CIRCUMFERENTIAL NONUNIFORMITY OF WAVES ON LIQUID FILM IN ANNULAR FLOW WITHOUT LIQUID ENTRAINMENT

The wavy structure of liquid film in downward annular flow without liquid entrainment is studied. Temporal evolution of instantaneous distributions of local film thickness over longitudinal and circumferential coordinates is studied using high-speed laser-induced fluorescence technique. Wavy structure in such flow consists of fast long-living primary waves and slow short-living secondary waves that are generated at the back slopes of primary waves. An automatic algorithm of identification of characteristic lines of primary waves is applied to data obtained in a number of circumferential positions. Contours of waves in each time frame are identified to obtain temporal evolution of the shape of each wave in longitudinal and circumferential coordinates. Circumferential size of primary waves is estimated based on frequency of different kinds of waves. It is shown that variation of primary waves' height along circumferential coordinate is most likely caused by absorption and generation of secondary waves.