Boundary conditions for a two pressure two-phase flow model

New closures for two pressure two-phase flow in the context of unstable flu id mixing have been proposed recently by the authors. Here we examine the p hysical basis for the models, the nature of the boundary conditions at the edges of the mixing layer, and an algorithm for the numerical solution of t he two-phase flow equations. Physically, the closures describe chunk mix, i n which the flow is dominated by coherent structures of size comparable to the mixing zone thickness. The closed form solution previously introduced f or the incompressible limit is reviewed and extended. Sufficient boundary c onditions for the compressible equations are found from drag and buoyancy l aws proposed by others, with coefficients fit to two sets of independent ex periments. These laws complete the closure of the two-phase flow equations. A postulate of stationary center of mass, previously introduced at a numer ical level, is here related to a weak notion of self similarity and is solv ed analytically for the ratio of the growth rates of the two sides of the m ixing zone in the self similar case. (C) 1999 Elsevier Science B.V. Ail rig hts reserved.