Numerical stability of the mixture drift flux equations

Drift flux models are commonly used to describe two-phase flow systems when explicit representation of the relative phase motion is not required. In these models, relative phase velocity is typically described by flow-regime-dependent, semi-empirical models. Although they are a somewhat simple description of the two-phase conditions that might be expected in nuclear power systems, drift flux models can still be expected to give reasonable results in a significant range of operating conditions and can be useful in incorporating thermal-hydraulic feedback into steady-state and transient neutronics calculations. In this paper, we examine the numerical stability associated with the finite difference solution of the mixture drift flux equations. We assume a standard semi-implicit discretization on a staggered spatial mesh, where the drift flux terms are evaluated purely explicitly.