Experimental Study of Mechanism of Silt Abrasion Influenced by Cavitation in Hydraulic Machinery

Experiments of cavitation erosion, silt abrasion and their synergetic erosion on Al hydrofoils were made in a testing-section. The erosion depth on hydrofoils was measured, and results showed that the depth value increased gradually with the condition changed from silt abrasion to synergetic erosion (lie due to contemporary action of silt abrasion and cavitation bubble collapse) and meanwhile with the position changed form the front part to the trailing edge of hydrofoil. The microtopography on hydrofoils was observed under the three experimental conditions. The cavitation erosion results appeared as regular-shape pits which differed only in the number per unit area at different position. The silt abrasion patterns was uniform in characteristics around one fixed point on hydrofoil. From the front part to the trailing edge of hydrofoil, the main abrasive wear patterns changed from ploughing type to wedge type. Small scale ploughing or cutting type and large scale wedge type were the main erosion patterns of the synergetic erosion directly caused by solid particles. From the front part to the trailing edge of hydrofoil, the size of small and large scale abrasive wear patterns increased gradually. Combining the analysis and processing of cavitation structure with the silt abrasion and synergetic erosion patterns, a viewpoint about silt abrasion influenced by cavitation was put forward. During the stage of growth of attached cavity, the hydrofoil was eroded by solid particles at small angle as a result of solid particles subjected to cavitation nucleation being accelerated along the surface of hydrofoil, and the erosion patterns were dominated by ploughing or cutting type. During the stage of cavitation cloud collapse in main flow, the hydrofoil was eroded by impact abrasion of solid particles at large angle resulted from solid particles being accelerated to high velocity by micro-jet or pressure wave, and the dominating erosion pattern was wedge type.