Laminar–turbulent transition and wave–turbulence interaction in stratified horizontal two-phase pipe flow

Abstract

Stratified cocurrent flow of air and water was studied experimentally in a 5 cm diameter horizontal pipe. The velocity in the liquid phase was measured using planar particle image velocimetry, and the instantaneous interfacial profile was recorded using a separate camera. The resulting velocity fields extended from the pipe wall to the wavy interface. The principal aims of the study were to investigate the laminar–turbulent transition of the liquid phase in stratified gas–liquid flow, and to explore the interaction between the transition process and the interfacial waves. The boundaries of transition were determined in both the smooth and the wavy region. The occurrence of waves had the effect of increasing the Reynolds numbers at the end of transition. On the other hand, the transition to turbulence caused a change from the ‘2D small-amplitude’ to the ‘3D small-amplitude’ wave pattern, which were seen to correspond to the capillary–gravity and gravity–capillary solutions of the dispersion relationship respectively. In light of this, the flowmap of the wavy region was recast into Weber number–Froude number coordinates, which provided a physical interpretation of the interaction between the developing turbulence and the changing wave patterns.