| Adding the blocking-gradual expansion facilities in the horizontal swirl spillway tunnel can obviously increase the pressure and decelerate the speed of the horizontal swirl tunnel section,eliminate the negative pressure at the outlet of the swirl generator under high water head,improve the cavitation conditions in the tunnel,and significantly increase the energy dissipation rate in the tunnel.Due to the complexity of the swirling motion in the cavity,this paper studies the swirling flow in the cavity of the swirling blocking spillway tunnel by using the model test,the RNGAk-? two-equation turbulence model and the VOF two-phase flow model,combined with the hydraulic characteristics of the energy dissipator shearing two-phase flow in the combination of swirling blocking and swirling diffusion,which is supported by the National Natural Science Foundation of China.The main results are as follows:(1)The numerical simulation method of blocked cavity swirl is analyzed and discussed,and the simulation method suitable for rotating water-gas two-phase flow is selected.The numerical simulation results are in good agreement with the experimental results,which verifies the feasibility of the method.(2)The diameter and swirl angle of the cavity decrease gradually along the horizontal tunnel section and increase gradually after the beginning of the blocking section;the diameter of the cavity decreases with the increase of the upstream water level.(3)The pressure in the bottom area near the end of the screwdriver is slightly larger,and the concentric circle distribution at the bottom of the cross section is slightly larger.The pressure of horizontal section fluctuates slightly along the course,and the pressure of section distributes in a concentric circle with a slightly larger bottom.The pressure of the blocking section decreases along the course,and the pressure of the section also has a similar concentric circle distribution law.With the increase of upstream water level,the wall pressure of shaft tunnel increases,and the pressure from screwdriver to blocking section increases approximately linearly.The pressure of blocking diffusion section changes little with the upstream water level when it flows freely downstream,and increases with the upstream water level when it floods out.(4)The average velocity of cross-section decreases gradually from the opening of the screwdriver to the direction of flow,and increases sharply after the blocking section.The tangential velocity shows the characteristics of free vortices in the horizontal tunnel section from z/D=0 to z/D=2,and the combined vortices of free vortices and forced vortices after z/D=2.Axial velocity decreases along the course,and the distribution of velocity near the wall is smaller than that near the atmospheric water interface along the radial direction from the horizontal tunnel section to the blocking section,and more uniform along the radial direction in the blocking section.(5)The high turbulence region occurs at the end of the cyclone and the diffusion zone.The turbulence of the water layer near the interface of the intake cavity is larger on the cross section.The turbulence energy of the diffusion zone in the downstream submerged outflow condition is larger than that in the free outflow condition.(6)The energy dissipation rate of the swirl er and the horizontal swirl section can reach more than 40%,and the total energy dissipation rate can reach about 90%when the water-air mixing energy dissipation in the diffusion section and the energy dissipation in the retreat tunnel are added. |
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