Measurements of gravity and gravity-capillary waves in horizontal gas-liquid pipe flow using PIV in both phases

An experimental study was performed in stratified wavy flow of air and water through a horizontal pipe. The velocity fields in both phases were measured simultaneously using PIV and the interfacial shape was resolved using a profile capturing technique. The objective of the study was to investigate the interfacial characteristics and the velocities of the liquid and gas phases in two wave patterns: '3D small amplitude' and '2D large amplitude' waves. The wave patterns were shown to consist of gravity and gravity-capillary waves, respectively, with substantial differences in the wave characteristics and liquid velocities. Contrary to this, the effect of the waves on the gas velocities was rather similar in both wave regimes, with both wave regimes causing an increase in the velocity fluctuations close to the interface. The current measurements also produced a valuable dataset that can be used to further improve the numerical modeling of the stratified flow pattern.