抄録
An abrasive water suspension jet(AWSJ) has a greater capacity for drilling and cutting than a conventional abrasive water injection jet (AWIJ). However, the drilling capability of the AWSJ under submerged condition decreases steeply with the increase of the standoff distance. In order to expand the effective standoff distance of the AWSJ under submerged condition, a sheathed AWSJ nozzle was proposed in the previous paper. In the present paper, observations of the jet issuing from the sheathed nozzle are conducted without addition of abrasive. The injection pressure of the jet is 5 to 10 MPa and the cavitation number is in the range from 0.01 to 0.05. Observations of the flow in the sheath are carried out with a sheath made of transparent acrylic resin pipes. A void filled with vapor is formed in the root part of the sheath. The jet expands fully out to the sheath inner diameter in the region near the sheath exit and a bubbly mixture zone is formed. A cavitation cloud extending from the bubbly mixture zone appears to be continuous near the sheath exit but separates and develops into lumps of cavitation bubbles. The bubbly mixture zone in the sheath fluctuates with time but the frequency of the fluctuation is much smaller than that of the evolution of the lumps of cavitation bubbles outside the sheath.
