In order to accurately and reliably evaluate the cavitation erosion resistance of materials using a cavitating jet generator, the effects of the hydrodynamic parameters and the nozzle geometry on the erosion process were investigated. Since the behaviour of a high speed submerged cavitating jet is also depending on the working conditions; their influence is also discussed based on the evaluation of cavitation erosion process. The erosion rate was used as an indicator for cavitating jet behaviour. Specimens of commercial-purity copper were subjected to high speed submerged cavitating jets under different initial conditions, for certain time periods. The force generated by jet cavitation is employed to initiate the erosion in surface. The tested specimens were investigated with a digital optical microscope and a profilometer. It was found that erosion becomes more pronounced with decreasing cavitation numbers, as well as with increasing exit jet velocities. The nozzle configuration and hydrodynamic parameters have strong influences on the erosion rate, eroded area and depth of erosion. A comparison between the obtained results explains some of the mechanisms involved in cavitation and erosion processes and their relation to the tested parameters. Mathematical expressions which combine these parameters with the erosion rate are obtained. These parameters are very important in order to control the cavitation as a phenomenon and also to control the performance of the cavitating jet generator.
The influence of the geometrical working parameters on the cavitation erosion process was experimentally investigated by exposing the surfaces of copper samples (as a kind of Face Centred Cubic material (FCC)) to a high speed submerged cavitating jet for various time periods using a cavitating jet generator. The resulting erosion rate and eroded area is discussed in detail. Influences of the nondimensional standoff distance, the non-dimensional aspect ratio and the angle of attack is experimentally determined. The results show that the erosion rate and weight loss are strongly depending on these separately investigated parameters. With this test rig facility and applied hydrodynamic parameters the maximum erosion was found to take place with a non-dimensional standoff distance varying between 42-48 (depending on the nozzle diameter), with a non-dimensional aspect ratio of 11 and with 105° angle of attack. A model to explain the influence of the angle of attack on the erosion rate based on the cavity bubble and target surface interaction is presented. In addition, the obtained results demonstrate that the used small-diameter (0.4 -0.6 mm) water cutting nozzles could be applied for metal machining by cavitation and cavitation cutting with low power consumption and high cutting efficiency.
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