Angular momentum transport in convectively unstable shear flows

Abstract

Angular momentum transport owing to hydrodynamic turbulent convection is studied using local three dimensional numerical simulations employing the shearing box approximation. We determine the turbulent viscosity from non-rotating runs over a range of values of the shear parameter and use a simple analytical model in order to extract the non-diffusive contribution (Lambda-effect) to the stress in runs where rotation is included. Our results suggest that the turbulent viscosity is of the order of the mixing length estimate and weakly affected by rotation. The Lambda-effect is non-zero and a factor of 2-4 smaller than the turbulent viscosity in the slow rotation regime. We demonstrate that for Keplerian shear, the angular momentum transport can change sign and be outward when the rotation period is greater than the turnover time, i.e. when the Coriolis number is below unity. This result seems to be relatively independent of the value of the Rayleigh number.

10 pages, 12 figures, published version. Version with higher resolution figures can be found at http://www.helsinki.fi/~kapyla/publ.html

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• Reynolds stress and heat flux in spherical shell convection
• Confirmation of bistable stellar differential rotation profiles
• Oscillatory large-scale dynamos from Cartesian convection simulations
• Turbulent viscosity and effective magnetic Prandtl number from simulations of isotropically forced turbulence
• Magnetic and rotational quenching of the $\Lambda$ effect
• Effects of small-scale dynamo and compressibility on the $\Lambda$ effect
• Excitation of spiral density waves by convection in accretion discs