Seite - 1080 - in Book of Full Papers - Symposium Hydro Engineering

BELL-MOUTH SPILLWAY The overflow piers of the Jirkov Dam bell-mouth spillway were constructed rather small in size compared with similar structures at other dams. The piers also force water to rotate in the opposite direction. The water falls to the vertical shaft and then flows to the outlet tunnel via the sharp perpendicular bend that was suspected to limit the capacity of the whole object. 3. RESEARCH ASSIGNMENT The unusual spillway intake setup led to the research that was carried out by the Civil Engineering Faculty of the Czech Technical University in 2015 and 2016 [1]. The research was ordered by the dam operator Povodí Ohře, state enterprise. The aim of the research was to assess the existing layout and propose optimized design. The research was carried out using the physical model of the bell-mouth spillway that extended from the top of the structure to the end of the spillway tunnel at the downstream toe of the dam. The physical model was used to derive the rating curve of the spillway and particularly to find the level flow at which the undesirable hydraulic effects occur. It was also used to design and verify suitable modifications to the intake of the bell-mouth spillway, to the bottom end of the vertical shaft and to join of the bottom outlets to the spillway tunnel. The physical model was built using the Froude similarity, it was considered that gravity and inertial forces are dominant and effect of remaining forces such as kinematic viscosity are small. The model was built in laboratories of the Czech Technical University in Prague, Faculty of Civil Engineering at a 1:20 scale. Setup allowed to measure not only flows, but also vibrations and pulsations. Pressure sensors were used to measure all hydraulic phenomena, which occurred on the model and particularly the dynamic effects of water flow on the structure. Firstly, the measurements were carried out on the model of the original design and then modifications reflecting the knowledge gained on the modelling of similar bell-mouth spillways were proposed and tested. In particular, the attention focused on the optimization of the shape of overflow piers and the rounded bottom end of the vertical shaft. 1080