A Study of High-Speed Pulsed Water Jets : 2nd Report, Numerical Analysis of Unsteady Flow in Straight Nozzles

Abstract

Pulsed water jets at the velocities of 300m/s to 500m/s produced by piston impact are examined by numerical analysis. Straight nozzles are used with the outlet diameters of 5 and 10mm. The two-step Lax-Wendroff method is employed for the unsteady axisymmetric two-phase flow in the nozzles using a Flux-Corrected Transport algorithm to limit artificial diffusion. After short transition, the flow in the nozzles arrives at a quasi-steady state. In the nozzle outlets, the contract flow and the separation with strong cavitation are formed. The vapor cavities also spread into the water column. Because of the short transition and contract flow, the jet speed of the straight nozzles is higher than that of the taper nozzles with the same nozzle outlet diameter. On the assumption that the flow in the nozzles is steady, the maximum jet speed can be approximated. It is illustrated that the nozzle shape affects the jet speed.