Some peculiar features of hydrodynamic instability development.

We discuss the results of experiments that illustrate some features of a turbulent mixing zone (TMZ) structure at a gas-liquid interface (Rayleigh-Taylor instability) and at a gas-gas interface accelerated by shock waves (Richtmyer-Meshkov instability). The important feature is the existence of a heavier substance concentration (density) jump at the interface between the heavy medium and the TMZ. It is found that the existence of this jump is a generic feature of any developed TMZ and is the necessary condition for its continuous development. In the case of a gas-liquid interface, the stable existence of this jump is connected with the stability of the cupola of gas bubbles penetrating into the liquid in a TMZ. The important feature of the development of interface instability accelerated by an unsteady shock is the decaying ability (up to full suppression) of the interface instability in the case when a decaying wave passes through the interface in the direction from light gas to heavy gas.