Effect of deflector and crest geometry on submerged flow in a shaft spillway

Abstract

In this study, the impacts of a deflector located in the throat and inlet geometry of the crest on improving the hydraulic performance of a shaft spillway were investigated, and the hazards induced by the lack of timely drainage of floods in dam reservoirs were decreased to some extent. To investigate the deflection effect, three constriction specimens in the shaft throat with constriction area-to-shaft area ratios (A_d/A_i) of 0.75, 0.5 and 0.25 were considered as scenarios. In each scenario, the flow conditions through 12 different spillway specimens with crown wheel inlets were tested, and the results were compared with the flow conditions in crown wheel spillways without a deflector (reference model). The results showed that the use of a deflector has an important role in reducing vortex flows, stabilizing changes in the water level of the reservoir and increasing the discharge coefficient of the flow. Studies on reference models have also shown that crown wheel inlets (C.W.) improve shaft spillway performance, with C.W. spillways having an average discharge coefficient 32% greater than that of shaft spillways. Finally, considering the optimal deflector factors and C.W. geometry, an optimal model was proposed for flood reservoir conditions.