NUMERICAL SIMULATION OF THE FORMATION AND REATACHMENT LENGTH OF WATER JET FOR DIFFERENT ORIFICE GEOMETRIES

The flow through water jet orifices is important because of its effects on the jet characteristics (jet break-up length and momentum distribution). In this paper, Computational Fluid Dynamics (CFD) simulation was performed to improve the understanding of water jet formation and fluid flow process through the orifice under high injection pressures. In particular, water jet formation and reattachment length in sharp edged diamond orifices were studied. The investigation used a two dimensional, axisimetric, two-phase, transient-state model of orifice flow to observe the effects of capillary length and diameter on the jet break-up length. The injection pressure was varied from 10 MPa to 700 MPa. Results are presented for two standard diamond orifice types. Type-1 orifice, which is used for pure water jet cutting, produced a constricted water jet with no apparent cavitations during the jet formation at typical water jet cutting pressures. On the other hand, flow in type-2 orifice (a typical orifice used for abrasive water jet cutting), at similar injection pressures, quickly reattaches to the wall of the orifice.