| Summary: | Evolution of thin liquid films sheared by co-current gas stream in a vertical 11.7 mm pipe is studied experimentally using BBLIF technique. The main goal is to investigate the transition of wave patterns due to increase in the gas stream velocity, VG, from 0 to 24 m/s. Apart from relatively weak quantitative changes in the characteristics of the primary
waves, replacement of capillary precursor by slow secondary waves is found. The transition is indentified in the range of VG = 8 - 16 m/s for all liquid flow rates. It is observed that the appearing secondary waves may be the main reason of the decay of the capillary precursor. The experimental results are compared to prediction of evolutionary theoretical model, showing qualitative agreement on secondary waves generation, but with no agreement on precursor's disappearance. Introducing artificial perturbations mimicking the action of turbulent pulsations in the gas phase is recommended to improve the model.
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