Rock-breaking Mechanism And Parametric Influences Of Abrasive Cavitation Jet

It is constantly pursued to increase the rock-breaking efficiency and reduce the rig time in drilling engineering.Abrasive particles are added into cavitation jet to form the abrasive cavitation jet,which utilizes the cavitation bubble erosion and the impact of abrasive particles to break rocks.It is expected that abrasive cavitation jet can greatly improve the rock-breaking efficiency.In the abrasive cavitation jet,the crucial issues include the synergistic effect between cavitation bubbles and abrasive particles,the characteristics of jet cavitation cloud,the rock failure characteristics under abrasive cavitation effect,and the influences of relevant parameters on the jet erosion ability.Present doctoral dissertation conducts numerical simulation and experiments to investigate the rock-breaking mechanism and parametric influences of abrasive cavitation jet.The dynamics of the cavitation bubble and the synergistic effect between the cavitation bubble and the abrasive particle are numerically investigated using Lattice Boltzmann method.As cavitation nuclei,abrasive particles reduce the requirement of cavitation inception and enhance the number of cavitation bubbles,thus strengthening the jet cavitation intensity.The expansion of cavitation bubbles can accelerate abrasive particles.The accelerated particles lead to additional damage when they impact on material.The characteristics of jet cavitation cloud are investigated by the visualization experiment.The cavitation cloud in cavitation jet is periodic.One period is composed of inception,development,shedding,and collapse processes.With the particle mass concentration increasing from 0 to 3.05 wt%,the periodicity of cavitation cloud gradually disappears while its area increases by at most 457.11%.The modes of cavitation cloud are symmetrically distributed around the jet centerline.The second mode represents the principal dynamic structure of cavitation cloud.Under the same mass concentration,the promotion effect of abrasive particles on cavitation decreases as the particle diameter increases from 0.075 to 0.425 mm.Compared with cavitation jet,the acoustical power of cavitation noise is increased by at most 113.24% in abrasive cavitation jet.Abrasive ultrasonic cavitation experiment and erosion test of abrasive cavitation jet are performed.The rock failure characteristics under abrasive cavitation effect and the parameter influences(standoff distance,erosion time,mass concentration of abrasive particles,erosion material)on jet erosion ability are clarified.Abrasive cavitation effect destroys the cementation structure of sandstone and shale.Erosion pits are formed after mineral particles are removed.Numerous pores and micro-fractures are produced.The erosion pits of shale grow along the bedding direction.The granite minerals are peeled off along crystal plane or spit,leaving erosion pits with sharp edges.Pores are not developed on granite while inter-granular fractures are well developed.The erosion ability of abrasive cavitation jet increases with mass concentration of abrasive particles.The size of central hole decreases,while the cavitation damage first increases then decreases,with increasing standoff distance.Jet reaches the maximum cavitation intensity at a non-dimensional standoff distance of 100.The sequence of mass loss is sandstone>shale>granite while that of surface roughness is sandstone>granite>shale.Abrasive cavitation jet has the best erosion performance on sandstone,followed by shale and granite.Abrasive cavitation jet increases the volumes of central hole and annular cavitation zone for sandstone;the mass loss of shale mostly comes from the central hole eroded by abrasive jet;cavitation erosion pits on granite are individually distributed.Compared with cavitation jet,the mass losses of sandstone,shale,and granite eroded by abrasive cavitation jet are increased by at most 86.96%,1348.28%,and 432.41%.Present work reveals the rock-breaking mechanism and parametric influences of abrasive cavitation jet.It is expected that this work can provide theoretical support for the further development and field application of abrasive cavitation jet technique.