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Generation and Propagation of Internal Gravity Waves: Comparison between Two- and Three-Dimensional Models at Low Resolution

Kiraga M., Stępień K., Jahn K.

Acta Astronomica

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2005

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Vol. 55, No. 2

205--217

EN

Dynamics of a convectively unstable layer sandwiched between two stable layers was investigated using direct hydrodynamical simulations in two and three dimensions. Particular attention was paid to the problem of generation and propagation of internal gravity waves (IGW) in a lower stable zone. The results show that convective motions in a 3-D model are significantly less vigorous than in an equivalent 2-D model, resulting in a lower efficiency of IGW generation and a weaker energy flux carried downwards by the waves. The flux obtained in our 3-D models is of the same order as calculated from a simple parametric model based on MLT. However, the comparison of numerical models with different depths of the convective layer indicates that the efficiency of IGW generation increases with the increasing depth whereas the opposite is true in case of parametric model. Extrapolation of this trend to deeper convective zones, existing in solar type stars, suggests that the parametric formulae may severely underestimate the IGW flux generated in the stellar radiative cores. If it is true, IGW existing in real stars will play an important role in transport of angular momentum and trace elements across their internal radiative zones. Due to existence of a rigid lower boundary, the effect of wave reflection occurs in numerical simulations. A method of suppressing the reflected flux is discussed.

2

Direct Numerical Simulations of Penetrative Convection and Generation of Internal Gravity Waves

Kiraga M., Jahn K., Stępień K., Zahn J.-P.

Acta Astronomica

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2003

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Vol. 56, No. 4

321--339

EN

Two-dimensional, direct numerical simulations are used to investigate how thermal convection excites internal gravity waves in the stable layer beneath a convectively unstable zone. The mechanical energy flux carried downwards by the waves strongly depends on the viscosity coefficient. This flux is compared with the energy flux predicted by a simple parametric model of wave generation applied to two models of convection dynamics: one based on the mixing-length treatment and the other on a convective plume model. Numerical simulations always produce substantially larger energy fluxes than the parametric models. This difference may result from shortcomings of the parametric modeling but also from the fact that our simulations are two-dimensional.

3

2D Simulations of Stellar Convection. II. A Study of the Dependence of the Results on Numerical Methods

Kiraga M., Różyczka M., Stępień K., Jahn K., Muthsam H.

Acta Astronomica

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2000

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Vol. 50, No. 1

93--104

EN

Models of a 2-D convectively unstable layer placed between two stable layers are obtained using two independent numerical codes. Penetration ranges and mechanical energy fluxes carried by internal gravity waves are measured for several models with different global parameters. It is shown that both codes produce statistically identical results, which makes them reliable tools for investigations of stellar convection.