Designing real-scale spillways to avoid supercritical flow
Overview: Labyrinth spillways are very efficient in channeling water flood flows to protect urban areas. Form the design viewpoint, the discharge efficiency of the spillways depends significantly on their configuration. Advanced CFD modeling is now acknowledged as an affordable and accurate way to optimize spillways characteristics since it allows investigating the impact of different flow conditions and various configurations at low cost and in short delays, compared to lab-scale measurements.
The challenge: The engineering challenge here is to accurately predict the flow discharge and hydrostatic pressure distribution downstream of the weir. The height and mass flow rate of the water stream upstream the weir is important as well and dictates the discharge efficiency of the spillway. These are translated into a quantity referred to as Upstream head (vertical distance from weir top surface up to the unaffected upstream water flow surface) vs. Discharge (volume flow rate of water). The engineers need also to know about the exact flow conditions (for the specific spillway configuration) that may lead to supercritical flow conditions (i.e. causing floods downstream).
TransAT Solution: The simulation is based on solving the multiphase flow equations for free-surfaces in 3D, with water and air flows being both resolved. In this case the phase-average homogeneous model is employed, which is cheaper in terms of computer resources than interface tracking. The turbulent flow is modeled with the V-LES approach. The simulation of a 1:15 Froude-scale sectional model was advanced in time for 10s. The simulation results were validated against experiments and showed very good agreement, in particular as to the Upstream head: TransAT 9.15 ft; Exp. 8.7 ft.
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Dr Karol Swiderski
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