明渠无压隧洞进口过渡段水力特性研究OA

In open-channel water conveyance projects,the unpressurized tunnel inlet is often connected to tunnel body through a contraction transition section,and their geometric configuration significantly impacts the local hydraulic characteristics of the inlet section and the overall conveyance capacity.Regarding the significant water level fluctuations observed at the tunnel inlet of a large-scale water conveyance project under the design discharge,this study employs three-dimensional CFD numerical simulations to replicate the unfavorable flow patterns in the inlet section.The investigation reveals the underlying mechanisms,systematically analyzes the influence of the geometry parameters of the transitional contraction section on the hydraulic characteristics,and subsequently proposes corresponding optimized design recommendations.The research results indicate that the original 25° contraction angle design of the tunnel inlet transition section induces significant flow contraction waves,leading to periodic water surface fluctuations and insufficient freeboard in certain tunnel sections.Based on the comprehensive optimization of both the contraction angle and the connecting geometry,it is found that head loss can be significantly reduced and water level fluctuations effectively eliminated.Among these factors,the connecting geometry plays a particularly prominent role in mitigating both water level fluctuations and head loss.For existing projects,simply incorporating an arc-shaped connection at the end of the transition section can reduce the fluctuation amplitude by 62.5%and lower the local head loss coefficient to 0.1.This demonstrates that significant hydraulic improvement can be achieved with relatively minor modifications.