Two-zone analysis of wavy two-phase flow using micro-particle image velocimetry (micro-PIV)

Micro-scale particle imaging velocimetry (micro-PIV) has been applied to 20 two-phase air–water flows in the wavy regime and near the wavy/annular regime transition. Velocity profiles and fluctuation statistics have been calculated based on the particle image pairs produced, which were divided into base film and wave zones. A linear velocity profile is seen within the base film that extends farther from the wall than in turbulent single-phase channel flow. Axial velocities and fluctuation statistics are observed to be significantly higher in waves. An increase in the axial fluctuation intensity that stems from the difference between waves and base film is observed with increasing gas flow, which may be indicative of a regime transition. The possible sources of the fluctuations, including turbulence and the variable shear experienced by the film, are also outlined