Retrofitting of Pressurized Sand Traps in Hydropower Plants

Unlined pressure tunnels in sound rock, combined with pressurized sand traps at the down-stream end, allow for low-cost construction of hydropower tunnel systems. This design concept is utilized in hydropower plants across the world. Currently, many such power plants are being upgraded with higher installed capacity, which may result in challenges with the sand trap effi-ciency. A physical scale model test, accompanied by 3D CFD simulations of a case study pres-surized sand trap, has been studied for economic retrofitting. The geometric model scale is 1:36.67 while the velocity scale and sediment scale are 1:1 (same average flow velocity and sed-iment size in model and prototype). This is currently an uncommon scaling approach but with several advantages, as presented in this paper. Various options for retrofitting were investigat-ed. A combined structure of ramp and ribs was found to significantly improve the sediment trap efficiency. The main novelties from this work are the proposed design of the combined ramp and rib structure. Secondary results include an efficient setup for physical scale models of pres-surized sand traps and a methodology that combines the benefits of 3D CFD simulations with physical scale models testing for sand trap engineering and design.