Effects of jet impact angle on cavitation erosion intensity and cavitation cloud dynamics

Cavitation water jet technology has been widely used in industrial production, but the effects of cavitation cloud evolution and erosion patterns at different impact angles remain to be determined. To study the erosive effects of cavitation jets at different impact angles, this study conducted erosion experiments with different impact angles. The flow conditions are varied at 45 degrees, 60 degrees, 75 degrees, and 90 degrees, four different jet impact angles on the target surface at the optimal standoff distance. The influence of impact angle on the erosion effect was explored by erosion morphology and erosion quality. Larger mass loss occur under erosion conditions at larger impact angles (75 degrees and 90 degrees), while relatively less mass loss occurs at smaller impact angles (45 degrees and 60 degrees). Furthermore, the evolution of cavitation clouds at different impact angles is illustrated through high-speed visualization experiments. The changing of cavitation jet structures is investigated by Proper Order Decomposition(POD) analysis. The smaller the impact angle, the closer the position of the re-entrant jet is to the nozzle, which leads to an increase in the frequency of cavitation cloud shedding. Meanwhile, cavitation bubbles don't have enough time to develop, resulting in reduced erosion capacity. The behaviour of the cavitation jet impinging on the target at different impact angles is simulated by the Large Eddy Simulation (LES) turbulence model. As the angle decreases, the pressure fluctuation caused by the cavitation cloud on the target surface decreases, and the duration also decreases accordingly. The results of this study provide technical support for the application of cavitation jets under different impact angle conditions and also help to understand the cavitation erosion mechanism under different impact angles.