Start Date

2018 8:40 AM

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

The Hong Kong West Drainage Tunnel (HKWDT) system consists of 34 storm water intake structures designed to intercept storm water runoffs in upland catchments. During storm water events, each of these intake structures intercepts and diverts the upstream supercritical flow into a bottom rack chamber connected to a supercritical vortex drop. To satisfy the minimum environmental flow requirement in dry weather, small surface runoffs are intercepted by an inclined barrier across the main channel, and conveyed to the downstream drainage system through a 300mm wide low flow channel along one side of the intake. When the intakes are in operation during rainstorms, observations suggest that the storm water runoffs being conveyed via the low flow channel might be more than originally designed. The objective of the present study is to assess the hydraulic performance of a typical intake structure in HKWDT via three-dimensional computational fluid dynamic (CFD) modelling. Numerical simulations are carried out using the volume-of-fluid (VOF) method in FLUENT software for a range of storm inflow condition. The un-intercepted flow rate are determined from CFD results and compared with experimental results of a 1:12 undistorted model in laboratory. The predicted water level and un-intercepted flow agree well with measurement. It is found that the ratio of un-intercepted flow to the total flow decreases with increasing inflow. The model results show that in typical rainstorm event the supercritical inflow impinges on the barrier and is deflected upwards. Part of the flow spills to low flow channel, resulted in undesirable higher flow to the downstream. In large flow rate scenarios, the effect of the barrier is less significant due to the increase in flow depth.

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May 17th, 8:40 AM

3D Numerical Modeling of a Supercritical Intake With a Flow Diversion Barrier

The Hong Kong West Drainage Tunnel (HKWDT) system consists of 34 storm water intake structures designed to intercept storm water runoffs in upland catchments. During storm water events, each of these intake structures intercepts and diverts the upstream supercritical flow into a bottom rack chamber connected to a supercritical vortex drop. To satisfy the minimum environmental flow requirement in dry weather, small surface runoffs are intercepted by an inclined barrier across the main channel, and conveyed to the downstream drainage system through a 300mm wide low flow channel along one side of the intake. When the intakes are in operation during rainstorms, observations suggest that the storm water runoffs being conveyed via the low flow channel might be more than originally designed. The objective of the present study is to assess the hydraulic performance of a typical intake structure in HKWDT via three-dimensional computational fluid dynamic (CFD) modelling. Numerical simulations are carried out using the volume-of-fluid (VOF) method in FLUENT software for a range of storm inflow condition. The un-intercepted flow rate are determined from CFD results and compared with experimental results of a 1:12 undistorted model in laboratory. The predicted water level and un-intercepted flow agree well with measurement. It is found that the ratio of un-intercepted flow to the total flow decreases with increasing inflow. The model results show that in typical rainstorm event the supercritical inflow impinges on the barrier and is deflected upwards. Part of the flow spills to low flow channel, resulted in undesirable higher flow to the downstream. In large flow rate scenarios, the effect of the barrier is less significant due to the increase in flow depth.