Experimental Investigation On Energy Dissipation By Flaring Gate Piers On Spillways And Slit-Type Bucket On Bottom Level Outlets In High Arch Dams

The characteristics of high arch dams project in China are high water head, large discharge, narrow valley, so energy dissipation of them is notable and one of key factors of project disposal. In order to alleviate the value of the plunging pressure caused by plunging jet from dams effectively, plunging jet should be dispersed in the receiving pool. But it is very difficult to make the plunging jet from high arch dams diffuse laterally in canyon area. This paper brings forward energy dissipation by flaring gate piers on spillways and slit-type buckets on deep level outlets, and three types of and flaring gate piers and three types of slit-type buckets are designed for experiment. The results of energy dissipation are compared with the results of energy dissipation by top apertures differential bucket and collision of plunging jets of spillways and bottom outlets. Several conclusions are as following:1. The energy dissipation by flaring gate piers on spillways and slit-type bucket on bottom level outlets is presented. Because of the separation of nappes in the direction of longitude, the effect of energy dissipation is improved remarkably, and the values of the plunging pressure in the receiving pool are alleviated effectively. In addition, because of the interleaving of top and bottom nappes, there is no bump in the air, the finite width of spillways can be fully utilized, and flood discharging atomization caused by bump of nappes can be weakened.2. The flow pattern will present different form because of the flaring gate piers on spillways. When the water level of reservoir is low, there is no effect on discharge capacity when use the flaring gate piers, while when the water level is high, flow pattern is subcritical flow for backwater, and discharge capacity is influenced, therefore the spillway drainage coefficient increases and then reduces when the water level increases continually.3. On condition that the use of flaring gate piers dose not influence discharge capacity of spillway , and the shrinkage ratio is less than 0.5, the values of the plunging pressure in the receiving pools are all reduced basically.4. The critical hydraulic head of slit-type bucket on bottom level outlets that just can cause deflecting is mostly influenced by shrinkage ratio and deflecting angle. The critical hydraulic head heightens with the increasing of deflecting angle or decreasing of shrinkage ratio. When the hydraulic head above slit-type bucket bottom plate is lower than critical hydraulic head, hydraulic jump appears at outlet reach of free flow.5. Because the operation hydraulic head of slit-type bucket on bottom level outlets is high, the flow pattern of jet flow easily forms. Just because of this, the values of the plunging pressure in the receiving pool have not outstanding differences under three kinds of slit-type bucket conditions. Comparatively, with the reducing of shrinkage ratio of slit, the shock loads of receiving pool reduce, but the critical hydraulic head that just can cause deflecting heightens simultaneously.6. The deflecting angle of slit-type bucket on bottom level outlets should not be too big, otherwise the separation effect of nappes in the direction of longitude is influenced, and consequently the values of the plunging pressure in the receiving pool increase relatively.