Research On Composite Energy Dissipation System Of Multi-plunge With Bottom-flow In Bended Spillway

Spillway, the most widely used discharge structure in hydro project, is generally designed bilaterally symmetrical with a linear axis. However, under some circumstance, due to the topography and geology condition, layout, discharge condition or cost and so on, spillway with bends becomes the best option. The flow in bend with very complex hydraulic characteristics moves in three-dimensional spiral turbulence, which is a big challenge for the energy dissipation of the spillway.This thesis summarizes the study status related to the hydraulic characteristics of flow in bends. Moreover, the calculation formula and variation pattern of the longitudinal gradient, transverse slope, transverse circulation and supercritical shock wave are briefly introduced. Based on the theory research, methods used to eliminate or inhibit the shock wave in practical projects are introduced.According to the different layout of the original and reconstruction scheme for the curved spillway of one reservoir in Liaoning province, comparison has been made based on the combination of model experiment results and theoretical analysis. The factors that matter are fluctuating pressure, flow regime, distribution of water depth and velocity and rate of energy dissipation.l.To eliminate the transverse ultra-height and ameliorate the flow regime about the original scheme of bending spillway in one reservoir, the optimization scheme, which is the combination of various dissipaters including stilling ridge, plunge pool, T-shaped pier and diversion pier, has been determined based on the comparison of six optimizing schemes. The results of the model test show that the flow regime is good and the rate of energy dissipation is satisfying. However, the arrangement is too complex which increase the difficulties of construction and the engineering costs. Therefore, reconstruction becomes the alternative option.2. In view of the natural ridges that lie in the terrain, the spillway is redesigned in a body type of five-stage drops to implode the elevation difference. This kind of design makes the full use of the terrain and reduces the engineering quantity. Under the joint action of gravity and centrifugal force in bending section, the depth of water besides the right wall is much deeper than the left wall. Due to the deflection of the right wall, the water in the downstream of the curves section is concentrated on the left bank, the mainstream moves in an "S" shape routine, first right, then left.3. Referring to relevant engineering experience, the composite dissipation system of two-stage stilling basins is recommended. The scheme is composed of the first-stage stilling basin with two high-low slope banks on the inlet and outlet respectively in the curved chute and the second-stage steep slope diffusion stilling basin, which has a baffle sill on the inlet and an anti-scour trench downstream the baffle wall to increase the rate of dissipation. The variation about the height of the buffer sills eliminates the transverse ultra-height in the curved section and affects the submerged degree of hydraulic jump in stilling basin. After optimization, the flow velocity in the inlet of apron is5m/s or so (flood frequency p=0.2%) and the rates of energy dissipation are above80%under different water levels.4. The composite energy dissipation system of multi-plunge with bottom-flow takes full advantage of the terrain, the dissipators are reasonably arranged and the mechanism of each dissipator is quite clear. The whole arrangement perfectly reflects the "stage-by-stage" and "section-by-section" energy dissipation optimization idea.