Study On Hydraulic Characteristics And The Optimization Of YJBY Hydropower Station Diversion Tunnel

The bank-side type diversion tunnel is generally arranged on the side of the mountain,affected by various factors such as the building’s own structural body type and the inlet terrain boundary,the inlet is prone to vortex,especially the through-suction vortex,which directly affects the safe operation of the diversion building.In addition,for high head,high flow rate and complex geological conditions in narrow river valleys,the problem of high speed water discharge and energy dissipation safety are more prominent,so it is also very important to choose a suitable outlet energy dissipation type.This paper relies on YJBY hydropower station hydraulic model test and three-dimensional hydraulic numerical simulation aided calculation method,the project right bank diversion hole inlet vortex hydraulic characteristics and export energy dissipation and other issues to carry out a comprehensive analysis and research,and form the recommended body type of diversion hole inlet and outlet,a better solution to the diversion hole project inlet vortex and outlet energy dissipation problem.The main research results are as follows:(1)The experimental observation of the original design body model of the upstream inlet of the inflow tunnel found that the incoming flow was asymmetrical leading to the emergence of vortices,and with the rise of the water level,the vortices gradually developed from the depression type to the through-suction type,and the duration of the suction vortices was long under the high water level working condition.(2)numerical simulation calculation results show that,changeing the inlet boundary conditions,excavateing the right side of the inlet open canal,the front surface of the inlet and water depth longitudinal flow symmetry,inhibit the surface ring volume generated,the circular flow field from the front of the inlet building offset to the right;change the inlet body type,the inlet backward sloping chest wall to flush vertical breast wall,reduce the inlet front of the stagnant area,the downward dragging force effect makes the water symmetrical from both sides into the hole This reduces the possibility of inducing vortices,and basically no circular flow field is generated in front of the inlet.Although both factors have an influence on the generation and development of vortices,the effect of changing the shape of the inlet to reduce the intensity of vortices is relatively more significant than changing the boundary conditions.(3)The test results of the model comparison between the vertical vortex elimination grille and the front inclined vortex elimination frame set in front of the inlet show that the diameter of the suction vortex is significantly reduced under the action of the front inclined vortex elimination frame,and the movement of the vortex is not enhanced with the increase of the upstream incoming flow,while the frequency of the formation of the through suction vortex is also significantly reduced.(4)In view of the problems of insufficient energy dissipation in the original design,narrow channel,left bank scoured by flood crest,mutual influence of water flow between the two tunnels outlets and serious scouring of the riverbed,the hydraulic parameters such as water flow,flow velocity and scouring characteristics of four layout options,including right bank guidance,cavern line offset,left bank diversion and forced energy dissipation +left bank diversion,have been measured and analyzed through physical model tests.(5)The results of the whole process test of the recommended body type of the diversion tunnel outlet show that: the composite energy dissipation body type has a high energy dissipation rate under all working conditions,the flow velocity at the cofferdam and near the left bank is obviously reduced,the dispersed water flow can effectively block backflow,the intensity of water surface fluctuation is weakened,the mainstream returns to the channel smoothly,the siltation situation is good,and the left bank is protected from scouring.The composite energy dissipation body type basically meets the project energy dissipation and safety and stability requirements,and also provides a reference and reference for similar diversion cavern engineering outlet design.