Published online by Cambridge University Press: 21 April 2006
Experimental results are presented for the instantaneous release of a constant volume of air into water in a long horizontal tube of square cross-section. The tube is closed at both ends and the volume of air is confined at one of the ends before it is released. The resulting motion, after the rapid formation of an air-cavity front, may be divided into three phases: initially the front of the air cavity moves at constant speed, later its speed decreases monotonically, and finally its speed executes a long series of erratic stops and starts before coming entirely to rest. The transition from the first to the second phase is observed to occur when a disturbance due to the tube end overtakes the cavity front. The final phase is dominated by surface-tension effects, complicated by surface contaminants. A simple model of the flow, based on Benjamin's (1968) theory of steady cavity flow and the classical theory of hydraulic jumps, is developed. With correction for surface tension, the model results compare well with the experimental results for the first two phases.