A 2-PHASE FLOW MODEL OF THE RAYLEIGH-TAYLOR MIXING ZONE

The Rayleigh-Taylor instability of an interface separating fluids of d istinct density is driven by an acceleration across the interface. Low order statistical moments of fluctuating fluid quantities characteriz e the hydrodynamics of the mixing zone. A new model is proposed for th e momentum coupling between the two phases. This model is validated ag ainst computational data for compressible flows, including flows near the incompressible limit. Our main result is a zero parameter first or der closure for ensemble averaged two phase flow equations. We do not, however, fully solve the closure problem, as the equations we derive are missing an (internal) boundary condition along any surface for whi ch either phase goes to zero volume fraction. In this sense, the closu re problem is reduced from a volume to a surface condition, rather tha n being solved completely. We compare two formulations of the statisti cal moments, one based on two phase flow and the other on turbulence m odels. These formulations describe different aspects of the mixing pro cess. For the problem considered, the two phase flow moments appear to be preferable, in that they subsume the turbulence moments but not co nversely. (C) 1996 American Institute of Physics.