Experimental Investigation On Joint Application Of Stepped Energy Dissipater With Auxiliary Dissipater

Affected by terrain and work amount, some projects choose stepped spillway as the main energy dissipation part, which are the optimal choice. Though the energy dissipation rate of the stepped spillway is 40 to 80% higher than that of the smooth spillway, it accompanies with a prodigious amount of energy when the water falls down due to a relative high height of water, which may lead to a serious scour in the underwater bed. To maintain the effect of the energy dissipation and avoid building a deep and lengthy stilling basin to save project investment as well, this paper proposes a scheme which unites the stepped spillway energy dissipater and the auxiliary energy dissipater together combining with two Sinkiang Water Control Projects. The paper integrates a theory analysis and hydraulic model test together to research systematically on hydraulic features under the coalition of the stepped spillway energy dissipater and the auxiliary energy dissipater. The achievements of the paper include several sides:(1) Summarize the significance and progress in recent decades of the outlet structure energy dissipater, the characteristic and prerequisite of the spillway ski-jump, underflow and stepped energy dissipation. Propose the coalition of the stepped energy dissipater and the auxiliary energy dissipater by taking examples from the coalition of various energy dissipaters and combining with the superiority of the auxiliary energy dissipater.(2) Summarize the discriminant of the stepped spillway's flow regime, and the calculated mode of aeration primary point, aeration rate and energy dissipation which are proposed by domestic and overseas scholars, to provide reference for the related project.(3)The measurements of the pressure on the stepped spillway demonstrate that the valve and the distribution of the pressure are closely related to the pattern and the depth of the rotating flow on the steps. And the reasons for the negative pressure are analyzed in this paper.(4) Factors that affecting the distribution of velocity and water surface are weir surface curve, the cohesive devices of weir and stepped spillway, aeration characteristics and gradual dissipation, it's based on the model experiment measurement results. It also gives a concise summarization of the water depth and velocity variation law along the spillway.(5) For a relatively low unit discharge which can also cause serious scouring damage because of downstream low water level, a proposal combining stepped energy dissipater with baffle block is recommended. For an overflow dam with the characteristics of high water head, large discharge and large power, the problems of energy dissipation and scour prevention are serious. Therefore, in this paper, a proposal combining stepped energy dissipater with baffle still and baffle block is recommended. The model experiment results demonstrate that the baffle block can effectively break the main flow into small pieces, through the friction and collision between the water and the baffle blocks, the depth and velocity are greatly uniformized. While the baffle still appropriately installed on the downstream apron can increase the water depth, improve the flow regime, eliminate complementary energy and water fluctuation and make the smoothly cohesion to the downstream possible. The experiment results indicate that the energy dissipation ratio of the joint application of stepped energy dissipater with auxiliary dissipater is satisfactory. On one hand, it decreases the scouring of the downstream channels and ensures the safety of the entire building; on the other hand, it remarkably decreases the size of the stilling basin, which in turn decreases the investment considerably, a new solution for the flood discharge and energy dissipation in practical projects can be provided based on this paper.