Study On The Downstream Scour Of Spillway And Hydraulic Characteristics Of The Plunge Pool In Kong Lang Reservoir Project

Rivers and lakes contain extremely rich water and water resources.The development and utilization of these natural water resources can bring huge economic benefits.Building a reservoir project is one of the most common methods to develop and utilize these resources.Statistics on the current methods of the hydroelectric power engineering show that the most used form is ski-jump type.However,the scouring problem of the downstream riverbed brought by the ski-jump type is directly related to the safety and stability of the dam,and it has always been the focus of constant exploration in the field of hydraulics.Kong Lang reservoir project has the characteristics of high water head,large single wide flow and special topography of downstream river,and It can be used as an engineering example to study the local scour problem caused by the efficiency of high dam.Taking Kong Lang reservoir project as the research object in this paper,hydraulic model test,and three-dimensional numerical simulation are combined to provide a reference research method for the high dam ski-jump type flood discharge and energy dissipation.At the same time,the theoretical analysis method is used to obtain the estimation formula for predicting the scour depth expecting to forecast the high dam scour depth more accurately.The main results are as follows:(1)Based on the extremely complex topographic conditions of Kong Lang reservoir project and the special situation of nearly 100 meters water level difference,the physical model test is conducted to obtain the design of spillway which meets the requirements of spillway energy dissipation.The physical test results of the downstream scour guide the form of the flip bucket,and the optimized type of the flip bucket is obtained,the jet nappe direction is effectively improved to avoid the deflected stream,the slope instability caused by the position of the scour deflecting to the left bank of the river is corrected,letting the deepest scour point is located in the main channel,which effectively reduces the scour range and makes the scour shape more regular,and overcomes the bad flow pattern caused by the special topography.(2)Using the method of RNG k-? two-equation turbulence model combined with the VOF method to capture the free water surface,the three-dimensional numerical of the whole process of water-gas two-phase flow from the reservoir to the spillway to the downstream plunge pool of the Kong Lang Reservoir spillway project is obtained.The physical quantities related to the upstream spillway are verified,and the simulation results are in good agreement with the test results,indicating that it can be used for the next step of numerical simulation experimental study,to simulate the flow field in the downstream plunge pool,and to analyze the hydraulic characteristics of the water flow in the downstream plunge pool.(3)The velocity field,the water-air ratio,the pressure field,the turbulent kinetic energy and the dissipation rate distribution of the turbulent kinetic energy were obtained by numerical simulation,and the three-dimension flowing was analyzed,so as to study the further development of the scour hole.According to the distribution characteristics of the pressure field in the plunge pool and the pressure peak of the impact point,it indicates that the greater impact pressure of the water flow on the riverbed,the more severe the scouring will be.By analyzing the distribution of the turbulent kinetic energy and the turbulent kinetic energy dissipation rate,it can be seen that the values of both of them reach the maximum value near the impact point,indicating that these regions are the main areas of water flow energy transfer and dissipation.(4)The main influencing factors of local scour downstream of high dam overflows are analyzed,including single width flow rate,head difference and sediment particle size.Based on the experimental results of Kong Lang reservoir project and a large number of prototype observation data,the empirical formula for estimating the scour depth is obtained.In order to verify the applicability of the formula,the formula is verified by the measured scour data of the other three hydropower stations.The results show that the calculated values are in good agreement with the measured values,which can provide a basis for the scour depth estimation of other similar high dams.