Abstract
This work deals with the processes occurring during the firing of an impact-cumulation water cannon. The breakup of the impulsive water jets produced by such a device is explained in terms of the overpressure of the jets on emergence. Design criteria are identified to produce a fast, coherent jet from such a machine. Pressure histories are shown in the nozzle of the water cannon, together with pressures caused by the impact of a fast moving piston on a water packet. Measurements of the forces exerted by the water jets are given, for jets produced with air or with vacuum in the nozzle. A method for finding the jet head velocity decay is introduced, together with results therefrom. A substantial decay in the jet velocity with distance from the nozzle is noted, for the basic design of water cannon. The pressure distribution in lengths of straight tube attached to the end of the converging region of a nozzle is given, and shows a rapid and exponential fall from the high pressure generated in the nozzle. The impulsive blast noise produced by the firing of the water cannon is quantified and is shown to be eliminated when the piston-water impact is cushioned.