2-FLUID MODEL OF WAVY SEPARATED 2-PHASE FLOW

The objective of this study is to develop a local two-fluid model for the separated two-phase flow pattern, usually referred to as stratifie d flow, Previous models considered the stratified how pattern as a sup erimposition of two single-phase hows. However, this assumption is val id for the cases in which the amplitude interfacial waves are small co mpared to the liquid thickness. In this paper, we propose a complement ary approach for the case of thin films in comparison to the wavy regi on. In this case, a local two-fluid model accounting for the distribut ion of the two phases is necessary. The paper is based on one such loc al model of the separated two-phase flow pattern. Since the model does not predict the shape of the gas-liquid interface, we assume it is kn own a priori. The model accounts for the wavy surface and the interfac ial transfer of momentum; this transfer can be induced both by pressur e and viscous stress distributions along the wavy gas-liquid interface . In the first part the mathematical development to establish the loca l two-fluid model of separated two-phase how is presented. In the seco nd part, the adequacy and advantages of simplifying the wave field by assuming a monochromatic dominant wave are considered. The closure con ditions for the model are also presented. Interfacial terms of momentu m transfer are shown to account for both the shape of the gas-liquid i nterface and for the distributions of stresses over it. The key featur e of the two-fluid model lies in the transfer of momentum at the wavy gas-liquid surface. The transfer of momentum at the gas-liquid interfa ce raises two issues: the first is the deformation of the gas-liquid i nterface, the second is the distribution of the stresses over a wavy b oundary (pressure and viscous stresses). The generation of waves, thei r deformation and propagation are beyond the scope of this work. Iin t he second part of this paper, our goal is to adequately predict the ef fect of the distribution of the stresses over a wavy boundary for a gi ven shape. In particular, the weight of the pressure term in the trans fer of interfacial momentum is estimated. (C) 1997 Elsevier Science Lt d.