Behavior and erosion capacity of an inclined plunging JET
Type:
Presented during:
CEDA Dredging Days 2024
Authors:
R.M. Keij, A.J. Nobel and A.M. Talmon
Abstract
This study provides insights into the behaviour and erosion capacity of inclined plunging jets. These jets are commonly used to accelerate the removal of sand adhering on the side walls of a hopper. Experimental tests were conducted to replicate an inclined jet traveling through air and then through water on a 1:2 scale. The velocity was determined using the stagnation pressure and water concentration. These were measured using a pitot tube and conductivity sensors respectively. Four setups under a 40-degree angle compared aspects of the water jetting system in a hopper. The first setup involved 75 nozzle diameters of straight pipe upstream of the nozzle, while the second was identical except for an inclined flap covering the nozzle. The third setup included an S-bend 40 nozzle diameters upstream of the nozzle, and the fourth had the S-bend directly before the nozzle, resembling the prototype. In air the jet showed a negligible decrease in velocity but a significant decrease in water concentration. The S-bend directly before the nozzle and the flap displayed the worst jet coherence, as these accelerated the mixing of the jet with air. The submerged jet production remained constant up to 0.5 m of water layer, possibly due to the jet shearing over the sand bed instead of burrowing, increasing jet production. Or it could be a slower velocity decrease due to the air entrained into the jet obstructing the stagnant water from mixing into the jet and decreasing its velocity due to determined by measuring the mass decrease of a submerged sand container. When adjusting for decreased mixture density the production was still 2 times lower, possibly because of poor jet coherence due to entrained air.
Keywords: Hopper, plunging, jet, erosion, submerged