. PDF: 276 KB T. Elperin, I. Golubev, N. Kleeorin, I. Rogachevskii, Large-scale instabilities in a nonrotating turbulent convection, Physics of Fluids, 18, 126601, 2006. PDF: 223 KB

	Hysteresis and Pattern Transitions in Turbulent Convection
	We found the hysteresis phenomenon in turbulent convection in Benard apparatus by varying the temperature difference between the upper and lower plates. The hysteresis loop comprises the one-roll and two-rolls flow patterns while the aspect ratio is kept constant. The developed by us theory of semi-organized structures in turbulent convection is in qualitative agreement with the experimental observations.
A. Eidelman, T. Elperin, N. Kleeorin, A. Markovich, I. Rogachevskii, Hysteresis phenomenon in turbulent convection. Experiments in Fluids, 40, 723-732, 2006. PDF: 783 KB

New Turbulence Closure Model for Numerical Simulations of Stable Atmospheric Boundary Layers

We developed new turbulence closure equations for stable atmospheric boundary layer. The proposed approach distinguishes between the ‘‘Kolmogorov-cascade turbulence’’ and an essentially non-isotropic ‘‘tangling’’ turbulence. These additional anisotropic velocity fluctuations (tangling turbulence) are generated by tangling of the mean-velocity gradients with the Kolmogorov-type turbulence due to the influence of the inertial forces during the life time of large turbulent eddies. The tangling-turbulence closure allows us to determine the Reynolds stresses in anisotropic turbulence, turbulent temperature diffusivity, turbulent Prandtl number as a function of the Richardson number and other parameters.

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