Revisiting the mechanism responsible for the stratified-slug transition in two-phase flows

Linear stability analysis is extensively used for predicting the transition between stratified and slug flow. In the present work, a one-dimensional two-fluid flow is linearly perturbed to evaluate the behavior of the dispersion curves through parameters such as the maximum wave growth rate (${\omega }_{I,max}$), the fastest-growing wave ($k_{max}$) and the wave that makes the problem permanently stable ($k_c$) as a function of the gas and liquid superficial velocities. The novelty of this article relies upon coupling the analysis of the behavior of transition-related parameters to the physical effects that are responsible for stabilizing and destabilizing the flow interface. The coupling of the transition analysis with the physical parameters showed potential as a reliable way of explaining the obtained transition behavior. By doing this, the stabilizing effects of gravity and surface tension are found to be invariable to the superficial velocities of the phases. On the other hand, the destabilizing effect of inertia increased with phase superficial velocities, while the shear stress increases with the liquid superficial velocity and shows a non-monotonic behavior with the gas superficial velocity. Although the overall trend of ${\omega }_{I,max}$, $k_{max}$ and $k_c$ was to increase with the superficial velocities of the phases, they were directly affected by the shear stress behavior, also showing a non-monotonic trend.