Study On The Variation Law Of Hydraulic Characteristics Of Water-gas Two-phase Flow In Rotating Diffusion Diversion Tunnel

Since the beginning of the 21st century,with the deepening of the western development strategy,the demand for energy in Northwest China has been increasing.Therefore,China will plan and build a number of high dams in the western region to solve the problem of energy shortage in the western region.As one of the main buildings of high dams,spillway tunnels play a great role in the flood discharge,construction diversion,water diversion and power generation of dams.However,since most of the high dams in the western region are built in high mountains and canyons,the discharge flow energy of spillway tunnels is large,which is easy to cause damage to the dams.Therefore,the energy dissipation of high dam spillway tunnels has been the focus of the research of water conservancy industry in China.The composite internal energy dissipation of swirl blockage and swirl diffusion is a new type of energy dissipation technology for high dam spillway tunnel,which not only solves the problem that the flow energy of high dam is not easy to consume,but also reduces the engineering quantity and saves the construction cost.However,due to the complex flow pattern of water-gas two-phase flow in the rotating diffusion diversion tunnel of the composite internal energy dissipation spillway tunnel adopting the composite internal energy dissipation technology of swirl blockage and swirl diffusion,and the technical means for measuring the high-speed swirling water-gas two-phase flow have certain limitations,there is little research on the hydraulic characteristics of water-gas two-phase flow in the rotating diffusion diversion tunnel of the composite internal energy dissipation spillway tunnel in China.Therefore,in this paper,combined with previous research results and methods of composite internal energy dissipation spillway tunnel,numerical simulation combined with model test research method is used to study the hydraulic characteristics of water-air two-phase flow in composite internal energy dissipation spillway tunnel with different upstream water levels（150m～200m）,different ventilation aperture and different exhaust modes under high head conditions.The main research results are as follows:（1）Under the condition of water levels（150m～200m）,the higher the upstream water level of the composite internal energy dissipation spillway tunnel is,the closer the position of the water-gas two-phase flow falling clear flow in the rotary diffusion diversion tunnel is to the tail of the tunnel,the greater the velocity of the water-gas stratification stage is,the higher the gas holdup is,and the greater the turbulent kinetic energy is.However,the larger the cavity negative pressure and wall pressure are,the more difficult the gas will escape.Therefore,the higher the upstream water level is,the better the energy dissipation effect of the rotary diffusion diversion tunnel is.（2）Under the conditions of different ventilation apertures,when the ventilation aperture of the composite internal energy dissipation spillway tunnel is D₀=0.2D,the gas cavity volume of the water-gas two-phase flow in the rotating diffusion diversion tunnel is the largest,and the gas is most likely to escape.When the ventilation aperture of the composite internal energy dissipation spillway tunnel is D₀=0.3D,the wall pressure,gas content,turbulent kinetic energy and dissipation rate are the largest,and the energy dissipation effect is better.（3）Compared with the rotating diffusion diversion tunnel without vents,the water-gas two-phase flow in the rotating diffusion diversion tunnel with vents is more likely to form a falling open flow,the flow rate is lower,the gas is easier to escape,and the turbulent kinetic energy is higher.However,a large range of negative pressure will appear on the wall of the tunnel,which is easy to cause cavitation and cavitation on the wall of the rotating diffusion diversion tunnel.Therefore,the rotating diffusion diversion tunnel without vents can better ensure the safe operation of the composite internal energy dissipation spillway tunnel.