부산대학교 도서관

We study the dynamics associated with the extension of turbulent convectivemotions from a convection zone (CZ) into a stable region (RZ) that lies belowthe latter. For that purpose, we have run a series of three-dimensional directnumerical simulations solving the Navier-Stokes equations under the Boussinesqapproximation in a spherical shell geometry. We observe that the overshootingof the turbulent motions into the stably stratified region depends on threedifferent parameters: the relative stability of the RZ, the transition widthbetween the two, and the intensity of the turbulence. In the cases studied,these motions manage to partially alter the thermal stratification and inducethermal mixing, but not so efficiently as to extend the nominal CZ further downinto the stable region. We find that the kinetic energy below the convectionzone can be modeled by a half-Gaussian profile whose amplitude and width can bepredicted a priori for all of our simulations. We examine different dynamicallengthscales related to the depth of the extension of the motions into the RZ,and we find that they all scale remarkably well with a lengthscale that stemsfrom a simple energetic argument. We discuss the implications of our findingsfor 1D stellar evolution calculations.