Design Optimization of Spillways at Baihetan Hydroelectric Dam

Sammanfattning: China’s economic prosperity has led to a massive development in the hydropower sector. The Baihetan hydropower project is an ongoing construction and will become the third largest hydroelectric power plant in the world in regards to generating capacity and is projected to be finished in the year 2020.For every fault that an investment this massive has, it will lead to enormous cost and safety risks. Therefore the standards for every detail are especially high to ensure the success of its future operation. One of the risks is from the water jet impact on the downstream stilling basin that can cause erosion on the riverbed. The evaluation of this risk has previously been carried out by an experimental scaled model at the Department of Hydraulic Engineering at Tsinghua University in Beijing, China. This thesis will however evaluate the potential of exposing these risks and analyzing methods to minimize them through Computational Fluid Dynamics analysis.A Computational Fluid Dynamics model of a surface hole spillway was created in order to be compared and validated against the experimental results. The results in longitudinal direction are in good agreement with the experimental results, with an accuracy of the numerical model being 91% for the longitudinal distance and 98% for the longitudinal spread. The spread in the transverse direction was however inaccurate with a 40% accuracy in comparison to the experimental results. With a satisfying accuracy in longitudinal direction and a known error in the transverse direction, the numerical model can be used as an initial study for optimization by the implementation of a chute block.After the numerical model was validated against the experimental results, the spillway was redesigned with a chute block to compare performance compared to the original setup. With the chute block spillway, the trajectory of the water jet was angled away from the stilling basin’s center, and the longitudinal spread of the water jet at the impact with the stilling basin increased by 3 m, an increase of 34%. An average maximum dynamic pressure of 1,9 MPa was located in the center of the bulk flow. With the chute block, the pressure impact was located 2 m further away from the dam toe.The results from this thesis shows potential in usage of CFD models in order to evaluate water discharge performance and that the integration of a chute block shows promise in improving the efficiency of the spillway. However, the inaccuracies of the numerical model only make it viable to use as an initial study of design optimization and cannot replace physical scaled models. In order to make final conclusions the model must be improved further, and with tools of high capacity computational power, the model could be improved and simulate results closer to reality.