| A new energy dissipation method of "jet-swirl cascade energy dissipator" is proposed to solve the problem of diversion tunnel under super high water head being reconstructed into flood discharge tunnel.This energy dissipation method adopts the idea of hierarchical energy dissipation,one is jet energy dissipation,the other is horizontal swirl.It can decompose a super high water head into two middle and low water heads for flood discharge and energy dissipation,so as to solve the problems of energy dissipation and high-speed flow.Based on the National Natural Science Foundation of China's "Energy Dissipation Mechanism and Suitable Hydraulic Conditions of Jet-Swirl Cascade Energy Dissipator",the basic hydraulic characteristics of Jet-Swirl Cascade Energy Dissipator and the variation law between hydraulic parameters and water level under the condition of large water level change are analyzed and studied by means of model test and numerical simulation.The following conclusions are drawn:(1)The flow pattern of the energy dissipator in the jet-swirl cascade is closely related to the upstream and downstream water level.At different upstream and downstream water levels,the flow pattern in the jet section can be divided into free outflow and submerged outflow,and the flow pattern in the swirl section can be divided into free swirling flow,transitional flow and submerged swirling flow.(2)The velocity and pressure of the energy dissipator in the cascade have obvious sectional characteristics,and the pressure decreases and the velocity increases in the blocking section of the cascade.(3)The minimum number of cavitation in jet section is 0.64?1.27,and the minimum number of cavitation in swirl section is 0.57?0.94,which is larger than the initial number of cavitation in swirl tunnel.It shows that the cascade energy dissipator will not cause cavitation damage under different water levels.(4)The wall pressure of typical section of cascade energy dissipator increases linearly with the difference between upstream and downstream water level.(5)he overall energy dissipation rate of cascade energy dissipators is between 0.71 and 0.81,and the energy dissipation rate of jet section is between 0.25 and 0.38 in swirling section is between 0.43 and 0.47,which indicates that the energy dissipation distribution of cascade energy dissipator is reasonable.(6)The maximum turbulent kinetic energy in the jet section appears in the diffusion section,and the turbulent kinetic energy ratio in the swirl section appears in the cyclone and the diffusion section,which indicates that the main place for energy dissipation is after the diffusion section in the cascade energy dissipator. |
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