Numerical Simulation of the Formation of Constricted Waterjets in Hydroentangling Nozzles: Effects of Nozzle Geometry

The role of nozzle geometry on the formation of constricted waterjets, waterjets that are detached from the wall throughout the nozzle, is considered in this paper. Such waterjets have found applications in various industries, including nonwoven processing. Due to the very small time and length scales involved in high-speed flow through micro-nozzles, experimental observation of the jet formation is cumbersome if not impossible. Computer simulation, on the other hand, can improve our understanding of the waterjet formation process under such conditions. In this paper, we report on flow simulations of water through sharp-edge cone-capillary nozzles having a diameter of 128 μm at different Reynolds numbers. Unsteady-state laminar two-phase flow is considered in axisymmetric nozzles with different capillary lengths. Our simulations show the separation of the flow from the nozzle wall as it enters the orifice. Simulations have also revealed that flow reattachment occurs in cases where the nozzle capillary length is longer than a critical length. For sharpedge nozzles operating at high Reynolds numbers, the critical capillary length is found to be about 70% of the nozzle diameter. Nozzles with a capillary length less than the above critical length produce a constricted waterjet with no apparent cavitation during the jet formation.