Experimental investigation on dynamic characteristics of ventilation bubbles on the surface of a vertical moving body

The problem of jet in cross flow has been studied for many decades. However, the investigation on gas jet in liquid cross flow is still rare. In addition, although ventilated cavity has been widely studied in ship drag reduction where the gas jet is injected into a cross flow vertically, the investigation on the dynamic behaviors of gas jet injected into cross flow horizontally is scarce. In this paper, an experimental device was designed to study dynamic characteristics of the ventilation bubbles injected from a vertical moving body. The bubble dynamic behaviors were captured by a high speed camera. Based on the experimental system, a series of experiments of the air exhaust process from a vertical moving body is studied under different motion states of the vertical moving body and different initial pressure ratio. The air accumulation effect and low pressure region on front of the ventilation holes causing the front of the ventilation bubble moves toward the head. Also, due to the Coandă effect and pressure difference the closure mode of re-entrant jet is presented. In addition, three types of flow patterns of the ventilation bubble were discovered. •The unsteady bubble dynamic behaviours near the venting holes are observed and analyzed.•Morphological transformation and position of the re-entrant jet have been studied.•Pressure evolutions inside the air chamber with different conditions are presented.•Three flow patterns of interaction between adjacent bubbles have been discovered.