Inhomogeneous Multiphase Model for Nonequilibrium Phase Transition and Droplet Dynamics

Abstract

This paper describes the development of an inhomogeneous multiphase model for the prediction of phase transition and nonequilibrium droplet dynamics under transonic flow conditions. The primary application of interest is low pressure steam turbines, where high speeds and complex geometry result in a second phase exhibiting significant droplet size variation, with associated thermal and inertial nonequilibrium relative to the vapor phase. The formulation uses a pressure based, implicit in time, algorithm with finite-volume/finite-element discretization of the conservation equations. For each phase, the velocity, energy state, volume fraction and droplet number are computed. For a two material phase system (water vapor and liquid) a parent and any number of (source based) condensed liquid phases are possible to handle the variety (and complexity) of droplet behavior as found in low pressure steam turbines. The model is tested against experimental data available in the steam turbine community. In particular the influence of inertial nonequilibrium on the phase transition behavior in a steam turbine cascade geometry is examined.