A systematic study into the cavitation erosion test for marine propeller materials by cavitating jet technique

Abstract

This paper presents an experimental investigation of cavitation erosion on widely used marine propeller materials by the cavitating jet technique as an alternative to cavitation tunnel tests, following the American Society for Testing and Materials (ASTM) standards. The cavitation erosion tests on aluminium samples were, initially, conducted to investigate the effect of stand-off distance and to compare the results with the available data in the literature. The comparative study confirmed that the erosion on the materials has practically the same pattern even if the nozzle diameter and sample size are different for the same cavitation number and at the optimum stand-off distance condition. Following this validation, the samples made of copper-based alloy marine propeller materials, specifically Cu1, Cu3, and Cu4, were tested for the first time in the literature to assess their erosion resistance at various cavitation numbers and test durations by considering various characteristics, such as erosion area, rate and intensity through comprehensive examinations. Among the materials examined, the Cu1, which has the lowest mechanical strength, was found to be the most susceptible to cavitation erosion. Interestingly, despite the Cu4 having the highest mechanical strength, the Cu3 demonstrated better erosion resistance, suggesting that the nickel and copper contents play a crucial role in the material's resistance to erosion. In order to evaluate and assess the cavitation effect more accurately the erosion damage on the material should be examined not only on the surface, but also in the depth. Based on the findings of this study, the cavitating jet technique may be a good alternative to investigate the cavitation erosion characteristics of propeller materials, if a relationship or scaling law between the water jet test technique and full-scale propeller loading, surface conditions, turbulence intensity, and bubble dynamics in operation can be established.