Investigating the Effect of Different Arrangements of Obstacle on the Stepped Spillway on Flow Characteristics and Energy Dissipation

This study has investigated the effect of roughness such as screen and 3D-porous obstacle with different arrangements on steps, 3D-porous obstacle, and continuous obstacle at the edge of steps in two slopes of 1:2 and 1:3 for all three regimes in the stepped spillways. The image processing results showed that the roughness of the spillways makes the recirculation zone under the pseudo-bottom smaller and a transparent region is formed in the inner corner of the spillway where there is no air bubble. Moreover, adding roughness on bottom and placing the 3D-porous obstacle and continuous obstacle on the edge of step in the step spillway cause the inception point of free aeration move down to the downstream compared with flat steps on both slopes. The placement of the 3D-porous obstacle and screen in all arrangements, as well as the continuous obstacle and 3D-porous obstacle on the edge of the spillway at 1:2 slope do not have a positive effect on the energy dissipation on transition and skimming flow regimes; however, by placing the obstacle at the edge of the spillway with a 1:3 slope, the dissipation performance of the spillway increased for all three regimes with an average of +5%.