Experimental Study on the Geometric Effects of the Baffle Blocks in Stilling Basin on the Hydraulic Jump Characteristics Downstream of Smooth and Stepped Chutes

Hydraulic jump phenomenon is a rapid variation in flow conditions that occurs for dissipation of the kinetic energy of the flow in downstream of the hydraulic structures in stilling basins. The aim of this study is to investigate flow characteristics of stepped and smooth chute and the effects of block geometry on the hydraulic jump characteristics in the stilling basin USBR III. Experiments were conducted on the stepped chute and they were compared with smooth chute as well as stilling basin and baffle blocks and end sill in different geometry shapes to test the hydraulic behavior of different hydraulic conditions. The results were compared with stilling basin without block. The results of comparing the two types of chutes showed that in stepped chute, the air entrainment inception locations a positioning further upstream than the smooth chute due to the turbulence of the flow on the steps. The energy dissipation and Darcy roughness coefficient in stepped chute increases by 10% and 15.6% on average compared to smooth chute, respectively, which indicates the appropriate hydraulic performance of stepped chute compared to smooth type. Results showed that increasing the Froude number and height of the baffle blocks caused decreasing sequent depths ratio and the jump length by 22.12 and 36 percent, respectively, compared to classical jump. It is believed that the main reason was raising the rate of secondary flows and flow resistance due to the baffle blocks in stilling basin. The energy dissipation increased by 24 percent, compared to the classical jump and further increase in high Froude number.