Abstract
This study analyzed the normal use of an unusual flood-releasing tunnel with a plug dissipator. Firstly, normal physical model tests based on the Froude criterion (1 : 50) were finished. Secondly, depression physical model tests based on the Froude criterion (1 : 50) and cavitation similarity criterion were finished. Thirdly, 3-dimensional numerical simulation of flow field was finished, and free surface profile was captured, which was based on RNGk-εtwo-equation turbulence model and VOF method. The focus of this study is on the relationship between normal use and cavitation characteristics (e.g., pressure, turbulence kinetic energy, and cavitation number). The results show that lowering the reservoir water level, reduced by 20.41 m at most, increases the risk of cavitation of a plug discharge tunnel, which means with the decrease of the flow cavitation number, the possibility of structural damage will increase dramatically, while reducing the outlet height can effectively raise the flow cavitation number, ensuring the safety of normal use. Under the conditions of free outflow, for theH1/evalues of 4.45, 4.00, and 3.55, the conditions in which the tunnel meets the requirements of anticavitation areh/D ≤ 0.42,h/D ≤ 0.39, andh/D ≤ 0.35, respectively. In addition, the discharge capacity of the tunnel is not significantly reduced with the lowering of outlet height, implying that operation under a low water head of the plug discharge tunnel, as low as 3.55 ofH1/ein the test, is feasible. The results obtained in this study can serve as reference information in engineering design of the plug discharge tunnel.
Highlights
Rebuilding the diversion tunnel into the discharge tunnel is a cost-effective approach that can reasonably utilize waste resources and increase the operational flexibility of engineering operations. e plug is a new internal energy dissipator that realizes the goal of drastic energy dissipation through the sudden enlargement and contraction of the water-crossing section [1]
Li et al [6] studied the way of adding vent holes in the recovering area of the plug to increase the possibility of anticavitation damage of the plug flood tunnel and obtained positive results. e results show that, by setting vent holes in the recovering area, air can be diffused to the two side walls, thereby effectively protecting the plug discharge tunnel. ese studies mainly focused on the influence of different plug geometries on the flow characteristics, such as wall pressure characteristics and aeration protection length
The normal use of the plug discharge tunnel is realized by changing the outlet height. e key hydraulic parameters are compared using model tests and numerical simulations. e results show the following: (i) e RNG k-ε two equation turbulence model can be used to perform numerical simulation of the complex plug discharge tunnel and obtain satisfactory results
Summary
Rebuilding the diversion tunnel into the discharge tunnel is a cost-effective approach that can reasonably utilize waste resources and increase the operational flexibility of engineering operations. e plug is a new internal energy dissipator that realizes the goal of drastic energy dissipation through the sudden enlargement and contraction of the water-crossing section [1]. E Xiluodu Project located in the Jinsha River studied the flood plugging tunnel of the pressurized shaft, and it was found that its energy dissipation rate and anticavitation performance still meet the requirements under a flow rate as high as 2700 m3/s, indicating that the use of a plug energy dissipator for releasing larger discharge is feasible [10]. In view of the fact that the plug is still a new type of energy dissipator, it is often designed as an unusual flood discharge tunnel in engineering, which means it is only used in operation under extreme conditions. The decrease in the outlet height will affect the discharge capacity and energy dissipation rate of the tunnel. E main focus of the present study is to investigate the features of discharge capacity, pressure, energy dissipation rate, and cavitation number of a plug discharge tunnel. E “curve pressure slope outlet” body shape is made up of a circular curve, which requires the horizontal distance limited to be 26.1 m, and the tangent line of curve end needs to be horizontal. e variation in the height h of the pressure outlet is 4.0∼7.5 m, and the top plate is connected by a single arc curve. e horizontal length of the curve is kept unchanged at 26.1 m, and the radius ensures that the angle between the endpoint tangent and the horizontal direction is zero
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
