Flow Characteristics of Submerged Orifice for On-site Detention Facility with Drowned Outlet (In Drainage System)

Tang, Evon Ee Wen (2017) Flow Characteristics of Submerged Orifice for On-site Detention Facility with Drowned Outlet (In Drainage System). Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

This study focuses on the application ofsubmerged orifice to improve retarded runoff from drowned outlets. A drowned outlet is common in riverine area. The drainage discharge outlets are often submerged by river water as the river water level fluctuates during high tides or monsoon seasons. Due to the difficulty of the runoff being discharged towards the river, it then fills up the drainage system in a faster way. This results in runoff spiUing out of the drains and hence causing flash floods. Towards this end, an on-site detention with submerged orifice has been tested to improve the retarded runoff from drowned outlets. The workability of the submerged orifice is investigated with experimental set ups and visualization with Computational Fluid Dynamics (CFD) simulations. The application is then demonstrated through a real-life case study at Kuching Waterfront and Main Bazaar. The prototype with submerged orifice is tested under different velocities of perpendicular tailwater flows, which represent high and low streamflows. The flow characteristics of submerged orifice are also observed and compared with CFD simulations. The experimental works show that with differences in headwater and tailwater levels, the pressure exerted on the levels has caused an energy build-up; as such, water from a region of higher pressure flows towards a region of lower pressure. Hence, it ensures continuous full flow of water out of the on-site detention storage. Even more so, it shows that the submerged orifice discharge rate increases as perpendicular tail water flow increases. But the increment is very small, which can be said that the perpendicular tailwater only influences the orifice flow patterns but not a hindrance to orifice discharge. Furthermore, CFD simulations show the flow patterns in full scaled prototype is a repetitive trend oflaboratory outcomes. Therefore, submerged orifice can possibly be used to improve retarded runoff from drowned outlets. III Sustainable development along the Kuching Waterfront and Main Bazaar could be achieved by an ideal design ofsuch on-site detention with submerged orifice.

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