Study On Configuration Of Ogee Surface In Reconstruction Project Of Water-supply Tunnel In Huangyanghe Reservoir

Ogee surface is widly used in release structure of water conservancy and hydropower project. For example,it is used in open flow section of conduit behind outlet with pressure, open flow spillway, weep-hole in dam and so on. It links two different sections and causes water flow through it naturally. Because of undering centrifugal force, water flow will jump up and water pressure in floor will decrease even result in cavitation damage if improper Ogee curve is used. So it is very important to study on the hydraulic characteristic of Ogee section and the method to design Ogee curve.According to the basal data of current Huangyanghe reservoir conduit and the primary reconstruction plan obtained from design institute, hydraulics model is built in laboratory. Through model tests, the flow state in chute of current project is observed and some hydraulic parameters are measured. Bad flow state that has been observed in prototype project is demonstrated commendably. The primary reconstruction plan is tested. This chute can only fit the need of safety operation under normal water level when the service gate is full opened. The fatted Ogee surface is brought out and tested. It can fit the need of safety operation under all water level when the service gate is full opened. But the velocity is higher when the gate is partly opened than that of full opened. The amount of construction is too large if Ogee surface is calculated with velocity behind partly opened gate.After the principle of Ogee curves for flow with horizontal muzzle velocity has been analysed, the coefficient C of all tested Ogee curves are calculated. It is made clear that the coefficient C needs to be at the range of 1.3 to 1.5 when the service gate is full opened. Trajectories of different velocities at beginning section on the fatted Ogee surface is calculated. Rationality of using the maximal velocities at beginning section to design Ogee curve is demonstrated. Formula to calculate coefficient C is deduced.When Ogee curve of flow with horizontal muzzle velocity can not solve the problem, this paper analyses Ogee curves of flow with oblique muzzle velocity and find this kind of curve can lower the floor of chute greatly. A series of curves of different initial angle are compared with the current chute. The curves with jet angle 10°~20°are more closer to the current chute. It is feasible to use this kind of curve to solve the problem.In order to use that kind of curve connecting different slopes on canal, water flow is changed downward at the section upstream outlet. This kind of chute is proved can do well at all characteristic operating conditions When the curve with jet angle 11°and the curve with jet angle 20°are tested. The applied Ogee surface is provided according to actual situation of the reconstruction project. Pertinent hydraulic parameters under all characteristic operating conditions for the applied water-supply tunnel are observed and measured. These parameters are flow pattern, water surface line, water pressure and flow velocity. Aeration depth in chute and cavitation number of the chute's floor is calculated. This test proved that the applied tunnel can fit the need of safety operation under all characteristic operating conditions.