Abstract: To explore the bubble drag reduction of axisymmetric model and understand the characteristics of two-phase flows, the bubble drag reduction with micro-hole array on an axisymmetric model is experimented by using a high speed camera system and a force-measuring system. The experimental results show that the two-phase flow field can be divided into three regions, i.e., stable region, pulsating region and recirculation region, according to the different flow patterns of bubbles in the process of their development. With the increase in ventilation rate, the void fractions in the stable region and the pulsating region increase, and the friction resistance of the model decreases continuously until a saturated ventilation rate is achieved. The flow separation point of recirculation region moves downstream and the tail pressure increases as air entrainment coefficient increases. The flow pattern of the recirculation zone changes at the critical ventilation rate, and the flowing medium is changed from water- gas mixture into gas, which results in a sudden increase in the tail pressure, thereby leading to the sudden increase in the bubble drag reduction. Key

Key words: ordnancescienceandtechnology, axisymmetricmodel, ventilationrate, bubbledragreduction, voidfraction