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We have reported recently on a comparative study of boundary conditions in simulations of compressible convection, and how these determine certain aspects of the solutions (M. Hossain and D. J. Mullan, ApJ 416, 733 [1993]). In that work, the simulations were confined to a layer which was convectively unstable throughout its extent. Since the medium is compressible, the solutions contain not only convective modes but also acoustic components. The results indicated that the relative contribution of the acoustic components to the overall flows can vary significantly depending on which boundary conditions are applied. We are now extending the work to investigate how the addition of convectively stable layers below and/or above the unstable layer will affect the solutions. As far as the convective modes are concerned, it is already known that the presence of an overlying stable layer may increase or decrease the critical Rayleigh number depending on the degree of stability (V. Savolainen et al. Phys. Fluids A4, 626 [1992]). Here, we use simulations to investigate how the acoustic components are affected. To avoid numerical difficulties, both the initial states and the transport coefficients are taken as analytic functions of depth. Preliminary results from such attempts will be reported.
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\noindent This work has been supported by NASA grant NAGW-2456.
