Test Study On Morphology Of Downstream Scour Hole Of Dangka Hydropower Station

Hydropower is a kind of clean energy that occupies important position in Chineseenergy structure. In recent years, with rapid development of economy, people’s demands forwater and electricity keep increasing, and in order to adapt to these needs of society, low-headhydropower stations get developed rapidly and have increasingly become a particularlyimportant direction of hydropower development. The low-head hydropower station projectwith some characteristics, such as low head, large flow, low Freund’s number, deep tail waterand low energy dissipation and etc., In the low-head hydropower dam station, the water flowstill possesses relatively large residual energy even after passing through energy dissipationfacilities. As a result, large amounts of sediment on the river bed will be scour away andfurthermore to form various-shaped scour holes on downstream, which caused the part or ofthe project seriously damaged. Therefore, it is important to understand the equilibrium shapeof scour pits correctly for ensuring security and stability of hydro-junctions.Based on the model of Dangka hydropower station, some groups of experiment atdifferent discharges and bed material gradations were conducted. The local scour pit shapesdownstream of flood sluice were studied and the formation mechanism of local scour on thedownstream was analyzed. The major findings of this thesis can be reflected as follows:(1) After collecting experimental data, the relationship between scour pit shape and itsaffecting factors like discharged flow, river bed material gradation, flow patterns at the end ofstilling basin, the stilling basin base plate height and gate opening were analyzed. WhenFroude numbers of apron ends are very similar, the slopes of scour hole relatively consistent.(2) The sediment angle of repose is measured by using plate pulling method, and theequations of sediment repose angle with sediment both in water and air are obtained. Basedon dimensional analysis and multiple regression analysis, the relationship between dynamicwater Angle of repose in the scour pit and water flow velocity v, water depth h, sedimentdiameter d50are acquired, and it has a high precision to forecast the downstream slope of thepit verified by experimental data.(3) Based on the theory of mechanics, the equations to calculate incipient velocity ofsediment on the dorsal surface of scour holes including sliding start mode and rolling start mode are deduced. Compared equations of two different modes found out the structure of twoequations are basically same. Verified the two equations with experimental data and provedboth of them are feasible.