Interacting convection zones

3D Numerical simulations of convection zones separated by a stable layer (a ccording to the Schwarzschild criterion) are presented. The compressible ca se is considered. We make use of idealized microphysics closely related to polytropes. Decreasing the importance of the separating stable layer by dim inishing its vertical extent in a series of models we investigate how the t wo convection zones merge into one. In our parameter range it is the upper zone which increases in size and ultimately squeezes the lower convection z one more or less out of existence. Properties of various fluxes and other p hysical quantities are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.