Effects of Area Discontinuity at Nozzle Inlet on the Characteristics of Self-resonating Cavitating Waterjet

The current research on self-resonating cavitating waterjet（SRCW） mainly focuses on the generation mechanism and structure optimization.Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available.In order to further improve the performance of SRCW,effects of area discontinuity（enlargement and contraction） are experimentally investigated using three organ-pipe nozzles.Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects.The results reveal that area enlargement and contraction affect the peak differently,depending on the inlet pressure,nozzle geometry,and standoff distance;while area contraction always improves the amplitude regardless of these factors.At inlet pressures of 10 MPa and 20 MPa,area discontinuity improves the peak at almost all the testing standoff distances,while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa.The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure.Moreover,the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance,depending on the type of area discontinuity and nozzle geometry.A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed.The proposed research provides a new method for effectively enhancing the performance of SRCW.

Flow-visualization and numerical investigation on the optimum design of cavitating jet nozzle

Cavitating jet is widely used in drilling,rock cutting and ocean re source exploitation because of its stro ng erosion ability.The analysis of the relationship between the flow characteristics and the structure of cavitating jet nozzle is critical.Here,we utilized 3 D printed technology and high-speed photography to design visualization experime nts to analyse the impact of the variation of resonator and throat size of the organ-pipe self-resonating cavitating nozzles on the cavitation characteristics through image processing.The velocity field,pressure field and vapor volume fraction injected by the nozzle were taken as the objective functions to study the influence of different structural parameters on the cavitation effect based on FLUENT 19.0 software,and the results were compared with the experimental results.The results show that increasing the length and diameter of the resonator contributes to the occurrence of cavitation and the structure stability of the flow field.However,excessive size affects self-resonant of the nozzle and makes it difficult to form resonance effect.In this study,the optimal values of nozzle throat length and divergent angle are twice the throat diameter and 40°,respectively.This research provides an integrated research method to study the optimization of self-resonating nozzle and cavitating jet characteristics.