Investigations into Dependence Between Cavitation Structures and Cavitation Erosion

Abstract

Experiments within the cavitation erosion incubation period were performed on simple and modified two-dimensional hydrofoils with circular leading edges. A pit-counting method, based on computer-aided image processing, was used for direct measurement of the cavitation erosion by evaluating the damage of the surface. Cavitation phenomenon above hydrofoils at different flow conditions (pressure, water gas content, flow velocity) was observed. A clear relation between characteristics of cavitation structures and cavitation damage was established. A study of influence of gas content in water and flow velocity on the cavitation erosion aggressiveness was performed. There we found a clear influence which shows a drop in aggressiveness of cavitation erosion as the gas content of water is increased. Also a power law was confirmed for velocity influence on cavitation erosive aggressiveness. Due to the extreme length of experiments, many studies tend to perform tests only within the incubation period and the mass loss rate is then predicted by extrapolation. A rotating disc test rig that generates a very aggressive cavitation and pure copper specimens, as erosion sensors, were used to investigate the correlation between the damage within the incubation period and mass loss rate. Like in the case of a single hydrofoil we also observed dependency of the cavitation erosive aggressiveness on the size and dynamics of cavitation structures. Results presented in these studies will serve as a basis for achieving the final goal of the ongoing work—to develop a method that will enable accurate prediction of cavitation erosion with minimal experimental effort or even solely by using computational fluid dynamics.