Core Annular Two Phase Flow in Gently Curved Surfaces

S. Pushpavanam

In this talk, the hydrodynamic features of a two phase core annular flow through a curved channel will be highlighted. A simplified case of a concentric fluid –fluid interface and a gentle axial curvature is considered. This allows us to seek an analytical solution in the form of a regular asymptotic expansion to the first order. Two key features of the flow will be discussed; the secondary circulations and the redistribution of the axial velocity.
The viscous coupling of the two fluids at the interface results in a range of circulation patterns. In addition to the well known Dean vortices observed in single phase flows we demonstrate the presence of additional flow features such as sandwich vortices and dominated vortices. Their presence is indicative of a conflict in the flow directions at the interface which nearly always results in one of the fluids dictating the flow within  the other.

A similar rich behavior is found in the axial velocity distribution. The competing effects of the axial curvature are identified with the aid of previous results on single phase flows. These are given a physical interpretation and termed the geometric and inertial effects. These competing mechanisms within each fluid can result in the axial velocity being greater in either the inner or outer half of the channel.

The circulation pattern has a non trivial dependence on the physical parameter space.  Analytical conditions are used to divide the parameter space into different regions where the flow behavior is different. This provides a physical insight into the flow behavior of the system.