Author(s): C. K. C. Wong; D. Y. Yu; J. H. W. Lee
Linked Author(s): Joseph Hun-Wei Lee
Keywords: No Keywords
Abstract: In densely populated cities, urban flood control often requires the use of compact drainage structures. A compact bottom rack chamber and vortex drop intake structure is newly developed for diverting fast moving turbulent flow on steep catchment into a drainage tunnel for discharge into the sea. The flow in the bottom rack structure is three-dimensional, turbulent and highly aerated; the hydraulics of such a structure has hitherto not been studied. The complex flow is investigated by comprehensive experiments and three-dimensional computational fluid dynamics (CFD) modeling using the FLOW3D software. The air-water flow is simulated using the Volume of Fluid (VOF) method; turbulence closure is made via a two-equation k–ε model. It is found that the numerical model is able to simulate the observed major flow features in the bottom rack chamber-the supercritical inflow into the chamber gives rise to a spiral circulation that is re-directed to impinge on the inflow jet, leading to significant turbulent mixing and air entrainment. The supercritical outflow into the link channel is highly non-uniform. The air concentration in the bottom rack chamber is found to decrease with discharge flow. Numerical predictions of the average air concentration are in good agreement with experimental data.