The Study Of The Gate Slots Cavitation Characteristics And Numerical Simulation

With the development of the hydraulic engineering, a lot of huge hydroelectric stations and high dams have been constructed, which means the maximum velocity of the flood discharge will come to 50.0m/s approximately. With the increase of the operating head and the velocity, the cavitation of gate slots will be more frequent. However, the experimental and theoretical study on diminishing cavitation damages has focused on the problems of low velocities so far. The mechanics of the gate slots cavitation and its relative factors have still been unknown. To provide scientific bases for the design and operation, the characteristics of the gate slots cavitation should be studied further.Based on former researches, the types of the gate slots cavitation and its relative factors were analyzed and the cavitation characteristics of different gate slots were compared and summarized. At a velocity of 30m/s, the cavitation of rectangular gate slots with different breadth depth ratios and different bullnose ratios was simulated. Numerical models were also applied in practical projects. In addition, to study inner regularities of the cavitation generation and scale effects of the experiment, model investigations of sudden enlargement flow with high velocities (30-40m/s) were performed at different sudden enlargement ratios.The main contents and results are as follow, (1) Cavitation damages are mainly caused by the vortex cavitation but notseparation cavitation. The primary factors influencing the gate slots cavitation are the parameters of breadth depth ratios (WID) , staggered range ratios ( A/ W ) , slope ratios ( A/X ) , and bullnose ratios CR/D) .(2) At a high velocity, the standard k ~ s model was adopted to simulate the flow of a rectangular gate slot of a pressure and long tunnel to further study the characteristics of the flow field, pressure, and cavitation. The variable density model was also used. The flow and pressure fields of the cavitation of gate slots were analyzed qualitatively. At a velocity of 30m/s, the most suitable breadth depth ratios of rectangular gate slots are between 1.2 and 1.9 and the optimal ones are between 1.3 and 1.7.(3) The flow of the shaft gate slot of the Xiluodu diversion tunnel was simulated, and computational results agreed well with measured data. It is shown that the numerical method and simulate results are right and reliable. Computational results indicates the design of the gate slot( W/D=l.33)is feasible and the cavitation does not occur at the highest velocity.(4) Cavitation experiments of high speed and sudden enlargement flow with different ratios were performed. At a high velocity, the modified formula of the velocity scale of incipient cavitation numbers was obtained by analyzing the relation between the incipient cavitation number and velocity.