An improper design of an air vent will not only cause waste of resources but also seriously threaten the safety of the spillway tunnel. The present study analyzes the effects of the area and position of the air vent on the air supply, using the volume of fluid method with the k–ε turbulence model. The air speed in the air vent will decrease with an increase in the area, but the quantity of air supplied will increase. When the area of air vents is equal to the tunnel residual, the air supply capacity of the air vent reaches the maximum. A relationship between the quantity of air supplied and the area of the air vent is put forward, and the error with the prototype observation result is about 10%. The distribution of negative pressure in the tunnel may be improved by arranging the air vent in a proper position; the quantity of air supplied also decreases as the distance between the air vent and the pressurized conduit increases. In general, it is more advantageous to position the air vent upstream. These results provide a reference for the air ventilation design in hydraulic engineering.
Due to the high flow velocity and easy cavitation of high-head drainage tunnels, it is usually necessary to set up aeration facilities. In particular, when the bottom slope of the tunnel is mild, the aeration facilities often have problems such as difficulty with air intake, short cavity, and serious water accumulation, which aggravate the risk of cavitation damage. In this paper, based on the Rumei hydropower station and the Gushui hydropower station, a method combining theoretical analysis and model testing is used to solve the connection problem between the aeration facility and the 3% mild bottom slope of a tunnel body, and the aeration facility shape of “lifting ridge + flat (mild) slope + steep slope” is put forward. The research shows that the steep slope section can smoothly connect the water flow over the cantilever, reduce the jet impact angle, prevent the water from backtracking, and produce a long and stable cavity in the flat (mild) slope section. The aeration concentration along the bottom of the tunnel is higher than 3% at 140 m over the top of the dam. The aeration effect of this type is better, and it can provide effective long-distance protection for a drainage tunnel with high head and a mild bottom slope.
Maximum pressure is one of the key factors that affect jet scouring. Previous studies have focused on the attenuation characteristics of the submerged jet, but there are few studies on the influence of the nappe shape on the pressure of the plunge pool. In this paper, a combination of numerical simulation and physical experiments was used to determine the influence on the maximum pressure of the vertical rectangular submerged jet with different aspect ratios (1, 3, 5, 8, 11.25, 15, and 20), incident flow velocity, and water depth on the plunge pool bottom. The hydraulic diameter, D, of the entering interface was proposed to measure the degree of dispersion of the nappe, based on which an empirical formula for the maximum pressure on the plunge pool bottom was obtained. By applying the formula to other shapes of jets (rhombuses, triangles, circles, ellipses, etc.), higher precision calculation results were also obtained, and the formula calculation results were in good agreement with the test results of the existing literature.
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