LDA measurements of local velocities inside the gas phase in horizontal stratified/atomization two-phase flow

New data on local axial velocities, inside the gas phase in horizontal stratified/atomization air-water pipe flow are reported. Mean local velocities, RMS values and other statistical information have been obtained by analyzing the instantaneous velocity records. From the velocity profiles a secondary flow pattern is inferred with an upward motion at the pipe wall and a downward motion at the vertical pipe centerline. The new measurements are assessed in connection with already reported data of liquid layer characteristics and wall shear stress, obtained under the same flow conditions. The velocity spectra clearly exhibit the influence of the large waves on the gas phase, near the gas-liquid interface; they also suggest that this influence extends up to the top wall of the pipe, probably through the secondary motion inside the gas phase. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.