Study On The Characteristics Of Flow Field Inside And Outside The Nozzle Of High Pressure Abrasive Water Jet Under Submerged Conditions

Underwater reef blasting is a commonly used construction method in waterway regulation projects.Huge shock waves and harmful chemical gases in the traditional underwater blasting will cause the destruction of the underwater environment,meanwhile bring threats to the survival of fish as well.Therefore,the development of an environmentally friendly reef-relief technology is of great significance for the future ecological development of inland river navigation.This paper proposes a technical idea that uses abrasive water jets to cutting reefs in an underwater environment.A method combining theoretical analysis and numerical simulation was used to systematically study the flow field distribution inside and outside the abrasive water jet nozzle under submerged conditions.The main research results are as follows:(1)In this paper,two-dimensional mathematical models of pure water jets and abrasive water jets under submerged conditions are established.Through comparative analysis,the flow field distribution of the abrasive jet and water jet are quite similar.The difference is caused by the specific gravity difference leads to the velocity difference during the stages of the jet evolution between solid and liquid phases.(2)For the conical angle of the conical nozzle,the size of the outlet diameter and the length of the cylinder segment,these three important structural parameters were simulated to calculate the submerged abrasive water jet flow field with different nozzle structure sizes.By comparing and analyzing the liquid-solid two-phase velocity changes in the abrasive water jet inside and outside the nozzle,the nozzle structure size was gradually optimized.(3)Simulating and calculating the flow field of submerged abrasive water jet under different conditions of abrasive density,volume concentration and particle size.By comparing the specific changes of the liquid-solid two-phase velocity at the position along the axis and the horizontal section of the abrasive water jet outside the nozzle,the influence of the relevant abrasive properties on the impact velocity of the abrasive water jet is further analyzed.(4)The influence of ambient confining pressure on the changes of the velocity components in the axial and radial directions along the liquid-solid two-phase flow in the abrasive jet was specifically analyzed by calculating the flow field of the abrasive water jet under different water depths.The result shows that the low confining pressure in natural river will cause little influence on the abrasive water jet.(5)The influence of ambient flow velocity on the changes of the velocity components in the axial and radial directions along the liquid-solid two-phase flow in the abrasive jet was analyzed by calculating the flow field of the abrasive water jet under different flow rates.The result shows that the impact of the flow will cause the shifting of the jet,in which the initial area receive relatively few influence.(6)The impinging flow field of the abrasive water jet under different target distances through the simulation.The velocity and dynamic pressure distribution characteristics of liquid-solid two-phase jets were compared and analyzed.Finally,the optimal jet cutting target distance range was determined as 1.5~2.0cm.