Observations on jet flipping below a sluice gate

It is a necessary to investigate effects of scour downstream of many hydraulic structures, especially in an erodible sediment bed below that structures. This explains the reason why we need to get deeper understanding about the intense local bed degradation by observing the scour characteristics in this project. Experiments were carried out on scour downstream of a sluice gate with varying apron length. The runs were recorded and the scour characteristics as well as a jet flipping phenomenon were studied via the recorded videos. Most of the runs have an appearance of jet flipping except the runs where the apron lengths are extremely short or extremely long. The flow pattern depends on the apron length and it is showed that there is a critical range of apron lengths along which jet flipping would occur and beyond this range we cannot observe any jet flipping phenomenon. The interchange between water jet direction, from bed to water surface and vice versa, makes the jet flipping phenomenon happen. The scour hole is formed before the jet flipping is observed and the shape of scour hole is continuously changed during scouring process with different apron length per each cycle. Each cycle consists of a digging phase and a filling phase. The digging phase creates a scour hole while the filling phase fills the hole until the next jet flipping cycle with the dig-fill processes being repeated. In this study, the starting time and ending time of digging phase and filling phase of every cycle were taken down. The scour hole shapes in the end of each phase were captured and its volume were calculated. And there are discussions about the collective effects of parameters such as tail water depth, water jet velocity and apron length in the occurrence and frequency of jet flipping. There are also numerous diagrams, which were created from extracted data using WinDIG, and are useful to describe the flow directions, velocity distribution and centreline scour profiles during the digging phase and the filling phase. These diagrams provide clearer visualisation of the flow fields, therefore, the jet-flipping phenomenon could be understood better.Bachelor of Engineering (Environmental Engineering