Dual-Orifice Waterjet Predictions and Experiments

Abstract

Listen

Translate article

A simplified dual-orifice circular jet analysis is developed to predict maximum velocity and pressure profile capabilities of waterjets. The analysis is applied to nozzles having total exit diameters of 1.016 mm operating at stagnation pressures of 2.812 MN/m2. These conditions result in flow rates of less than 2.27 × 10-1m3/s of water. Dual-orifice converging nozzles with 2- and 10-deg included convergence angles are analyzed as well as dual-orifice diverging nozzles with 8, 10, and 20-deg included divergence angles. The control-volume form of the conservation of mass and the conservation of momentum equations is applied to the converging dual-jet case. Velocity profiles prior to jet mixing, after Schlichting and Tollmien, are used as profile input to the conservation equations. Profile shapes after Schlichting are used downstream of the jet mixing process. Linear jet diameter growth laws are applied to predict jet diameters before and after the mixing process. The merged jet profiles are calculated downstream of the nozzle at representative stations and compared with a single-orifice jet profile of the same energy input. Diverging dual-orifice jet profiles are generated using the same profile and diameter growth equations as for the converging dual-orifice nozzle jet. Velocity and pressure profiles, generated at representative stations downstream of the nozzle exit, are compared with single-orifice nozzle profiles of the same total energy input. Experimental comparisons are made with 2- and 10-deg included-convergence-angle converging nozzles and with 8, 10, and 20-deg included angle diverging nozzles at 2.812 MN/m2 stagnation pressure. All nozzle shapes consist of a 13-deg converging cone followed by a straight section of length 2.5 exit diameters. A pressure transducer, fixed to the traveling carriage of a lathe and oriented so that the nozzle axis is in line with the transducer axis, is used for profiling studies. A hardened steel shield with a 5.00 × 10-1 mm central hole protects the transducer for the pressure profile studies. These pressure profile measurements are made at the same representative stations as the analytical results. Discussion of the agreement between analytical and experimental results is made with emphasis on limitations of the analytical model, the experimental tests, and on suggested improvements in nozzle design which will bring the analytical predictions and experimental results closer together.