Study On The Hydraulic Characteristics,Discharge And Energy Characteristics Of Jet Swirl Cascade Energy Dissipator

Jet swirl cascade internal energy dissipation is a new type of energy dissipation under super high water head,which has a wide application prospect.It can transform a high head problem into two or more low and medium head problems,so as to solve all kinds of high-speed flow problems existing in single internal energy dissipator in high head flood discharge and energy dissipation,and make it possible to reconstruct the diversion tunnel of high dam to save project investment.The energy dissipation mode consists of two stages:the first stage of submerged jet energy dissipation and the second stage of swirling energy dissipationBased on the National Natural Science Foundation of China "energy dissipation mechanism and suitable hydraulic conditions of jet swirl cascade internal energy dissipator",this paper uses the methods of model test,numerical simulation and theoretical analysis to study the hydraulic characteristics,discharge law,energy change of each part and energy dissipation rate of jet swirl cascade,and evaluates the possibility of cavitation.The main research results are as follows:(1)Flow pattern division of cascade energy dissipator:the jet section is not submerged jet,and the swirl section is not stable cavity rotating flow;the jet section is not submerged jet,and the horizontal swirl section initially forms a relatively stable cavity rotating flow;the jet section is submerged jet,and the swirl section forms a stable cavity rotating flow.When the upstream water level is H≥ 8.8D and the water level of vertical shaft submerged the top of jet energy dissipation section,the cascade energy dissipater can meet the bistable operation conditions.(2)The pressure in the contraction section of the jet decreases suddenly,but remains unchanged in the tailrace section of the jet;the wall pressure in the swirl section decreases obviously in the swirl blocking section,and the change of the upstream water level has a great influence on the wall pressure in the swirl section(3)The velocity increases rapidly in the jet contraction section and the swirling flow blocking orifice section.The tangential velocity value of the cross section along the swirl section starts from the edge of the cavity and increases first and then decreases along the radial direction.(4)The discharge coefficient of the orifice in the jet contraction section is related to the parameters of the velocity head coefficient and the pressure of the contraction orifice,the discharge coefficient of the spinner throat is related to the head loss along the way,the pressure of the spinner throat,etc.,the discharge coefficient of the blocking orifice is related to the head loss along the way,the swirl angle,the cavity radius,the pressure strength characteristics,etc..(5)The main energy dissipation section of cascade energy dissipator includes jet contraction section,swirling energy dissipator section and blocking diffusion section.The total energy dissipation rate is about 81%.(6)There is cavitation possibility in the front section of jet back water tunnel when the upstream water level is 8.8D;there is cavitation possibility in the front section of swirl back water tunnel when the downstream is submerged.However,the air entrainment in the diffusion section is sufficient and uniform,and the probability of cavitation damage is reduced,and other air defense measures are proposed.