Numerical study on the evolution of cavitating flow and collapse-induced erosion characteristics in high-speed hydraulic tunnel

While hydrodynamic cavitation and the associated erosion during cavity collapse have received significant attention, existing research has predominantly focused on small-scale geometries like Venturi tubes. In this study,afirst high-resolution numerical simulation is conducted to investigate cavitation and erosion phenomena within a large-scale, high-speed hydraulic tunnel.We employthe large eddy simulation approachto investigatethe characteristics of cavitation structures under varying cavitation numbers.The study elucidatesthe pressure loss process induced by cavitation blockage flow, anddiscussesthe vortex-induced cavitation mechanism along with the feedback effect of cavity collapse on vortical structures. Ata representative cavitation number of 0.89, the cavitation dynamics are dominated by a spatially partitioned coexistence mechanism of condensation shock and re-entrant jet-induced shedding. This partitioning phenomenon is primarily attributed to the tunnel's asymmetric geometry and the significant gravitational effects inherent to large-scale hydraulic tunnels. Novel methods based on physical theory are proposed for identifying cavity collapse regions within the flow field and predicting wall erosion risk regions;these methods have beenexperimentally validated. The wall erosion risk under the condensation shock shedding cycle is found to be significantly higher than that under the re-entrant jetcycle. Furthermore, wall erosion in hydraulic tunnels is more likely to occur near the boundaries, with high-risk areas concentrated primarilyin the downstream regions. Conversely, cavitation occurs withintheextensive middle regions of each wall. This disparity arises because cavitation initiates more readily on smooth surfaces, whereas collapse-induced erosion is favored in pressure recovery zones.