Author(s): Hongwei Zhang; Zhigang Wang; Dong Zhang
Keywords: Baffle drop structure; Hydraulic characteristics; Model test; Numerical simulation; Deep tunnel
Abstract: Vertical shafts, a drop structure which direct flow from shallow surface sewers to deeper tunnel by gravity, combine the collection system and deep tunnel to make a complex hydraulic system. Recently, Baffle-drop structure has been widely used for its advantages such as proper energy dissipation, hydraulic stabilities and better ventilation performance and etc. In this study, numerical simulation and physical model tests were carried out to study the hydraulic characteristics of the baffle shaft. The physical model was setup according Froude scaling 1:15 with 31m3/s design discharge in prototype. 3D numerical simulation was performed by using the commercial Computational Fluid Dynamics (CFD) code FLUENT with usingκ-εturbulence model and VOF interface-processing technology. The results showed that baffle shaft has ideal flow patterns in a wide flow range. Instead of a single plunge pool or impact cup at the bottom of the shaft, baffle shaft can form a water cushion on each layers to dissipate the falling water energy effectively. Furthermore, it was found that the negative pressure occur usually on the lower surface of the baffle edge and at the top of the deep tunnel entrance, and existence of the port is helpful to reduce the negative pressure value in the wet side and enhance the hydraulic stability. The study also demonstrated that improper design can cause great mount of air entrainment into deep tunnel, and a suggestion was put forward for construct arrangement to minimize the air entrainment.