Water jets surrounded by an air film - experimental research
Type:
Presented during:
CEDA Dredging Days 2009 - Dredging Tools for the Future, Rotterdam
Authors:
Vinke F and Talmon AM - Delft University of Technology; Nobel A - Royal Boskalis Westminster The Netherlands
Abstract: The effect of introducing an air film around a water jet is examined in laboratory experiments. The objective is to reduce the friction forces between the water jet and the ambient fluid, making a jet potentially more effective at a larger distance. The test were conducted at a physical scale comparable to dredging practise, contrary to earlier experiments reported in the literature, where small scale jets were tested. During the tests the development of the jet was measured in axial and radial direction. The jet pressure and air discharge were varied, leading to a number of combinations of jet pressures and air discharges. The results showed that also at this scale the development of the water jet is influenced by the air film, although not as much as in the earlier experiments. Governing parameters have been established. Examples are the volume, mass and momentum ratios between the air flow and water flow.
The ratios of the air flow and water flow were not in the same order if the comparison is made between the large and small scale water jets. Relatively less air was added in our tests. A description of the results of a water jet surrounded by an air film with a nozzle diameter of 3 cm is formulated based on the description of a submerged water jet according Rajaratnam (1976) and a description of water jet with an air film with a nozzle diameter of 2 mm according Yahiro and Yoshida (1974).
Keywords: Water jets, air film, experiments