Numerical Simulation And Experimental Research On Simplified Flow Field Of Cavitation Jet Cleaner

The cavitation cleaning is a cleaning technology including cavitation and water jet technology.Its advantages are high safety,suitable for long-distance pipeline cleaning and environmental protection,pipeline fouling will be deformed,denuded and washed under the repeated action of strong pressure and strong jet generated by cavitation jet cleaner during the cleaning process.In this paper,simplified model of the cavitation jet cleaner is taken as the research object,the collapse process of a single cavitation bubble driven by high pressure is analyzed.The flow field characteristics for simplified model of the cleaner are analyzed in detail.The details are as follows:Based on VOF model for capturing vapor-liquid interface,considering mass transfer and thermodynamic effects,the phase transition model is used to simulate the collapse and rebound processes of a single cavitation bubble.By comparing the results of the collapse processes without phase transition and with phase transition,the morphological of a single cavitation bubble at different times and the characteristics of pressure distribution and temperature distribution in the flow field are analyzed.The results show that the maximum pressure in the flow field is 1105 MPa during collapse without considering the phase transition.Considering the phase transition,the maximum pressure in the flow field reaches 238 MPa,the maximum temperature in the flow field is 2416 K,the single cavitation bubble bounce back to about 21%of the initial radius,the phase transition model can simulate the collapse and springback process of a single cavitation bubble.A simplified two-dimensional symmetrical flow field model of the cavitation jet cleaner is established and is solved by transient numerical method.UDF technology is used to set variable pressure boundary condition,the influence of inlet pressure on stable cavitation in simplified flow field is analyzed.The results show that when the inlet pressure ranges from 0.1 MPa to 0.6 MPa,the vapor volume fraction is distributed in the throat between the cleaner and pipeline.When the inlet pressure is above 0.7 MPa,local cavitation occurs downstream of the cleaner.Based on overlapping grid technology,the pressure distribution,velocity distribution and vapor volume fraction of the simplified flow field at different speeds of the cleaner are analyzed.The results show that when speed of the cleaner is less than 0.191 m/s,with the increase of speed of the cleaner,the eddy current effects in the flow field change strongly,and the flow field characteristics change irregularly,when speed of the cleaner is larger than 0.191 m/s and stable at 0.277 m/s,the viscous and shear forces near the throat between the cleaner and the pipeline are balanced,the eddy current effects change weaker,the characteristics of flow field tend to be stable.The cleaning effect of cavitation jet is tested by jet impact test,visual test and pressure distribution test.In the study,surface morphology and roughness of the impact specimens are measured under different working pressures,the variation of the cavitation length and the pressure at different locations in the flow fluid are tested.The results show that with the increase of working pressure,the size of micro-pits and the surface roughness of the specimens increase gradually after the impact test,the cavitation area of the cavitation cleaner expands,and the negative pressure effect is enhanced.