Experiment on erosion of hollow cylinders by cavitating jet of hydraulic oil

Abstract

Erosion of non-collision surfaces by cavitating oil jets was investigated experimentally using hollow cylindrical specimens. The stainless steel chamber with an inner diameter of 170 mm was utilized, including the nozzle of 1 mm in diameter and 4 mm in length. The aluminum specimens with a length of 20 mm, an outer diameter of 20 mm, and inner diameters of 3, 5, and 7 mm were prepared. The test fluid was hydraulic oil with a viscosity grade of 32 and the temperature was maintained at 40°C. The upstream and downstream absolute pressure were set at 10.1 MPa and 0.2 MPa, respectively, so that the cavitation number defined by the ratio of the downstream pressure to the upstream pressure was 0.02. The stand-off distance was varied from 10 to 25 mm in increments of 2.5 mm. The specimens were observed at 1 hour intervals and the exposure time was up to 8 hours. The specimens were cut in half by a precision machine tool after the completion of the experiments to observe and examine the eroded surfaces. The specimens were partially eroded on their inner walls close to the downstream ends. The eroded region shifted slightly upstream as the stand-off distance increased. The erosion was less pronounced for specimens with a large inner diameter.