Study On Hydraulic Characteristics And Stability And Safety Of Ski-drop Flow In Plunge Pool Of High Arch Dam

High arch dam project generally has the characteristics of"high water head,large discharge,narrow valley,concentric concentration of water flow"and so on.The arrangement of flood discharge and energy dissipation is very important and complex,and ski-drop water cushion pond is a kind of common and economical arrangement of flood discharge and energy dissipation for dam body.Its hydraulic characteristics and safety and stability still need to be deeply studied.On the basis of sorting out and analyzing the previous research results,this paper takes the water cushion pond of a high arch dam project as the research object,combined with one of the national key research and development program contents(Real-time Control Technology of Flood discharge Operation Safety in Hub 2016YFC0401904),using hydraulic integral Model Test and numerical Simulation Research method,the hydraulic characteristic response and safety stability of the dam body flood discharge and energy dissipation are studied by adjusting the structural type of the drainage structure and the change of water flow conditions.The main research contents and achievements are as follows:(1)The hydraulic characteristics of water cushion ponds with different middle hole angle combination conditions(-5°,0°,5°,10°)are studied.The correlation between the angle?,the collision superposition ratio?,the water entry area A and the impact pressure?P_m of the bottom plate is determined:With the increase of the angle of the middle hole,the position of the collision point between the surface hole water tongue and the middle hole water tongue shifts upstream,and the height of the water tongue collision point rises.Proper increase of middle hole angle can increase the angle of water tongue collision intersection?,ensure a certain energy dissipation rate of air collision,and reduce collision superposition ratio?,which can disperse water flow,expand water entry area A and reduce impact pressure?P_m of bottom plate of water cushion pond.(2)The response relationship of hydraulic characteristics of water cushion ponds with different surface hole shapes(equal width type for side surface hole,diffusion ridge,wide tail pier,tongue ridge,swallow tail ridge,etc.in middle surface hole)for collision energy dissipation is studied.The influence of structural type change on bottom plate impact pressure?P_m bottom,side wall impact pressure?P_m side and second way dam impact pressure?P_m dam is analyzed.The overall safety and stability of the cushion pond should weigh the hydraulic characteristics of the bottom plate,the side wall and the second dam at the same time.The swallow tail drop-20°scheme is relatively effective.(3)A relatively optimal scheme based on the equal width of the edge hole outlet and the swallow tail with the middle surface hole-20°and the angle of the middle hole(0°-10°-10°-0°).The safety and stability control indexes of water cushion pond(energy dissipation rate per unit water body,root mean square root of fluctuating pressure,maximum impact pressure,pressure gradient,etc.)are preliminarily analyzed.At the same time,the effects of the change of flow conditions on the dynamic water pressure impact zone and pressure gradient of the floor are compared and the basic laws are analyzed.