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Abstract
High-pressure waterjet (HPWJ) nozzles are used for cutting or for surface treatment such as cleaning, decoating and deburring. The flow within a HPWJ nozzle is compressible and turbulent due to the high water pressure and velocity. Depending on flow velocity and the geometry of the HPWJ nozzle a multiphase flow of liquid and vapor can occur. Outside of the nozzle, a highly complex turbulent waterjet breakup takes place. In order to increase the breakup length of the waterjet, geometric modifications inside the nozzle are required. On the other hand, wear resistance of a nozzle is highly desirable. In this study, the flow inside of a convergent waterjet nozzle was investigated by means of computational fluid dynamics. For the true geometrical model, µ-CT scans of the studied nozzle were used. A reverse engineering process provided the model of the nozzle. The diameter of the orifice was 0.5 mm and the inlet pressure was at 75 MPa. For the modeling of the multiphase flow, the Volume-of-Fluid (VOF) method was applied. Turbulence is also a major influential factor on the primary breakup and therefore the Large-Eddy-Simulation (LES) method was utilized. Since LES method requires good inlet boundary conditions for producing stochastic components of the velocity field, separate Reynolds-Averaged-Navier-Stokes (RANS) simulations for realistic inlet conditions were performed. The studied nozzle had a flow grid, which is located in front of the convergent part of the nozzle. The influence of the flow grid on the waterjet was investigated both in the simulation and in the experiment. To validate the simulations, the flow rates from the experiment were compared with the simulation. High-speed photography provided the spray angle of the waterjet. The results of this study showed that higher turbulence, which was produced by the cross-shaped flow grid, had a stabilizing influence on the primary breakup of the jet.
