Hydraulic characteristics of the combined step dissipator with trapezoidal energy dissipation pier

Step spillways have been used in the construction of small and medium-sized reservoirs, particularly with the concrete dam construction. The steps have been widely applied on the smooth spillway to increase the gas doping for energy dissipation through the violent turbulence of the water body. In this study, a combination of energy dissipating piers and steps was proposed to further improve the energy dissipation of the spillway, and then reduce the negative pressure on the step surface. The trapezoidal energy-dissipating piers were arranged at the convex corners of the steps. The model test and numerical simulation were used to investigate the flow pattern, flow velocity, pressure, and energy dissipation rate of the combined step energy dissipator under single-row and single-row staggered arrangement. The hydraulic characteristics were compared with the traditional step energy dissipator. The results show that the flow pattern of the combined step dissipator with the trapezoidal energy dissipation pier was basically the same as the traditional at the different relative critical water depths. The energy dissipation pier was arranged at the convex corner of the step, compared with the traditional one. The energy dissipation pier shared a provocative effect on the water flow in the transitional flow state, in order to enhance the energy dissipation. The pattern of the small bottom and large surface layer was found in the distribution of water flow velocity in the step cross-section of the trapezoidal energy dissipation pier combination. The range of flow velocity was expanded by about 2.4-3.1 times, compared with the traditional. In the position close to the step water surface, the water flow velocity of body type Ⅰ, and Ⅱ step energy dissipation were reduced by about 3.6% and 5.2%, respectively, compared with the traditional. The water flow was reduced on the step energy dissipation worker of the damage of the scouring. The negative pressure range of trapezoidal energy dissipation pier combination of step energy dissipation worker was reduced by 60% to 70%, of which the body type Ⅱ step energy dissipation worker produced the smallest value of the negative pressure, compared with the traditional. The negative pressure value of the body type Ⅱ step energy dissipator was the smallest, which was 42% less than that of the traditional. The cavitation damage was effectively reduced on the vertical surface of the step. The energy dissipation rate of the combined step energy dissipator decreased less than before with the relative critical water depth increasing from 0.714 to 1.486. The energy dissipation rate was still 70% or more under the condition of larger relative water depth. A better characteristic was achieved in the energy dissipation. The findings can also provide some references for practical engineering.